Acc. No. Dc 6 - Dspace @ Jadavpur University

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STUDY ON THE SYSTEM TESTING PROCEDURE FOR EVACUATED TUBE SOLAR WATER HEATING SYSTEM A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE AWARD OF THE DEGREE OF MASTER OF TECHNOLOGY IN ENERGY SCIENCE AND TECHNOLOGY 2010 SUBMITED BY TARAK NATH CHELL UNDER THE SUPERVISION OF DR. SUBHASIS NEOGI READER SCHOOL OF ENERGY STUDIES JADAVPUR UNIVERSITY FACULTY OF ENGINEERING AND TECHNOLOGY JADAVPUR UNIVERSITY KOKATA-700032 1 FACULTY OF ENGINEERING AND TECHNOLOGY JADAVPUR UNIVERSITY KOLKATA-700032 RECOMMENDATION CERTIFICATE Certified that the work entitled “STUDY ON THE SYSTEM TESTING PROCEDURE FOR EVACUATED TUBE SOLAR WATER HEATING SYSTEM’’ has been completed by Mr. Tarak Nath Chell under our supervision. This work may be accepted in the partial fulfillment of the requirements for the degree of Master of Technology in Energy Science and Technology. To the best of our knowledge, this work has not been submitted for the award of any degree or diploma. ──────────── ───────────── Dr. Subhasis Neogi Teacher In-charge Supervisor and Reader (M-Tech program) School of Energy Studies School of Energy Studies Jadavpur University Jadavpur University ─────────────── Prof. Niladri Chakraborty Dean Faculty of Engineering & Technology Jadavpur University 2 FACULTY OF ENGINEERING AND TECHNOLOGY JADAVPUR UNIVERSITY KOLKATA-700032 CERTIFICATE OF APPROVAL The foregoing thesis is hereby approved as a creditable study of a technological subject carried out and presented in a manner satisfactory to warrant its acceptance as a pre-requisite to the degree for which it has been submitted. It is understood that by this approval the undersigned persons does not necessarily endorse or approve any statement made, opinion expressed or conclusion drawn therein but approve the thesis only for the purpose for which it has been submitted. Committee of __________________ Final Examination for Evaluation of Thesis ____________________ 3 ACKNOWLEDGEMENTS I feel honoured to express my deepest respect , reverence, indebtedness and heartiest gratitude to my respected guide Dr. Subhasis Neogi (Reader, School of Energy Studies) for his acute interest in each and every minor details of this project, judicious guidance, constant inspiration, and help during the entire period of execution of present project work and also making the theme of the project work. I am also grateful to Prof. Biswajit Ghosh (Director, School of Energy Studies, Jadavpur University), Dr. Tushar Jash (Senior Lecturer, School of energy Studies) and Mr. Ratan Mandal (Senior Lecturer, School of Energy Studies) for their valuable kind advice and encouragement during the period of work. I convey my special thanks to Prof. Avijit Kar (Computer Science and Engineering, Jadavpur University) for extending his co-operation and support wherever necessary during the course of my project. I am thankful to Dilip Das and Ujjal Nath (Departmental staff) and few of my fellow pupil for their constant motivation assistance during the project. Perhaps for the first time I get a formal occasion to thank my family who supported me every moment of my life without charging anything in return. School of Energy Studies, Tarak Nath Chell Jadavpur University, Kolkata-700032 . 4 DEDICATED TO MY FAMILY AND MY TEACHERS 5 Contents Nomenclature Page No 08 Chapter 1: General introduction 1.1 General introduction 11 1.2 Review of earlier work 13 1.3 Object & scope of work 25 Chapter 2: Solar radiation and geometry 2.1 Introduction 27 2.2 Solar geometry 27 2.3 Solar radiation on a surface 31 Chapter 3: Evacuated tube collector 3.1 Introduction 35 3.2 Working principle 35 3.3 Types of collectors 36 3.4 Basic working principle of heat Pipe ETC 38 3.5 Technology of eliminating different problems 39 3.6 Advantages & disadvantage 42 3.7 Evacuated tube versus flat plate technology 43 Chapter 4: Experimental procedure and setup 4.1 Introduction 45 4.2 Day-time performance 45 4.3 Night-time performance 46 4.4 Test conditions 47 4.5 Experimental determination 47 4.6 Measurements of physical specifications 49 4.7 Pre-conditioning test 50 4.8 Static pressure leakage test 50 4.9 Day time test 51 6 4.10 Night time test 52 4.11 Instrument used in the experimental setup 53 4.12 Developed testing facility for two collector simultaneously 71 4.13 Develop coding flow chart 72 Chapter 5: Results and discussions 5.1 Calculation of solar noon 74 5.2 Calculation of mass capacitance 74 5.3 Gross area of collector 75 5.4 Day time test 75 5.5 Night time test 75 5.6 Day time test curve 76 5.7 Day time heat loss calculation 77 5.8 Pressure test 77 5.9 System efficiency at standard test conditions 77 5.10 Thermal energy stored in the storage tank of the day time test 78 5.11 Impact of time constant on performance efficiency 88 5.12 Recommendation of tank volume measurement 89 Chapter 6: Conclusion and scope of future work 6.1 Conclusion 91 6.2 Scope of future work 91 References: 91 7 Nomenclature Ac Gross area of solar collector, m2 Aa Absorber area of solar collector, m2 Ap Total outside surface area of the connecting pipes, m2 Ap’ Total outside surface area of pipes which may be for loosing heat during night-test, m2 As Outside surface area of storage tank, m2 Cp Specific heat of water, J/kg K F’ Collector efficiency factor GT Solar irradiance on the inclined plane of the solar collector, W/m2 GT Average value of solar irradiance on the inclined plane of the solar collector during day-test, W/m2 (MC)s Thermal capacitance of the water in the storage tank only (J/K). Q Total energy collected by the solar collector during period of the daytest (kWh) Qc The total solar irradiance on the collector during test period, (MJ/m2) t Time , s Ta Ambient air temperature, ºC Tad Average ambient air temperature during day-test, ºC Tan Average ambient air temperature during night-test, ºC Tm Cold water temperature from mains, ºC Ts Temperature of water in storage tank Tsfn Storage temperature at the end of night-test, ºC Tsfd Storage temperature at the end of the day-test, ºC Tsid Storage temperature at the start of the day-test, ºC Tsin Storage temperature at the start of the night-test, ºC USys, d Overall heat loss coefficient of the system during day-test, W/m2 K UL Overall heat loss coefficient of solar collector, W/m2 K Usn Overall heat loss coefficient of system during night-test, W/m2 K Up Overall heat loss coefficient of piping, W/m2 K Us Overall heat loss coefficient of storage tank, W/m2 K 8 Greek Symbols ∆t Time duration of solar test, s ηsys,o Maximum efficiency of the system hsys Efficiency of solar hot water system averaged over the test period (τα)eff Effective transmittance –absorptance product of the solar collector for solar radiation τcooling Cooling time constant during no radiation period, day Subscripts a Ambient Conditions c Collector d Day time f Final value i Initial Value n Night time p Pipe s Storage Tank T On tilted collector surface 9 Chapter 1 General Introduction 10 1.1 Introduction The radiation continuously showered on earth by the sun represents the most basic and inexhaustible source of energy which is the mother of all forms of energy conventional or non-conventional, renewable or non-renewable the only exception being nuclear energy. The sun emits radiant energy as a spectrum corresponding to a black body at a temperature of 5500 °C, of which only a small amount is intercepted by the earth. Solar radiation is absorbed in the atmosphere and at the earth surface at a rate of 10.3 ×1016 W which is low compared with that of global energy consumption (9×1012W). The heat from sun causes continuous evaporation of water from the oceans, lakes, rivers, plants and soil. The solar radiation also heats up the atmospheric air. Due to the variation of terrain condition and geographical location the localised heating effect causing various variation in different ambient condition. Sun is the ultimate source of all energy. It is basically giant fusion reactor, converting hydrogen into helium and radiating energy of 3.85×1026 watts into space. The amount of energy intercepted by the earth’s atmosphere is 1.73×1017 watts, a tiny fraction but equivalent to burning 6.5 million tones of coal each second. The amount of energy actually reaching the earth’s surface per unit time per unit area perpendicular to the sun’s rays is called the solar constant with a value of 1.341 Kw per sq. m. A more convenient figure to remember is 2 calories per sq. cm per minute. This value varies very little. Nearly ninety nine per cent of the total solar radiation is contained in the wavelength region between 0.276 and 4.96 microns (micro meter). This radiation travels with a speed close to 3, 00,000 Km per second and reaches the outer atmosphere of the earth located at an average distances of 1.5 ×108 Km from the sun. Above 80 Km oxygen absorbs radiation having wavelength shorter than 0.2 micron. At elevation between 20 and 50 Km, ozone selectively absorbs the solar radiation with wavelengths between 0.2 and 0.3 micron. 11 Consequently, by the time the solar radiation reaches the earth’s surface practically all of it with wavelength below 0.3 micron and above 0.7 micron is absorbed by gases in the upper atmosphere. From the point of the solar energy utilization the 0.3-0.7 micron region of maximum intensity covering near ultraviolet –visible region is of importance. The art of extracting power from the solar energy source is based around the principle of capturing the short wave solar radiation and preventing it from being reradiated directly to the atmosphere. Glass and other selective surfaces are used to achieve this. Glass has the ability to allow the passage of short wave radiation whilst preventing heat from being radiated in form of long wave radiation. For storage of this trapped heat, a liquid or solid with a high thermal mass is employed. In a water heating system this will be the fluid that runs through the collector. If solar energy is being used to heat water by means of a collector panel, is critical to the level of solar gain and hence the increase in temperature of the water. Most solar water-heating collectors are fixed permanently and therefore cannot be adjusted. There are many applications for the direct use of solar thermal energy, space heating and cooling, water heating, crop drying and solar cooking. It is a technology which is well understood and widely used in many countries throughout the world, especially in areas with high solar insulation (the total energy per unit area received from the sun). As world oil prices vary, it is a technology which is rapidly gaining acceptance as an energy saving measure in both domestic and commercial water heating applications. Water heating technologies are usually referred to as active solar technologies, whereas other technologies such as space heating or cooling which passively absorb the energy of the sun and have no moving components, are referred to as passive solar technologies. More sophisticated solar technologies exist for providing power for electricity generation. 12 1.2 Review of Earlier Work In this paper the author Y.C. Soo Too et al. (2009) develop a model of narrow gap vertical mantle heat exchangers that has been implemented in the TRNSYS solar simulation package to evaluate annual thermal performance of solar domestic water heaters incorporating narrow mantle heat exchangers with a two-pass arrangement. The long term performance of a pumped circulation solar water heater with a 3 mm gap vertical mantle heat exchanger in Melbourene (latitude of -38º) and Sydney (latitude of -34º) was shown that monthly energy savings during summer months are approximately 90% in both location but winter, monthly energy saving in Sydney and Melbourene are 52% and 29% respectively. The performance simulation was shown that the annual energy saving for a direct-coupled system is approximately 10% higher a mantle system in both Sydney and Melbourene. It is found that the loss of performance may be acceptable given the advantage of freeze protection that the mantle heat exchanger provides. In this paper the author K.K. Chong and C.W. Wong (2009) derived a general formula for on axis sun tracking system that consists of two orthogonal driving axes with any arbitrary orientation to tackle the problem of installation defect. Here azimuth elevation and tilt-roll tracking formulas are specific cases. The application of the general formula is to improve the sun tracking accuracy because the misalignment of solar collector from an ideal azimuth elevation or tilt roll tracking during the installation can be corrected by a straightforward application of the general formula. They studied 0.4º installation error of azimuth elevation sun tracker has given a signification effect to the performance of high concentration solar modules. In this paper the author Johan Vestlund et al. (2009) detail studied thermal performance of flat plate collectors with different gas fillings between absorber and cover glass. They used Matlab based mathematical model for their experiment and all calculations done by numerical methods. They were concluded the gas filling technique of solar collector to achieve thinner collector design with the better performance than the standard collector. The thin Argon, Krypton, Xenon filled 13 collector also showed better performance from the CO2 or air filled collector. Then the thin construction means that the required amount of gas is despite the gas price. In this paper the author K. Sopian et al. (2009) conducted experimental studies on the double pass solar collector with or without porous media in the second and a theoretical model consists of a solar collector and a solar simulator. They were all experimental and theoretical result commenced and compared and concluded the addition of the porous media in the second channel of the double pass solar collector increases the performance of the collector. Porous media in the second channel increases the heat transfer area. This type of collector has a higher thermal performance compared to the conventional single pass solar collector. The thermal efficiency of the double pass solar collector with porous media is about 60 -70%. In this paper the author Milton Matos Rolim et al. (2009) developed an analytic model of a solar power station and compare SEGS VI-30MWe power plant. The model combines two subsystems, solar collectors field and the power station. They observed simulation based parabolic through LS2 collectors with evacuated absorbers efficiencies vary 0.73 to 0.63 and non evacuated absorbers efficiencies vary 0.70 to 0.58.They described from analytic model when evaporation temperature 320ºC using evacuated absorber then overall efficiency 0.262 and evaporation temperature 310ºC, with non evacuated absorber then overall efficiency 0.234 and evaporation temperature 300ºC, with bare absorber (without glass) then overall efficiency 0.219.The temperature obtained for evacuated absorbers is very close to the values observed in SEGS VI-30MWe power plant. So the analytic model developed, shows the good precision of electric solar plants with parabolic through collectors. In this paper the author N. BENZ et al. (1996) investigated the reduction of gas heat conduction in evacuated flat plate collector with operating pressure between 103 and 104 Pa. They were heat loss experiments conducted a real size model pressure dependency of the thermal losses was examined for air, krypton and a nanostructure SiO2 aerogel power insulation between absorber and real side of the casing. The experimental result showed Krypton gas filling EFPC reduced gaseous 14 conduction 65% in the continuum range with respect to air. In low emissive EFPC where gas conduction losses are comparable to radiative losses, the reduction in total loss is about 30% and unpacked aerogel the heat conduction could be reduced 50% in operation pressure 103 Pa. In this paper the author Soteris Kalogirou (2009) was presented most widely renewable energy used system the thermosiphon solar water heating system. He concluded that the environmental impact of any energy system is an important factor and solar systems have the potential to reduce environmental pollution. For the domestic solar heating system compared to a conventional system electricity or diesel backup and the result showed that the saving is about 70%. The annual solar contribution is 79% whereas the payback time of the system is 2.7 year and the life cycle savings are 2240 € for electricity backup and 4.5 years and 1056 € for diesel backup with respect to life cycle assessment of the systems, the energy spent for the manufacture and installation of the solar systems is recouped in about 13 months, whereas the payback time with respect to emissions produced from the embodied energy required for the manufacture and installation of the systems varies from a few months to 3.2 years according to the fuel and the particular pollutant considered. In this paper the author I. Budihardjo et al. (2009) developed of a simulation model in TRNSYS simulation program to evaluate the performance of solar water. They were studied characterise of the system components i.e. collector optical efficiency, collector heat loss, storage tank heat loss and natural circulation flow rate through the single-ended water-in-glass collector tubes. After that they were compared system performance of a selective flat plate system and two configurations of water-in-glass systems with 30 tube 2.9 m2 collector array at 22° inclination and 220-L tank operating in Sydney are compared The flat plate system has an annual energy savings of 77% the single tank evacuated tube system has an annual saving of 70.9% and evacuated tube solar pre-heater with a boost tank has a savings of 66.2%. Another result showed that an evacuated tube system with 30 tubes has slightly lower energy savings than a two panel (3.7 m2) flat plate system. The 15 performance of evacuated tube collector system was less sensitive to tank size than flat plate collector systems In this paper the author Naum Fraidenraich et al. (1997) mathematically analyzed how improved thermal power and temperature delivered in liner solar collectors. They mentioned that three procedures were adopted. First was the collector heatloss coefficient as constant along the absorber and used the well-established close from solution. This procedure main problem was higher temperature needed for steam generation. Another was heat loss rate is significant relative to optical gains. Second was an analytic model of, the main drawback that temperature dependence of collector heat loss was expressed in term of fluid rather than absorber temperature. The system was many problem physically implementation. Third was solved problem governing heat balance differential equations numerically. So they had been adopted concentrator parameters commercially developed parabolic through concentrator for intermediate pressure steam production. Consider a liner focus collector of geometric concentration with an evacuated selectively coated tubular receiver of absorber circumference. The analytic solution was applied that short initial length for its own lower value. The outlet temperature from that segment then served as inlet for the absorber section with concentrated flux. They were concluded solution can be done numerical solution of the governing equations the analytic approach offer a clearer view of basic function of implemented. In this paper the author T. N. Anderson et al. (2008) developed a special type one dimensional steady state thermal model building integrated photovoltaic / thermal (BIPVT) solar collector for analyze the thermal and electrical performance. He mentioned photovoltaic and solar thermal can be used together in domestic purpose for maximum utilization of solar energy. He observed PV cells tend to converted short wavelength radiation to electricity while longer wavelengths in heating of the laminate. Heat is transfer cells through the laminate to the fluid and on the other hand fluid reduces the temperature of PV cells, thereby increasing their efficiency. The experimental result showed that when used glazed collector in the system heat gain and thermal efficiency of the collector is extremely well. The BIPVT thermal 16 efficiency at varying with flow rate .increase in Reynolds number that heat transfer from the PV cells was improved that means electrical efficiency increases marginally. Here fin efficiency of the tube also affected the collector efficiency. BIPVT thermal efficiency varied transmittance/ absorptance products when increased thermal properties of the cell that the reduction in electrical efficiency but thermal efficiency can be improved. Increased wind speed reduced in thermal efficiency was due to the decrease in the mean plate temperature caused by the heat loss to the environment conversely, however the electrical efficiency increases. BIPVT used into the walls or roofing structure of a building to act as an insulating layer and could provide greater opportunity for the used of renewable solar energy technologies. BIPVT used air layer acts as a passive insulating barrier. The BIPVT onto the building could result in a lower cost system. In this paper the author N. BENZ et al. (1998) developed an experiment setup to use special type of evacuated flat-plate standard base boiling collector manufacturer by Thermosolar Inc of German. Their experimental aims were first a stable steam supply from the evaporator at different collector slopes and power outputs as well as under different system pressures and boiling temperatures up to 6 bar and 150˚C.second was an efficient thermal insulation of the hot absorber plate against the collector casing to realized highest efficiencies and temperatures up realized to 150˚C, third was a collector construction which also satisfies economic criteria by avoiding cost intensive materials and which easily can be transferred in a series production. They were worked how the minimized the heat loss of a special type collector and output temperature get should be 100-150 ˚C. So they were reduced first the radiation losses. The standard absorber was replaced by a selectively coated copper absorber with an extremely low emissive TiNx Oy coating. Economical and technical aspects krypton was the best suited gas because of its low thermal conductivity and it was filled evacuated flat-plate. In addition the radiation losses were reduced to use aerogele and glass fibre. The higher thermal output, evacuated collectors have the advantage of longer lifetime compared to non evacuated collectors, because no humidity and condensation problems occur in the casing. Typical interior pressures in the evacuated collectors which economically 17 can be maintained lie between 10 and10 Pa. Although convection losses are suppressed, gas conduction remains fully developed yielding typical efficiencies of below 20% at 150˚C steam temperature. After that they newly constructed and tested an optimized evacuated flat plate collector delivering steam at temperatures up to 150˚C at efficiencies of nearly 50%. In this paper the author Bo-Ren Chen et al. (2009) developed a the two-phase closed thermosyphon solar water heater experimental setup and comprised a solar collector, a double-pipe heat exchanger, parallel-fin tubes inside the storage tank, and an energy storage tank. In experimental setup used five collector tubes with two check valves set on the upper region. The collector and the check valve were made of copper, and the transparent plate was made of transparent polycarbonate plastics. The storage tank was made up of 5 mm-thick plastic plates in which one row of parallel-fin tubes was mounted. The double-pipe heat exchanger combines with the solar collector and fin tubes to form the two-phase closed thermosyphon loop. Fifteen kg of pure water was used as energy storage material inside the storage tank. The working fluid of the thermosyphon is alcohol with a fill ratio of 40%. The insulation material outside the storage tank prevents heat loss during the experiment. The experiment was developed to investigate the long-term investigated experimentally the long-term thermal performance of a two-phase thermosyphon solar water heater and compares the results with the different heat transfer conventional systems like including natural convection, geyser boiling, nucleate boiling and film-wise condensation. Results showed that the proposed system achieves system characteristic efficiency 18% higher than that of the conventional systems by reducing heat loss for the two-phase thermosyphon solar water heater. In this paper the author Hamid El Qarnia (2009) was developed theoretical model based on the energy equations to predict the thermal behavior and performance of a solar latent heat storage unit consisted of a series of identical tubes embedded in the phase change material (PCM). The sensible heat storage Compared latent heat storage was favorable due to the high energy storage density of PCMs and isothermal phase transition during melting. In their application a solar collector is 18 coupled with a latent heat storage unit (LHSU) filled with PCM, and a heat transfer fluid (HTF) which circulates through a solar collector. A thermal behaviour and performance of a solar latent heat storage unit tested with three kinds of phase change materials as storage mediums was studied theoretically under the summer climatic conditions. Estimated optimum control parameters the thermal performance of the storage unit during discharging period was also studied under various mass flow rate of outgoing water from the storage unit. The analysis of the results obtained in this work shows that the use of n-octadecane as PCM was not beneficial because the outlet temperature of hot water was never greater than 28 °C. On the other hand with paraffin wax (P116) the outlet temperature of hot water varies within the range 36–47 °C but a part of the PCM remains liquid. The results also show that the stearic acid offers an acceptable range of the outlet temperature of hot water and fully discharge of the storage unit for an optimum mass flow rate of water (m=0.005 kg/s) and hence it is beneficial for the heating water application. Therefore, the selection of phase change material should be done carefully in order to produce hot water in acceptable range of temperature. In this paper the author A. El Fadar et al. (2009) studied on solar adsorption refrigerator. Their refrigerants satisfy the Montreal protocol on ozone layer depletion and the Kyoto protocol on global warming. To contribute to these researches, this paper presents a study of an activated carbon-ammonia adsorption system powered by solar energy, using the coupling of a water-stainless steel heat pipe and a parabolic trough collector. In their paper the experimental setup proposed refrigerator comprises a solar collector, a condenser, an evaporator, refrigerant valves and a cylindrical adsorber containing the activated carbon-ammonia. The adsorption and desorption of the refrigerant are generated by alternate cooling and heating of the reactor. The evaporator end of the heat pipe was placed at the focused line of the PTC, and the condenser was inserted in the adsorbent bed. The reflective surface of PTC focuses the solar direct radiation on the linear absorber. Solar radiation was converted to thermal energy which was absorbed at the HP evaporator section. This heat vaporized the working fluid (water) in this section. The resulting difference in pressure drives vapour from the evaporator to the condenser 19 where it was condensed and then the latent heat of vaporization was released to the heat sink. The capillary pressure generated by the wick drives the condensed liquid to the evaporator for re-evaporation. The objective of their studied was to show the feasibility of an adsorption refrigerating system driven by PTC solar collector, which was coupled with an annular heat pipe for transferring heat towards the adsorbent bed. A theoretical model and a numerical program have been developed, in order to evaluate the performance of the adsorption cooling machine. The numerical results show a great sensitivity of the performance coefficient of the machine to the radius of the adsorber and the aperture width of collector. In their studied main conclusions were collector configuration, there exists an optimal dimension of the reactor (optimal radius), the ranges investigated, the optimum performance of the system is COPs = 0.18, when the external radius of the adsorber and aperture width of the collector are 14.5 and 70 cm, respectively and PTC is a useful component, for improvement of the solar adsorption refrigeration systems. This system is more efficient and lighter when coupled with heat pipe. In this paper the author N. Molero Villar et al. (2009) discussed how increased the performance of solar flat plate collectors. So designed a model able to compare the efficiency of different types of solar collector and would serve as a design tool for selecting configurations and materials and improved the design. They developed a general model flexible enough to compare the thermal behavior of different configurations of low temperature collectors was presented. Heat balance of an absorber plate was absorbed solar radiation was transferred to the working fluid partially lost to the ambient and partially stored in the plate as a change of its internal energy. In the back insulation top surface insulation temperature imposed with plate. For the back surface of the insulation a convection radiation coefficient was used to couple the heat transfer with the ambient. The possibility of absorbent fluid with transparent plate was also included as well as the used of transparent insulation materials. The model was transient and three dimensional and allows the calculation of the temperature of components of the collector in any position. As a consequence of this flexibility the model was very useful in comparing configurations or abnormal operation conditions. In order to show the capabilities of 20 the developed model the collector performance when the flow rate in the risers was non uniform had been studied and compared with experimental data. The collector efficiency does not change appreciably even when the flow at the outer risers was 1.5 times the flow of the central one but the outlet temperatures for each tube are very dissimilar. In this paper the author Xinping Zhou et al. (2009) discussed their paper producing energy from solar chimney thermal power system. The novel concept consists of a design for constructing a giant solar collector surrounding a hollow space excavated in a mountain in a steady-geology region. They had been done a model by comparing the data calculated for the model with the measurements in the only pilot prototype plant. Measurements including global solar radiations air temperature raised and velocities were used to calculate the collector efficiency in the model. After they were come into some conclusion those were a mountain hollow used as chimney avoids the use of considerable construction materials and thus saves considerable resources. The use of an existing undeveloped mountain eliminates the need to purchase large areas of land for a solar power site. The performance of this system was increased linearly energy production with increasing solar radiation. Energy production increased with increasing effective collector diameter. The proposed system that had been developed farther study was unique in the field of power generation and was appropriate for any mountain with enough large area at the foot in any place. Thus the combined power plant with any chimney height can undoubtedly be built as long as a mountain with enough elevation and large foot area can be found. It effectively use undeveloped mountains avoids the safety issues faced by the reinforced concrete chimney save a great amount of construction materials and reduced the energy cost in a long term to less than that of clean coal power plants even to less than that of conventional coal power plants increasing year by year. In this paper the author C.D. Ho et al. (2009) was discussed the performance with the help of Mathematical formulation after they done an experimental setup for watched the practical performance of the baffled double-pass flat plate solar air 21 heaters. The experimental results and theoretical prediction was good. The collector efficiencies increase with increasing recycle ratio and mass flow rate but slightly decrease with increasing incident solar radiation. The heat-transfer coefficient increases with increasing mass flow rate and recycle ratio owing to the fluid velocity enlargement resulting in increasing the collector efficiency. The hydraulic dissipated energy as well as increment of both power consumption and useful energy gain in operating baffled double-pass solar air heaters with external recycle internal fins attached are investigated with mass flow rate and recycle ratio as parameters. The magnitude of power consumption increment of baffled solar air heater is greater than that of the useful energy gain increment under the higher mass flow rate and recycle ratio. The proposed baffled double-pass solar air heater was profitable for operating under the lower mass flow rate and recycle ratio. They concluded the performance of baffled double-pass solar air heaters with external recycle and attached internal fins attached was investigated theoretically and experimentally considering the hydraulic dissipated energy. The advantages of baffled solar air heater were created higher turbulence and extending the heat-transfer area and thus the heat-transfer coefficient is enhanced. Although increasing the mass flow rate and recycle ratio are beneficial to collector efficiency improvement higher energy dissipation occurs at the same time when operating at a higher mass flow rate and recycle ratio. In this paper the author M.J. Montes et al. (2009) discussed parabolic trough solar thermal power plants connected to the electricity grid are based on oil as heat transfer fluid in the collectors. Performance was done as per all the solar multiples considered the yearly electricity production had been calculated. Variability of beam solar radiation was presented in five minutes interval data so next calculations are based on this working time interval. Strategy is different for a clear or a cloudy day. For both cases before the power plant was coupled to the grid the solar thermal power produced was stored in the system specifically designed to that purpose. To finish the economic study it observed that the levelized electricity cost increases as solar multiple increases because the investment cost was the most important factor in the calculation of this parameter. Simulations presented in this work are based on 22 a reference 50 MWe DSG plant with thermal storage and auxiliary natural gasboiler. Characterized by the solar multiple had been obtained for two type days: a clear day and a cloudy day. In order to estimate the yearly parameters for every solar multiple considered, a weight average had been calculated, taken into account the monthly percentage of clear, cloudy and overcast days. This method of assessing the annual plant performance, used only one clear day and one cloudy day in every month can be applied for sites where only limited meteorological data are available. It can be observed that levelized cost of electricity was greater as the solar multiple of the power plant increases, mainly owing to the great investment cost in the solar field. it was important to point out that the annual fuel consumption was reduced for a solar multiple increase because the thermal power fractions from the solar field and the storage become greater. The main disadvantage of this technology was the maximum power block inlet temperature which was limited to the oil upper working temperature in order to guarantee this fluid thermal stability. In this paper the author A. El Fadar et al. (2009) were done numerical study of a continuous adsorption refrigeration system consisting of two adsorbent beds and powered by parabolic trough solar collector (PTC). Their aimed of the current work was to present a novel system, in which the solar parabolic trough collector had been introduced to the adsorption refrigeration purpose in order to achieve continuous cycles using two adsorbent beds. A computational program was developed in order to simulate the behavior of the solar adsorption refrigeration system and to optimize its performance. Through the analysis results a number of conclusions can be drawn as follows: 1. it was found that the variations of the adsorbent bed thickness affects the specific cooling power more than the cycle COPS On the other hand, it was put in evidence that the increase in the heat source temperature would result in an increase in cycle COP, solar COP and specific cooling power. 2. Within the ranges of investigation, simulation results show that the values of optimal performance are obtained at heat source temperatures between 80 and 100˚C, with small radial bed thickness (10–30 mm) and in the range 15–30 m3 for hot water storage tank. 3. Due to its high efficiency, the parabolic trough collector could make possible the achievement of continuous operation of the 23 adsorption system. The obtained results demonstrated the possibility to produce cooling for a long period in a sunny day and, hence to overcome the intermittent character of solar adsorption refrigeration systems. In this paper the author S. Janjai et al. (2000) was developed a simulation model of a large area plastic collector and used as a tool for investigating the performance of the collector. They developed a low cost large area plastic solar collector using a plastic water bag to collect solar energy. The main structure of this collector comprises three basic components, mainly a plastic bag, a UV-stabilized plastic sheet cover and an insulated floor. The top layer of the bag is made of a transparent plastic sheet and the bottom layer was made of a black plastic sheet to absorb solar radiation. The insulated floor was made of plastic foam sandwiched between two metal sheets. Plastic materials were used in order to reduce the investment cost of the collector. The different modes of heat transfer occurring in the collector were schematically Incident solar radiation was first transmitted through the plastic cover then the top layer of the water bag , the water in the bag and finally to the bottom layer of the bag . The incident radiation was mainly absorbed by the bottom layer of the water bag and the water inside the bag. The various modes of heat transfer in the collector are summarized as follows: forced convection heat transfer between the bottom layer of the bag and the water between the top layer of the bag and the water and the wind-related convection heat loss from the plastic cover to the ambient air convection heat transfer in the air gap between the top layer of the bag and the plastic cover, heat loss through the insulated floor to ambient air and long wave thermal radiation heat exchange between the water and the sky, between the water and the plastic cover, between the top layer of the bag and the sky, between the top layer of the bag and the plastic cover, and between the plastic cover and the sky. These thermal radiation exchanges between water in the bag and the sky were taken into account because the plastic cover cannot completely protect against long wave radiation losses. Increase in water depth decreases the outlet water temperature. It was found that the outlet water temperature was not sensitive to wind speed. 24 1.3 Object & Scope of Work Objective of the present work is to evaluate the performance of evacuated tube collector based solar water heating system. Various design parameters such as storage tank volume, the water volume in the ETC tube is studied in details to find its impact on the system performance. The scope for the work involves 1. Evaluated a percentage efficiency of ETC based solar water heating system under day test condition as mentioned by MNRE. 2. Compare the data to evaluate the system efficiency under alternet time constant 2,5,10 minute respectively. 3. To study the impact of the storage tank volume with reference to collector area. 4. Study on volume measurement processudure and recommend the suitable one . 25 Chapter 2 Solar Radiation and Geometry 26 2.1 Introduction Solar radiation is a perpetual natural energy source that, along with other sources of renewable energy has a great potential for a wide variety of applications because of its abundance and accessibility. In order to study the impact of solar radiation on the Earth, it is necessary to determine the amount of energy reaching the Earth’s surface. The average energy density of solar radiation just above the Earth’s atmosphere in a plane perpendicular to the rays is 1367 W/m2, a value called the Solar Constant. This radiation from the Sun is partially depleted and attenuated as it traverses through the atmospheric layers preventing a substantial portion of it to reach the earth’s surface. This phenomenon is mainly due to absorption, scattering and reflection. Solar Radiation is also unevenly distributed though out the world because of variables such as solar altitude, seasons, atmospheric conditions, cloud coverage and degree of suspended particle present in air. 2.2 Solar Geometry . Figure 2.1 (A) Figure2.1 (B) Figure 2.1 (A) Slope, surface azimuth angle, solar azimuth angle, zenith angle and altitude angle for a tilted surface. (B) Plane view showing solar azimuth angle. 27 In reference to the Figure 2.1 the important angles needed to find the solar radiation on any particular plane are discussed below. Latitude (φ φ) The latitude φ of a location on the surface of the earth is the angle made by the radial line joining the location to the center of the earth with the projection of the line on the equatorial plane. Declination Angle (δ) The declination δ is the angle made by the line joining the centers of the sun and the earth with its projection on the equatorial plane. The following simple relation is used for calculating declination angle δ (in degree) = 23.45 sin [360(284+n)/365] (2.1) where, n indicates the day of the year. Tilt Angle (β) The slope or tilt angle β is the angle between the plane of surface in question and the horizontal. Surface Azimuth Angle (γ) This is the angle made in the horizontal plane between the line due south and the projection of the normal to the surface on the horizontal plane. Hour Angle (ω) The hour angle ω is the angular displacement by of the sun east or west of the local meridian duo to rotation of the earth on its axis at 15 degree per hour. Incidence Angle (θ) The incidence angle θ is the angle between the incident beam radiation on any plane surface and the normal to the surface. The incidence angle θ is a function of φ, δ, γ, ω and β which is represented by the following equation cos θ = sin φ (sinδcos β + cosδsinβ cosγ cos ω)+ cos φ (cosδ cosω cos β -sin δcos γ sin β) + cos δ sin γ sin ω sin β (2.2) 28 Zenith Angle (θz) This is the angle of incidence beam radiation on the horizontal surface. It is obtained from the equation 2.2 where β approaches zero. cos θz = cos φ cos δ cos ω + sin φ sin δ (2.3) Solar Altitude Angle (α αs) The solar altitude angle αs is the angle between the horizontal and line to the sun i.e., the complement of the zenith angle. Solar Azimuth Angle (γs) The solar azimuth angle γs is the angle made by in the horizontal plane between the line due south and the projection of the line of sight of the sun. It is represented in the form cos γs = (cos θz sin φ – sin δ)/ sin θz cos φ (2.4) Incidence angle θ can also be determined in terms of zenith and solar azimuth angle cos θ = cos θz cos β + sin θz sin β cos (γ-γs) (2.5) Sunrise, Sunset and Day Length The sunrise and sunset hour angle is obtained from the Equation 2.3 by substituting zenith angle θz approaching 90º . ωs = cos-1 (-tan φ tan δ) (2.6) The positive value of ωs, given by Equation 2.6 corresponds to sunrise and the negative value to sunset. Since 15º of the hour angle is equivalent to 1 hour, the corresponding day length (in hours) is given by Smax = 2/15 cos-1 (-tan φ tan δ) (2.7) Solar Time and Equation of Time Solar time is based on the fact that when the Sun reaches its highest point in the sky, it is noon. Apparent solar time is based on the apparent solar day, which is the interval between two successive returns of the Sun to the local meridian. The solar time does not coincide with local clock time and the standard time can be converted to solar time by applying two corrections. The first correction is a constant correction arising due to the difference in longitude of a location and the meridian on which the standard time is based. The second one, termed equation of time is because of 29 small fluctuations in earth’s orbit and rate of rotation. The relationship between solar time and standard time is represented in the form Solar time = Standard time ±4 (Standard time longitude – Longitude of the location) + Equation of time correction (E) (2.8) The positive sign in the first correction is applicable for the western hemisphere and the negative sign is for eastern hemisphere. Equation of time (in minutes) correction is determined by the Equation 2.9 or from equation of time vs. month graph based on experimental observations. Figure 2.2 shows the equation of time for the year 1996. E = 229.2(0.000075 + 0.001868 cos B – 0.032077 sinB–0.014615 cos2B–0.04089 sin2B) where, (2.9.a) B = (n-1)(360/365) (2.9.b) Figure 2.2 The Equation Of Time E In Minute As A Function Of Time Of Year The horizontal axis measures the months of the year; the vertical axis measures the difference in minutes between the true solar time and the mean solar time. It can be noted that the two times are equal four times a year and that the difference has a minor amplitude swing in the period spring-summer and a major amplitude swing in the period fall-winter. The local solar noon at a place can be determined from the following equation Local Solar noon = 12 – Equation of time ± (longitude of reference meridian – observer’s longitude) /15 (2.10) 30 Table 2.1 Unit And Range Of Some Quantity Related To Solar Geometry. Quantity/Symbol Unit Range Day of year (N) Day 0 to 365 Latitude (φ) Degree -90(south pole) to +90(north pole) Longitude Degree -180(East) to +180(West) Declination angle (δ) Degree -23.44 to +23.44 Tilt angle (β) Degree 0 to 180 Surface azimuth angle (γ) Degree -180(north) clockwise to +180 Hour angle (ω) Degree -180 (midnight), clockwise to +180 Incidence angle (θ) Degree 0 to 90 Zenith angle (θz) Degree 0 to 90 Solar altitude angle (αs) Degree 0 (horiz) to 90 (vert.) Solar azimuth angle (γs) Degree -180(north) clockwise to +180 Profile angle Degree 0 to 90 Equation of time Minute -16 to 16 Local Mean Time h:min:s 0 to 24 or 12 a.m. to 12p.m. 2.3 Solar Radiation on a Surface The position of the sun relative to the surface of the earth must be known for the determination of the incoming solar radiation falling on any surface. The incident solar flux falling on the surface of a building is observed to be time dependent phenomenon. Therefore the sun path geometry plays a vital role in determining the magnitude of the solar radiation coming on the earth’s surface. 2.3.1 Components of Radiation on a Surface Solar radiation incident on any surface can be classified into three parts. 1. Beam radiation (Ib) 2. Diffused radiation (Id) 3. Global radiation (Ig) The total solar flux incident on any tilted surface is the sum of the beam and diffuse radiation falling directly on the surface and the radiation reflected onto the surface from the surrounding. 31 2.3.1.1 Beam Radiation on a Surface The part of the incident solar radiation, which comes directly from the sun, without reflection from other objects, is called beam or direct radiation. This radiation is received from the sun without any change in direction. The direct solar radiation, which is falling on the tilted surface, is given by Ibt = IbhRb (2.11) where Ibh is beam radiation on the horizontal surface, and Rb is the tilt factor for beam radiation. The tilt factor for beam radiation is defined as the ratio of beam radiation flux falling on a tilted surface to that falling on a horizontal surface. The incident angle on the horizontal surface is obtained from Equation 2.3 where the incident angle becomes the zenith angle. Similarly, for any tilted surface, the incident angle is given by Equation 2.2 or Equation 2.5. Therefore, the incident beam radiation on horizontal surface is Ibh = Ibn cos θz (2.12) Where Ibn is beam radiation in the direction of ray. And the component of beam radiation falling on a tilted surface having a surface azimuth angle γs is expressed as Ibt = Ibh [cos β + sin β tan θz tan (γs -γ)] (2.13) For Vertical surface (i.e. β = 90º), the incident beam radiation is Ibv = Ibh [tan θz cos (γ - γs)] (2.14) Therefore, it is evident that the magnitude of solar beam radiation falling on the surface depends on the orientation of the surface, i.e. azimuth angle of the surface. 2.3.1.2 Diffuse Radiation on a Surface Due to the presence of cloud , water particles , dust etc. a part of solar radiation is scattered while passing through the atmospheric boundary layer. Diffuse radiation is the component of the solar radiation, received from the sun after it is distracted from original direction. The diffuse solar radiation, which is falling on the tilted surface is given by Idt = IdhRd (2.15) Where Rb is the tilt factor for diffuse radiation. 32 The tilt factor for diffuse radiation is defined as the ratio of diffuse radiation flux falling on a tilted surface to that falling on a horizontal surface. Here assuming that the sky is an isotropic source of diffuse radiation, a tilted surface at slope β from the horizontal has a view factor to the sky (1+ cos β )/2 and this is also equal to tilt factor for diffuse radiation i.e. Rd = (1+ cos β )/2 (2.16) 2.3.1.3 Global Radiation on a Surface The global or total radiation flux It on a tilted surface is It = IbhRb + IdhRd + (Ibh + Idh)Rr (2.18) The amount of global radiation on a given surface varies continuously with the movement of the sun, because the incident angle changes with the sun’s position throughout the day. Thus the global radiation is a function of zenith angle and azimuth angle. Now if we introduce the tilt factors, the Equation 2.18 is modified as It = Ibh[cos β + sinβtan θz cos(γ - γs)] +Idh(1 + cosβ)/2+(Ibh+Idh)ρg(1- cos β)/2 (2.19) For horizontal surface (β=00), i.e. for roof of the building the incident solar radiation flux is It = Ibh + Idh (2.20) for vertical surface (β=900), i.e. for any wall of the building having a surface azimuth angle γ the incident solar radiation is It = Ibh[tan θz cos (γ - γs)] + Idh/2 + ρg (Ibh + Idh) /2 (2.21) 2.3.2 Reflected Radiation on a Surface Since (1+ cos β )/2 is the radiation view factor for a tilted surface with respect to the sky, it follows that (1- cos β )/2 is the radiation view factor for that tilted surface with respect to the surroundings (assuming that the radiation of the beam and diffuse radiations falling on the ground is diffuse and isotropic). If the surroundings have a diffuse reflectance of ρg for the total solar radiation, the tilt factor for reflected radiation is given by Rr = ρg (1- cos β )/2 (2.17) 33 Chapter 3 Evacuated Tube Collector 34 3.1 Introduction Solar energy is one of the most promising alternatives among the renewable energy sources. Our aim is to utilize this energy from to carry out useful works. Evacuated tube collector is one of the major area in which large scale exploration of solar energy can be achieved. This leads to large saving in conventional energy. They are clean and green and thus reflect the commitment for preservation of environment. Solar heater is a device which is used for heating the water for domestic and industrial purposes by utilizing the solar energy. Solar energy is the energy which is received from the sun in the form of solar radiations. When these solar radiations fall on absorbing surface, the surfaces absorbs the visible radiation and converts it to heat for heating the water. When numbers of evacuated tubes are used for heating the water then solar heater is called evacuated tube solar water heater. Although there are many type of solar water heater like flat plate solar water heater, evacuated tube solar water heater, concentrated solar water heater. Flat plate solar water heaters are being used from earlier days. Concentrated solar water heaters are used when we need to generate high temperature steam. But in this chapter we would concern only with evacuated tube collectors. Evacuated tube solar collectors are very efficient and can achieve very higher temperatures. 3.2 Working Principle Figure3.1 Water heating in Evacuated Glass Tube 35 The working of evacuated solar water heater is based on a principle of thermo siphon as shown in figure 3.1. The key important point of these systems is that the storage tank is always located higher than the collector. The solar radiation after passing through outer glass tubes fall on the inner glass tubes which are coated with absorbent materials. So these solar radiations are absorbed by the absorbent materials in the inner tube and get converted in to heat after absorption. Due to absorption, surface of inner tubes gets heated up and this heat is transferred to the water exist inside the inner tubes. The temperature of the water in the tubes rises making it less dense or lighter and hot. This lighter water naturally moves up to the top of collector and goes to the storage tank. This makes the colder and heavier water in water tank moves down to the bottom of the collector. That continuous displacement occurs naturally. So the users can get the hot water (30 - 90°C) from the tank. 3.3 Types of Evacuated Tube Collectors 1. Direct-flow evacuated-tube collectors 2. Evacuated heat pipe tubes collectors 3.3.1 Direct-flow evacuated-tube collectors A B Figure: 3.2 A & B Direct-flow evacuated-tube collectors Evacuated tube collectors have multiple evacuated borosilicate glass tubes which heat up solar absorbers and solar working fluid. The vacuum within the evacuated tubes reduce convection and conduction heat losses direct-flow evacuated tube 36 collector has two pipes that run down and back inside the tube. One pipe is for inlet fluid and the other for outlet fluid. Since the fluid flows into and out of each tube. The basic construction of Direct-flow evacuated tube collectors is show in figure 3.2.A and figure 3.2.B. 3.3.2 Heat pipe evacuated-tube collectors Figure 3.3 Evacuated Heat Pipe Tubes Collectors Heat pipe evacuated tube collectors contain a copper heat pipe which is attached to an absorber plate inside a vacuum sealed solar tube. The heat pipe is hollow and the space inside is also evacuated. Inside the heat pipe is a small quantity of liquid such as alcohol or purified water plus special additives. The vacuum enables the liquid to boil at lower temperatures than it would at normal atmospheric pressure. When solar radiations falls the surface of the absorber the liquid in the heat tube quickly turns to hot vapor and rises to the top of the pipe. Water or glycol flows through a manifold and picks up the heat. The fluid in the heat pipe condenses and flows back down the tube. This process continues as long as the sun shines. The basic construction of Heat pipe evacuated-tube collectors is show in figure 3.1. 37 3.4 Basic Working Principle of Heat Pipe ETC 1. Vacuum Tube 2. Heat Pipe 3. Cold Liquid 4. Hot Vapor 5. Absorber 6. Collector Return (Hot) 7. Collector Supply (Cold) 8. Heat Exchanger (condenser) 9. Shock Absorber Figure 3.4 Different Parts of Heat Pipe Evacuated Tube Collector The high temperature operation of Evacuated Heat Pipe Tubes (EHPT) and their very low radiant heat losses make them ideal for solar water heating solar, space heating and industrial process heating applications. The tubular iron free cover glass tube and vacuum within protect the absorber coating and all structure materials from corrosion and adverse weather conditions. The vacuum tube envelope minimizes heat loss and ensures high collector durability and steady performance. The heat pipe is an evaporating condensing device for rapid heat transfer. The latent heat of vaporization is transferred by means of evaporating a water based liquid in the solar heat inlet region and condensing its vapor in the discharge region. The heat source is the absorber plate that is continuously bonded to the heat pipe. The condenser (heat discharge region of the heat pipe) is in direct contact with a manifold which serves as a heat exchange (sink). In addition the heat 38 pipe has a diode function heat transfer is always in one direction from absorber to the manifold (thus collector to storage tank) and never the reverse. Firstly the hot vapor stream from the evaporating region to the condenser is constrained. Secondly the condensed heat transfer fluid is partially captured in the condenser. As a result the amount of effective heat transfer fluid inside the heat pipe is proportionally reduced. 3.5 Technology of Eliminating Different Problems to Optimize the Design of Heat Pipe ETC 3.5.1 Heat Pipe Critical Temperature One technique to limit the maximum operating temperature of the Tube is to select a heat pipe fluid with suitable physical properties and correct quantity. This causes the heat pipe to contain only vapor (no fluid) at the critical point, causing the heat transfers mechanism to stop. In the newly developed Memotron tube the maximum working temperature is controlled by means of a memory metal spring (thermo dynamic valve) that is positioned inside the heat-pipe's condenser. The valve adjusts the heat flux of the heat pipe to a minimum level when the operation temperature approaches its limit. The memory metal is programmed to change its shape at a pre-set temperature. This allows for the condenser fluid to be retained inside the condenser. When the programmed temperature has been achieved the memory metal spring expands and pushes a plug against the neck of the heat pipe blocking the return of the condensed fluid and stopping heat transfer. 3.5.2 High Vacuum Sealing The major interest in evacuated solar collectors is that the vacuum (10 –5 Torr) essentially eliminates conduction and convection losses. The vacuum chamber being the best possible insulation for a solar collector suppresses heat losses and also protects the absorber plate from external adverse conditions. This results in exceptional performance far superior to any other type of solar collector. Due to the atmospheric pressure and technical problems related to the sealing of the collector casing the construction of an evacuated flat-plate collector is extremely difficult. To overcome the enormous atmospheric pressure many internal supports for the transparent cover pane must be introduced. 39 3.5.2.1 Mechanical Evacuation Process The mass production of fluorescence light bulbs set a precedent for the tubular solar collector design. Building a tubular evacuated solar collector and maintaining of its high vacuum, similar to light bulbs and TV tubes, is a well-established production process. The ideal vacuum insulation of the tubular evacuated solar collector obtained by means of a suitable evacuating process has to be maintained during the 25+ years life of the device to reduce the thermal losses through the internal gaseous atmosphere (convection losses). 3.5.2.1 Chemical Evacuation Process The high vacuum of 10 –5 Torr is achieved by carefully preventing all the possible gas efflux from internal solid materials to the vacuum chamber. high vacuum level of the tube over a long time period is challenging. It has been found that numbers of evacuated solar collectors face the problem of vacuum degradation due to poor sealing techniques. Therefore highly reliable vacuum seals for the EHTP are key quality criteria as the seals withstand the thermal stress and temperature shocks. To absorb material out-gassing due to the high operational temperature the vacuum is maintained through a Barium getter inserted in the collector tube. The dose of Barium must be calculated for the targeted life cycle of the system. Tubes are designed to maintain their high vacuum for a period of 25-30 years under normal operation conditions. System stagnation reduces the life expectancy of tubes. 3.5.3 Thermal and Mechanical Shock Absorber Figure 3.5 A Flexible Neck System Absorbs both Thermal and Mechanical Shock Absorber 40 EHTP utilizes the matched glass-to-metal sealing technique to achieve hermetic high vacuum seals. The glass and alloys are carefully selected based on coefficients of thermal expansion. This thermal expansion match avoids stresses in the seal and maintains the integrity of the seal. In practice over the past 23 years of production it has been shown that the patented glass to metal seals are strong and durable. These seals form a bond layer which is elastic and tolerant to glass displacements during extreme temperature cycling. Figure 3.6 A Solar Heating System Using Heat Pipe ETC Figure 3.7 A Typical Photograph of Heat Exchanger Used in Heat Pipe ETC 41 3.6.1 Advantages of Evacuated Tube Collector • Evacuated tube solar collectors can collect the sun's energy from multiple angles. This is possible because of their 360º tubular design. When the sun is at lower angles it is almost impossible for typical solar collectors to trap the solar energy. This is not the case with evacuated solar collectors. They are built with a broader collector area so as to allow maximum utilization of the sun's energy. • Air is evacuated from the solar tube to form a vacuum. This greatly reduces conductive and convective heat loss from the interior of the tube. As a result wind and cold temperatures have less effect on the efficiency of the evacuated tube collector. • Due to the high efficiency absorption of solar radiation even during overcast conditions combined with excellent insulative properties of the solar tube solar tube collectors can heat water all year round (backup from gas and electricity is still required). • Evacuated tube solar water heaters work more efficiently in mid morning and mid afternoon. For places with freezing climates evacuated solar collectors are able to maintain a temperature in the range of 75ºC to 175ºC. Their operation is not affected by rising or falling temperatures. This property makes these solar heaters ideal for places with cold climate. • Evacuated tube solar collectors require lesser space and the collectors are easy to install. Emission of carbon dioxide is also maintained at a lower level. Replacement of the damaged tubes is possible lest there should be any flaw in the system. Due to the vacuum created, the tubes do not get hot. Evacuated tube solar water heater promises a durability of at least twenty years with minimal maintenance. 3.6.2 Disadvantages of Evacuated Tube Collector • As they are not insulated, a large part of the absorbed heat is lost particularly under windy and cool weather conditions. 42 • They are very efficient at low output temperatures but, because they are subject to a high heat factor loss their efficiency declines dramatically as the output temperature increases. • Evacuated tube collectors are more cost effective in cold or cloudy climates and are cost effective for high-fraction contribution to water heating energy. 3.7 Evacuated Tube Vs Flat Plate Technology • Evacuated tube technology captures sunlight better than flat plate systems because tubes maintain a greater surface area during the movement of the heater in relation to the sun. The net benefit is more hot water over a longer daily period. • Evacuated tubes are more efficient at transferring heat as there is considerably less heat loss because of the vacuum between the tubes. • Evacuated tube collectors can be used in subzero temperatures without the system sustaining damage. Flat plate systems often require expensive and complicated "antifreeze" systems to be installed. • Evacuated tubes are strong, long lasting and should one be broken inexpensive and easy to replace. • To reduce the cost of flat plate prices various manufacturers have changed the material of the collector from copper to steel. They then need to use corrosion inhibitors to stop rusting. • Another major disadvantage of flat plate is they suffer from condensation collecting on the inside of the glass. It is found that most of the flat plate systems become completely opaque after a few years of operation. • In evacuated tubes system to keep the tank as close as possible to reduce cost and maintain efficiency. • In evacuated tubes system tank is placed above the collector to use the thermosyphon principal and hence no pump is required. • The flat plate systems that are prone to freezing use anti freeze and the water therefore cannot go directly into the tank but must pass through a coil inside the tank. This increases cost. 43 Chapter 4 Experimental Procedure and Setup 44 4.1 Introduction The test method is based on a lumped capacitance model, where it is assumed that average water temperature in the storage tank characterizes the behaviour of the whole system whether the storage is well – mixed or stratified. The test procedure envisages characterizing the thermal performance of the system without any withdrawal of hot water from the storage tank. This strategy is adopted because the performance of the solar water heating system strongly depend son the pattern of withdrawal of hot water from the storage tank, and there could be wide variation in the withdrawal pattern. The system performance is evaluated in two parts corresponding to its performance during daytime and separately during nighttime. Usually, the storage tank in solar water heating systems which are designed to work on the principle of thermosyphonic flow is located at higher level than the top edge of the solar collector with a view to suppress reverse flow during night. In such a case, the solar collector and part of piping would not play role in loosing heat from the tank during night as it does during the day. However, night time test would account for all thermal losses from the system. 4.2 Day-Time Performance The following energy balance equation would determine the thermal performance of the solar hot water system during the day-time Rate of change in  Rate at which useful  Rate at which energy  energy contents of  energy is supplied to  is lost from water in   = −  the water in the   water in the storage  the storage tank to        storage tank  tank by solar collector  the ambient air  (4.1) Mathematically, this may be expressed as follows: (MC)s dTs = AaF' [GT(τα )eff − UL(Ts − Ta)] − (AsUs + ApUp )(Ts − Ta ) dt (4.2) Rearranging and integrating equation (4.2) with respect to time, between the time period t1 to t2 during which the energy is collected, one gets t 2d t 2d (MC)s(Tsfd − Tsid) = AaF' ∫ GT(τα )eff , dt − (AaF' UL + AsUs + ApUp ) ∫ (Ts − Ta )dt t1d t1d (4.3) 45 The total energy incident on the collector during the time period from t1d to t2d is given by the following expression t 2d Qc = Ac ∫ GTdt t1d (4.4) Dividing equation (4.3) by equation (4.2), one gets ηsys = ηsys,0 − Usys, d.X (4.5) Where ηsys = (MC)s(Tsfd − Tsid) t 2d Ac ∫ GTdt t1d t 2d AaF' ∫ GT (τα )eff.dt t1d ηsys,0 = t 2d Ac ∫ GT.dt t1d AaF' UL + AsUs + ApUp Ac Usys, d = t2d ∫ (T X = t1d s (4.6a) (4.6b) (4.6c) − Ta )dt t 2d ∫ GTdt t1d (4.6d) The parameters ηsys,0 and Usys,d are defined as the characteristic parameters of the thermosyphonic solar water heating systems. 4.3 Night-Time Performance During night time, no solar radiation is received and also there is no flow of water through the solar collector. The heat is therefore lost primarily from the storage tank and part of the piping. In view of this, the equation (4.3) may be re-written as follows t 2n t 2n dTs = −(AsUs + Ap' Up ) ∫ dt t1n (Ts − Ta ) t1n (MC)s ∫ (4.7) 46 or   (MC)s ln Tsfn − Tan  = Usys, nAc(t 2n − t1n ) (4.8)  T sin− Tan  Where Usys, nAc = (AsUs + Ap' Up ) (4.8a) Cooling time constant to rate the performance of the solar water heating system during no-radiation period may be expressed by the following expression τcooling, n = (MC)s Usys, nAc (4.9) Here, the τcooling represents the time at which the difference between the hot water temperature in the tank and the mean ambient temperature drop to 36.8% of its initial value. Slope of the curve plotted between ln (Tsm - Tam ) with time gives the value of 1/τcooling, n. 4.4 Test Conditions The total duration required for one cycle of the daytime test is 7h, comprising 3.5h before solar noon and 3.5 h after solar noon. The total solar irradiance during the test duration of 7h shall be greater than or equal to 14 MJ/m2. The ratio of solar irradiation in the forenoon and afternoon periods, each of 3.5h, shall lie in between 0.5 and 1.5. The average value of wind speed during the test period shall be less than 4 m/s. 4.5 Experimental Determination Thermal performance of the thermo-syphon domestic solar hot water system shall be characterized by three parameters viz. ηsys,o Usys,d and τcooling,n under this test procedure. The testing of the system shall be carried out in two steps, namely, the solar test (day-test) and the no-solar test (night-test). As the present test procedure proposes tests under conditions of no-load withdrawal, the performance thus obtained may be treated as the lower limit of the performance. 47 Figure 4.1 Schematic Diagram of the Experimental Set A schematic sketch of test-up is given in Fig: 4.1. The main components of the test set –up are as follows. • Domestic solar water heating system, as installed by the manufacturer, consisting of solar collector(s), storage tank, inter-connecting piping, and supporting stand. • Provision of cold water supply. • A hydraulic loop integrated with the test set-up, consisting of a circulating pump (capacity > 40 lpm) for mixing the water, one Rota meter to measure water circulation rate, a hydraulic pressure source, bleed valve, pressure gauge, and other accessories. • Measurement system, which shall include a computer based data logging systems, instruments / sensors for measuring solar radiation on the plane of solar collector, ambient air temperature in the vicinity of test set-up, air velocity on the plane of solar collector, and pressure gauge, along with necessary fixtures for their installation • A white opaque shade to cover the collector system as per requirement. 48 4.6 Measurements of Physical Specifications All physical measurements, such as, length, width, thickness, etc. shall be measured and reported in mm. Gross area of solar collector is defined as the total area on which solar radiation is falling (taking into account the gap, if any, between the tubes, and also the frame etc.). For flat plate solar collectors, it shall be calculated by multiplying width and length of the collector measured from outer edge to the outer edge. For the solar water heating models using all-glass ETCs, length shall be measured from bottom side of the storage tank to the outer edge of bottom tube holder while width shall be taken as equal to the length of the bottom tube holder. The measurement accuracy of the gross area shall be ± 0.1 %. The volume of the storage tank shall be measured to an accuracy of ± 1%. 4.6.1 Measurements of Climatic Parameters Solar radiation shall be measured using a class-I Pyranometer on the plane of solar collector. For this, a mounting stand shall be used. For measuring ambient air temperature, the measuring sensor (a calibrated RTD) shall be located shaded by a Stevenson screen in the vicinity of the test set-up (not more than 10 m from it. It shall be ensured that there is no obstruction by any structure or building to alter (block or enhance) the free flow of the natural wind to the sensor. The outside surface of the Stevenson screen shall be of light colour, preferably white, and its bottom shall be kept at least 1 m above the ground level. The surrounding air speed shall be measured on the collector surface at about its middle every half an hour with an accuracy of ±0.1 m/s and the average value of the day will be reported along with the test results. 4.6.2 Measurements of Performance Parameters The duly calibrated RTDs shall be used for measurement of water temperature. The accuracy of measurement shall be ± 0.1ºC or better. Measurements shall be made at two locations in the storage water tank. For this, measuring sensors shall be inserted through the openings provided by the manufacturer for inlet / outlet of water ensuring that • Sensor reaches about middle of the tank. 49 • Tip of the sensor remains in the water. • The sensor does not touch the walls of the storage tank. The pressure shall be measured to an accuracy of 5% of actual reading. Elapsed time measurement shall be made to an accuracy of ± 0.2%. Computer based systems shall be used for data monitoring and logging. Analog or digital recorders shall have accuracy equal to or better than ± 0.5 % of the full-scale reading and have a time constant of 1 s or less. The peak signal indication shall be between 50% and 100% of full scale. 4.7 Pre-Conditioning Test Fully assembled system filled with water shall be kept exposed to weather conditions for 15 days having daily solar irradiation on the plane of solar collectors more than 16 MJ/m2. The days with solar irradiance lesser than this value shall not be counted. After pre-conditioning of fifteen days, all parts of the system shall be inspected for any visual sign of degradation, deformation, ingress of moisture/dust, etc. and shall be reported. 4.8 Static Pressure Leakage Test The purpose of this test is to ensure the integrity of Solar Hot Water System particularly its tank to withstand the pressure, which it might meet in service. Initially, air bleed valve is kept open. For solar water heating systems using flat plate collectors, it is to be ensured that all air is removed from the collector by circulating water though it. Thereafter, the solar water heating system (tank + collector), using flat plate or evacuated tube collectors, is filled to its full capacity (as per claims of the manufacturer) with water at a temperature of 60 ± 2ºC. After filling, the bleed valve and all other valves are closed, and specified hydraulic pressure is applied. For flat plate collector systems, the specified pressure is 5.0 kg/ cm2 while for ETC based systems it is 0.2 kg/cm2. The system is kept pressurized for a period of 30 min. All parts of the system, especially the storage tank, shall be inspected for visual sign of leakages. Results of the test in terms of the initial and final reading of the 50 pressure gauge, temperature of the water, duration of the test and the result of inspection shall be reported. 4.9 Day Time Test • Determine solar noon for the day of test and also the corresponding Indian Standard Time (IST). • Solar collector is shaded completely with an opaque cover, white on the top exterior, at about 4 h before the solar noon. The storage tank of the solar water heating system is filled fully with water. The quantity of water filled in the storage tank only shall be taken as notional capacity of the solar water heating system. • The water in the storage tank is fully mixed by switching on pump for 5 minutes before beginning of the test at the designated time instant. • Initial value of the storage water temperature, Tsid is measured and recorded, and the shade-cover is removed at 3 h 30 min before the solar noon. • Measurements for ambient air temperature, water temperature of the storage tank, and solar irradiance on the plane of solar collector get commenced at the start of the test. The measurements are continued subsequently for the entire period of the test at an interval of one minute or less, however, recording of data is adequate at an interval of 10 minutes. • To end the day-test cycle, the solar collector is again shaded on expiry of 3h 30 min from solar noontime. The water in the storage tank is again mixed by operating the pump for five minutes, and final storage water temperature (Tsfd) is measured and recorded. • The test is repeated for at least ten days with different values of initial storage water temperature. The first test shall be carried out with cold (supply) water in the storage tank. For subsequent days, initial water temperature shall be raised in uniform steps to cover up to 70ºC temperature (fully mixed storage). • Different initial temperature in the storage tank may be achieved by adding appropriate quantity of cold water to the previous day’s heated water in the 51 storage tank. Alternatively, hot water from any other source may also be used to achieve the required temperature of the water in the storage tank. • The minimum solar irradiance on the plane of solar collector, GT, during the period of day-test shall be 550 W/m2 and the ratio of minimum solar irradiance to maximum solar irradiance recorded during the day-test should not be less than 0.5. The data for the days for which these conditions are not specified, will not be used in the estimation of ηsys, o and Usys, d. 4.10 Night Time Test Night time test essentially intends to find out overnight heat loss characteristics of the solar system. The duration of test is 10 h under no-solar conditions. The following steps are undertaken to perform this test • Measure the amount of solar radiation falling on the plane of solar collector (s) before starting the night-test; if the measured value is more than 50 W/m2, cover the solar collector (s) by an opaque shield. This may be done by fixing the cover leaving a, gap of about 0.5 m above the solar collector(s) to allow free flow of surrounding air. After the solar radiation falls below the value of 50 W/m2, the cover should be removed. • Switch on the mixing pump for about 5 minutes before the start of night test time so that water temperature in the storage tank is fully mixed and attains uniform temperature. Undertake measurement of initial storage water temperature, Tsin. • Carry out measurements of water temperature of storage tank, and ambient air temperature at an interval of fifteen minutes during the test period. • Again, switch on the mixing pump at the end of test period of for about 5 minutes and measure final storage water temperature, Tsfn. • Repeat the experiments for number of days for which the day-test was performed. 52 4.11 Instrument Used In the Experimental Setup The instruments that have been used for this experiment are briefly discuss below 4.11.1 Resistance thermometer (RTDs) The resistance of certain metals changes with temperature change. Resistance thermometer utilizes this characteristic. With the increase of temperature, the electrical resistance of certain metal increase in direct proportion to the rise of temperature. Therefore if the electrical resistance of a wire of knows and calibrated material is measure, the temperature of the wire can be determined. Platinum, copper and nickel are generally used in resistance thermometer. In this type of thermometer, a temperature sensitive resistance element is fabricated in a suitable from to insert in the medium whose temperature is to be measured, and is connected by leads to a whetstone bridge as shown in fig: 4.2.the bridge consists of a sensing element resistance X having high temperature coefficient and resistance A, B and C whose ohmic values do not alter with change of temperature.LR1 and LR2 are the lead wire resistance of the sensing element. The principle of wheat-stone bridge states that in balance condition (when no current flows through galvanometer), the ratio resistance is given by: A (X + LR1 + LR2 ) = B C Figure 4.2 Resistance Thermometer Bridge Circuit 53 Now when resistance X changes, the wheat-stone bridge becomes unbalance and thus galvanometer will give deflection which can be calibrated to give suitable temperature scale. Figure 4.3 The Basic Construction of Resistance Thermometer Resistance elements are generally long, spring like wires enclosed in a metal sheath. The construction of practical resistance thermometer is show figure 4.3.The resistance element is surrounded by a porcelain insulator which prevents short circuit between wire and metal sheath .Two leads are attached to each side of the platinum wire. When this instrument is placed in a liquid or a gas media whose temperature is to be measured, the sheath quickly reaches the temperature of the medium, this changes in temperature causes the platinum wire inside sheath to heat or cool, resulting in a proportional change in the wire’s resistance. This change in resistance can be directly calibrated to indicate the temperature. Figure 4.4 The Photograph of RTD Used in Experimental Setup 54 4.11.1.1Different Type of RTD Two wired: only used when high accuracy is not required as the resistance of the connecting wires is always included with that of the sensor leading to errors (figure 4.5). Figure 4.5 Two wire RTD Three wired: Using this method the two leads to the sensor are on adjoining arms, there is a lead resistance in each arm of the bridge and therefore the lead resistance is cancelled out (figure 4.5). Figure 4.5 Three wire RTD 55 Four-wired: It further increases the accuracy and reliability of the resistance being measured. In fig: 4.6 a standard two terminal RTD is used with another pair of wires to form an additional loop that cancels out the lead resistance. Figure 4.6 Three wire RTD Table 4.1 Comparison chart of various Resistance Temperature Detectors (RTD) Criteria Cost Platinum RTD 100 Ω wire wound and thin film Interchangeability Accuracy Repeatability Sensitivity(output) High Wide (-240 ºC to+ 649 ºC ) Excellent High Excellent Medium Response Medium Linearity Self heating Point(end)sensitive Lead effect Physical effect packaging Long term stability Good Very low Fair Medium Medium to small Good Temperature range Platinum RTD 1000 Ω thin film Nickel RTD 1000 Ω wire wound Balco RTD 2000 Ω wire wound Low Medium Medium Wide (-196 ºC to+ 538 ºC ) Medium (-212 ºC to+ 316 ºC) Short (-73ºC to+ 204 ºC ) Excellent High Excellent High Medium to Fast Good Medium Good Low Fair Medium Good High Fair Low Fair Very high Medium Medium Fair Medium Poor Low Fair Medium Poor Low Small to large Large Large Good Fair Fair 56 Advantages • They possess high accuracy of measurement. • They have a wide temperature range from -200 to 650ºC. • They are fast in response. • They have good reproducibility. • They have shown stable and accurate performance over many years. • Temperature compensation is not required. Disadvantages • Their cost is high. • They need a bridge circuit, power supply. • They show inaccuracy resulting from the current flowing through the bridge circuit and thereby heating the resistance element. • They have larger bulb size then thermocouple. 4.11.2 Thermocouples Industrial the most important temperature transducer is the thermocouple. The working principle of a thermocouple depends on the thermo-electric effect. If two dissimilar metals are joined together so as to form a closed circuit, there will be two junctions where they meet each other. If one of these is heated, then a current flow in the circuit which can be detected by galvanometer .The amount of the current produced depends on the difference in temperature between the two junctions and on the characteristics of the two metals. It was discovered by seebeek in 1821 that when two dissimilar metals are joined as shown in figure 4.7 with the two junction J1 and J2 at temperatures t1 and t2 respectively , than an emf arises, causing a current to flow in the circuit and this effect is known as Seebeck effect. Figure 4.7 The Basic Circuit of a Thermocouple 57 Seebeck effect is a bulk property and is expressed as E/q=αS T Where E is the Fermi energy and E/q=φ is the electrochemical potential α is the Seebeek coefficient which is dependent on material and temperature. Reference junction compensation a factor which is important in the use of thermocouple in the requirement of a known reference temperature of the reference junction. This is because when the reference junction is not at 0ºC, the observed value must be corrected by adding to it a voltage that has resulted a temperature difference equal to the amount by which the reference junction is above 0ºC. Now ET = Et +E0 Where E T is the total emf at temperature T, Et is the emf on account of temperature difference between detecting (hot) and the reference junction and E0 is the emf due to temperature of the reference junction being above 0ºC. Advantages • 2. They have inexpensive. • They are simple to use than resistance thermometer. • They have extremely wide temperature range from -270 ºC to 2800 ºC. • They have wide variety of designs both standard and special applications. • There electrical output is adaptable to variety of readout and /or control devices. • They have high response speed compared to filled systems thermometers. • They possess good accuracy and good reproducibility. • Calibration checking is easily made. Disadvantages • They have limited use in temperature spans of less than about 33ºC because of the relatively small change in junction voltages with temperature. • Extension leads must be house in metal conduit, as low junction voltage can cause the device to pickup stray electrical signals. • They need to hold reference junction temperatures constant or compensation for any deviations. • Their temperature –voltage relationship is non-linear. • They require much of an amplifier for many applications. 58 Table 4.2 Comparison chart of various Thermocouple Type Positive Wire Negative wire Min.Temp. (ºC) Max.Tem p.(ºC) Atmosphere environment Favorable point B Pt70 Rh30 Pt94-Rh6 0 1860 Inert or slow Oxidizing ---- E Chromel Constantan -196 999 Oxidizing Highest emf per ºC J Iron Constantan -196 760 Reducing Most economical K Chromel Alumel -190 1371 Oxidizing Most linear R Pt87Rh13 Platinum -18 1704 Oxidizing Small size, fast response S Pt90Rh10 Platinum -18 1760 Oxidizing Small size, fast response Good resist to corrosion from moisture T Copper Constantan -190 399 Oxidizing or Reducing Y Iron Constantan 129 982 Reducing ---- -- Tungste n W74-Re26 -18 2316 Inert High temperature W -Tungsten, Re - rhenium, Rh-rhodium, Ir- Iridium Figure 4.8 K-Type Thermocouple Figure 4.9 Bead of Thermocouple 59 4.11.3 Rotameters The rotameter is the most extensively used from of the variable area flow meter. It consists of a vertical tapered tube with a float which is free to move up or down within the tube, as shown in figure 4.10 .The tube is made tapered so that there is a linear relationship between the flow rate and position in the float within the tube. The free area between float and inside wall of the tube from an annular orifice. The tube is mounted vertically with the small end at the bottom. The fluid to be measured enters the tube from the bottom and passes upward around the float, and exit at the top. The tube materials of rotameter may be of glass or metal. The glass metering tubes are commonly used for relatively low pressure and temperature services of nonhazardous fluids such as water and air. Rotameters can directly measure flows as high as 4000 gps(920 leter/hr).Higher flow rates can be economically handled using the bypass –type rotameter which consists of an orifice plate located in the main line and sized to take a standard pressure drop at maximum flow. Figure 4.10 The Construction of Rotameter 60 Advantages • Its cost is relatively low. • It is good for metering small flows. • It handles wide variety of corrosives. • Viscosity-immune floats are available in rotameters. • It can be used in some light slurry services. • It has low pressure drop requirement. Disadvantages • The glass tube type is easily subject to breakage. • It must be mounted vertically. • Rotameters are limited to relatively low temperature. • The accuracy of rotameters is fair (about ±1/2 to ±10%). 4.11.4 Cup Anemometer Figure 4.11 Cup Type Anemometer Cup anemometers are widely used for a number of very good reasons. They are generally well suited to definition of mean wind speed (or more accurately wind run), they tend to be cost attractive in comparison to other types of instrument and they can be very robust. Measures the speed of a wind powered turbine in the form of 61 (usually hemispherical) cups mounted on radial spokes. Rotation speed can be measured by a number of different mechanisms, but often a magnet, affixed to the shaft, traversing past a fixed coil induces a pulse for each revolution, or a digital shaft encoder is used. Cup anemometers are not without their generic limitations, the principal ones being related to • ‘non-ideal’ sensitivity to angle of attacks out with the horizontal plane. • Dynamic response. • Non-linearity of calibration and variation in calibration caused by mechanical friction or due to the shape of the cups and, in some cases. • Changes in calibration sensitivity with horizontal wind direction. Advantages • Simple, omni directional (in one plane). Disadvantages • Moving parts wear out. • Slow to react to gusts. • Not sensitive to wind speeds of fractions of a meter per second. 4.11.5 Pump There are two main types of pumps- kinetic and positive displacement. Kinetic pumps are further divided into two categories of pumps- centrifugal and special effect (ex: jet pumps, hydraulic ram, etc.) in this set-up two centrifugal pumps have been used, one as a circulating pump and another as cold water feed pump. Table 4.3 Specification of Pump Used in Experiment Setup Sl.no Pump 1 Circulating pump 2 Feed water pump Rating Size: 25×25; H(DP): 13.5m; Q(DP): 1.2lps; Head range: 11.5-17.5; KW/HP: 0.37/ 0.5; 1 phase A.C.; 3.7 A. Size: 25×25; Head: 30 m; LPH: 2500max; KW:0.37; 240v, 1 phase, 50 Hz, AC; RPM: 2750; 2.2 A. Make Kirloskar Brothers Ltd Tullu 62 4.11.6 Pyranometer Figure 4.12 The Photograph of Pyranometer The pyranometer is used for the measurement of global or diffuse solar radiation over a hemispherical field of view. Basically it consists of a black surface, which heat up when exposed to the solar radiation. Its temperature increases until its rate of loss of heat by all causes is equal to the rate of gain of heat by radiation. This rise in temperature sets up a thermal e.m.f. which is measured on a mili voltmeter. The hot junctions of a thermopile are attached to the black surface, while the passive or cold junctions are located in such a way, that they do not receive any solar radiation. The hot junctions are arranged in the form of circular disc and are coated with a special black lacquer having very high absorptivity in the solar spectrum. The temperature difference between the hot and cold junctions is a function of the radiation falling on the sensitive surface. The sensitive disc surface is shielded by two concentric hemispherical optical glass domes having very good transmission characteristics, in order to protect that from weather and to reduce the tendency to form convective currents. It is essential to mount the pyranometer in the open, in such a position that there is no obstacle to obstruct the sun’s rays in all seasons between sunrise and sunset, and preferably no obstruction between the instrument and the sky down to the horizon in all directions Table 4.4 Specification of Pyranometer Used in Experiment Setup Sl.No 1 2 Position of Pyranometer Inclined at an angle of collector Inclined at an angle of collector Output constant (µVW -1m-2) Resistance (ohm) 16.66 116.36 7.72 11.86 Make Weather Technologies (I) Pvt. Ltd. National Instruments Ltd. 63 4.11.7 PC based On-Line Data Logger (HP 34970A) Figure 4.13 The Photograph of Multi-Channel of Data Logger The HP 34970A combines precision measurement capability with flexible signal connections for the production and development test systems. Three module slots are built into the rear of the instrument to accept any combination of data acquisition or switching modules. The combination of data logging and data acquisition features makes this instrument a versatile solution for the testing requirements now and in the future. 4.11.7.1 Convenient Data Logging Features (a) Direct measurement of thermocouples, RTDs, thermistors, dc voltage, ac voltage, resistance, dc current, ac current, frequency, and period. (b) Interval scanning with storage of up to 50,000 time-stamped readings. (c) Independent channel configuration with function, Mx+B scaling, and alarm limits available on a per-channel basis. (d) Intuitive user interface with knob for quick channel selection, menu navigation, and data entry from the front panel. (e) Portable, ruggedized case with non-skid feet. (f) HP BenchLink data Logger Software for Microsoft(R) Windows(R) included. 4.11.7.2 Flexible Data Acquisition/Switching Features • 61/2-digit multi meter accuracy, stability, and noise rejection. 64 • Up to 60 channels per instrument (120 single-ended channels). • Reading rates up to 600 readings pr second on a single channel and scan rates up to 250 channels per second. • Choice of multiplexing, matrix, general-purpose Form C switching, RF switching, digital I/O, totalize, and 16-bit analog output functions. • HP-IB (IEEE-488) interface and RS-232 interface are standard. • SCPI (Standard Commands for Programmable Instruments) compatibility. 4.11.7.3 HP Bench Link Data Logger Software at a Glance HP Bench Link Data Logger is a Windows-based application designed to make it easy to use the HP 34970A with the PC for gathering and analyzing measurements. This software is used to set up the test, acquire and archive measurement data, and performs real-time display and analysis of the incoming measurements. HP Benchlink Data Logger’s Key Functions Include the Following • Configure measurements o the spreadsheet-like Scan Setup page. • Display measurements graphically using the real-time Data Grid, Strip Chart, Readout, Bar Meter, XY Plot, and Histogram windows. • Add or configure graphics at any time. • Use graphical controls to set output voltages, close channels, output digital values, or view alarms. • Copy measurement data and graphics to a file or to the Clipboard for use in other applications. • Add textual annotation and explanations o measurement results and test reports. • Track readings on a single channel through the Monitor toolbar. • Enter information into the Event Log automatically or manually while acquiring measurement data or during post-scan analysis. • Print scans setups, event logs, and graphics. • Communicate with the instrument using HP-IB, RS-232, modem, or LAN (using a LAN-to-HP-IB gateway). 65 • In the present thesis work, the PC is connected with the data logger unit with the RS-232 interface, and the measurement data are stored in the memory of the PC directly. 4.11.8 Stevenson’s Screen Figure 4.14 The Photograph of Stevenson’s Screen Provision was made to record the outdoor ambient temperature variation using thermocouple sensors located within a Stevenson’s Screen. The thermocouple terminals were connected to the data logger. The scanning time was set to 1 minutes for data acquisition. 4.11.9 Constant temperature oil bath Figure 4.15 The Setup of Constant Temperature Oil Bath 66 The oil bath was used to calibrate the RTDs and thermocouple wires with respect to a standard PT100 RTD. Make: Concepts International Band: 100 Oil Used: Transformer Oil The calibration curves different RTD and Thermocouple used in the experiment against oil bath temperature are shown the flowing figure. The calibration constant also found from the equation of the plotted curves. Table 4.5 Calibration Equation Of RTDs and Thermocouples Sl. No. RTD and Thermocouple Name Calibration Equation 1 RTD - 09 Y = 0.9837732413 * X - 2.590396135 2 RTD - 10 Y = 0.9824238117 * X - 3.145484377 3 RTD - 11 Y = 1.014509994 * X - 8.381821036 4 RTD - 12 Y = 0.9952314984 * X - 2.814666106 5 Thermocauple-1(Thick) Y = 1.001660891 * X - 3.915486518 6 Thermocauple-2(Thin) Y = 1.011499462 * X - 3.984632047 67 RTD - 09 140 Oil BathTemperature(0C) 120 100 80 60 40 40 60 80 100 120 140 120 140 RTD Temperature(0C) Figure 4.16 Calibration Curve of RTD – 09 RTD - 10 140 Oil Bath Temperature(0C) 120 100 80 60 40 40 60 80 100 RTD Temperature( C) 0 Figure 4.17 Calibration Curve of RTD -10 68 RTD -11 140 Oil BathTemperature(0C) 120 100 80 60 40 40 60 80 100 120 140 120 140 RTD Temperature(0C) Figure 4.18 Calibration Curve of RTD -11 RTD - 12 140 Oil BathTemperature(0C) 120 100 80 60 40 40 60 80 100 RTD Temperature(0C) Figure 4.19 Calibration Curve of RTD -12 69 Thermocauple - 1 (Thick) 140 Oil BathTemperature(0C) 120 100 80 60 40 40 60 80 100 120 140 RTD Temperature(0C) Figure 4.20 Calibration Curve of Thermocauple-1(Thick) Thermocauple - 2 (Thin) 140 Oil BathTemperature(0C) 120 100 80 60 40 40 60 80 100 120 140 RTD Temperature(0C) Figure 4.21 Calibration Curve of Thermocauple-2 (Thin) 70 4.12 Developed Testing facility for two collector simultaneously Figure 4.22 Line Diagram for testing two collectors simultaneously Figure 4.23 The Photograph for testing two collectors simultaneously 71 4.13 Flow Chart Develop Coding For Automatically Evaluating System Efficiency & X in Different Scan Time Interval 72 Chapter 5 Results and Discussions 73 5.1 Calculation of Solar Noon 12-03-10 n(nth day of the year) 71 B=(n-1) X (360/365) 69.041 E(time correction factor) -10.463 Local Solar Noon 11:48:20.4 2 13-03-10 72 70.027 -10.195 11:48:04.2 3 23-03-10 82 79.890 -07.241 11:45:06.6 4 25-03-10 84 81.863 -06.611 11:44:28.8 5 30-03-10 89 86.794 -05.017 11:42:53.4 6 04-04-10 94 91.726 -03.436 11:41:18.6 7 05-04-10 95 93.698 -02.818 11:40:41.4 8 11-04-10 101 98.630 -01.336 11:39:12.6 9 12-04-10 102 99.616 -01.053 11:38:55.8 Sl. No. Date 1 5.2 Calculation of Mass Capacitance Mass of Water in Specific Heat of Tank (Kg) Water(J/Kg K) 12-03-10 92.50 4.1843X103 387.0478 2 13-03-10 92.50 4.1813 X103 386.7703 3 23-03-10 92.50 4.1842 X103 387.0385 4 25-03-10 92.50 4.1843 X103 387.0478 5 30-03-10 92.50 4.1848 X103 387.094 6 04-04-10 92.50 4.1916 X103 387.723 7 05-04-10 92.50 4.1899 X103 387.5658 8 11-04-10 92.50 4.1962 X103 388.1485 9 12-04-10 92.50 4.1964 X103 388.167 Sl. No. Date 1 (MC)s J/K 74 5.3 Gross Area of Collector Length(m) Breadth(m) Area(m2) 1.38 0.86 1.18 5.4 Day Time Test (W/m2) ∆T(K)=[(Tsid + Tsfd)/2]- Tad XC(m2K/W)= ∆T(K)/ GT ηsystem Wind speed (m/s) 34.83 622.80 23.99 0.038 0.37 1.55 67.29 37.23 707.83 18.18 0.025 0.44 1.39 69.88 34.05 653.59 24.70 0.037 0.45 0.92 67.5 31.13 677.13 24.83 0.036 0.45 0.59 Date Tsid (ºC) Tsfd (ºC) Tad GT (ºC) 12-03-10 50.06 67.59 13-03-10 43.53 23-03-10 47.63 25-03-10 44.42 30-03-10 63.46 82.52 31.97 726.05 41.02 0.056 0.35 0.89 04-04-10 62.39 80.51 32.9 666.98 38.55 0.057 0.36 1.44 05-04-10 66.34 82.6 33.46 606.52 41.01 0.067 0.35 0.50 11-04-10 71.34 91.92 35.76 729.50 45.87 0.062 0.36 0.50 12-04-10 74.75 94.45 33.66 714.92 50.94 0.071 0.36 0.79 5.5 Night time Test Date Tsin(ºC) Tsfn(ºC) Tan (ºC) t2-t1(Sec) Usn(W/m2K) 12-03-10 57.65 52.95 29.88 10 Х 3600 -1.7388 13-03-10 43.93 41.59 29.59 10 Х 3600 -1.6708 16-03-10 60.03 54.11 26.54 10 Х 3600 -1.8243 17-03-10 52.59 48.26 26.62 10 Х 3600 -1.7107 18-03-10 60.67 53.24 26.69 10 Х 3600 -2.1947 19-03-10 58.53 50.32 27.91 10 Х 3600 -2.9276 21-03-10 64.73 55.19 27.96 10 Х 3600 -2.8171 22-03-10 79.98 68.01 26.49 10 Х 3600 -2.3758 23-03-10 49.50 45.72 27.02 10 Х 3600 -2.0845 75 5.6 Day Time Test Curve Plot of test point along with a trend line drawn using regression method of least square curve fitting 0.80 Efficiency 0.60 0.40 0.20 0.00 0.00 0.02 0.04 0.06 0.08 X(m2K/W) Figure 5.1 Least Square Curve Fitting Variation of System Efficiency With X For different values of X, Efficiency are plotted in Figure 5.1.From the linear regression fitting of the plotted data the flowing equation is found Y = -2.270651943 * X + 0.5010580803 (5.1) From Equation, 5.1 at X=0, ηsys,0 =0.5010 Substituting ηsys,0 ηc in Equation 4.5, we get ηsystem 76 5.7 Day Time Heat Loss Calculation Date ηsystem ηsys,0 X Usys,d 12-03-10 0.37 0.5010 0.038 -3.447 13-03-10 0.44 0.5010 0.025 -2.440 23-03-10 0.45 0.5010 0.037 -1.378 25-03-10 0.45 0.5010 0.036 -1.417 30-03-10 0.35 0.5010 0.056 -2.696 04-04-10 0.36 0.5010 0.057 -2.474 05-04-10 0.35 0.5010 0.067 -2.254 11-04-10 0.36 0.5010 0.062 -2.274 12-04-10 0.36 0.5010 0.071 -1.986 5.8 Pressure Test Pressure(Kg/cm2) Initial 0 Time Duration(min) Water Temperature(ºC) 30 62.5 Final 0.2 Observation No Leakage observed. 5.9 System Efficiency at Standard Test Conditions Standard Test Conditions ( Ts =50ºC, Tad =25ºC, G T =700 W/m²): Standard Test Conditions Value of X 0.03571 ηsys, o Usys.0 0.5010 -2.2628 System Efficiency at Standard Test Conditions 0.420195 77 5.10 Thermal Energy Stored In the Storage Tank during Seven Hour of the Day Time Test Q= ηsystem(Corresponding to standard conditions) X Ac X 0.700 Date ηsystem Ac(m2) Q(kWh) 12-03-10 0.37 1.18 0.30562 13-03-10 0.44 1.18 0.36344 23-03-10 0.45 1.18 0.37170 25-03-10 0.45 1.18 0.37170 30-03-10 0.35 1.18 0.28910 04-04-10 0.36 1.18 0.29736 05-04-10 0.35 1.18 0.28910 11-04-10 0.36 1.18 0.29736 12-04-10 0.36 1.18 0.29736 78 1200 Date : 12-03-2010 Radiation(W/m2) One minute interval Two minute interval Five minute interval Ten minute interval 800 400 40 6 8 10 12 14 16 6 8 10 12 14 16 Temperature(0C) 38 36 34 32 30 28 Time(Hours) Figure 5.2 Variations of Solar Radiation and Ambient Temperature in Different Interval Scans Time 79 1200 Date : 13-03-2010 One minute interval Two minute interval Five minute interval Ten minute interval Radiation(W/m2) 1000 800 600 400 200 42 8 10 8 10 12 14 16 12 14 16 Temperature(0C) 40 38 36 34 32 30 Time(Hours) Figure 5.3 Variations of Solar Radiation and Ambient Temperature in Different Interval Scans Time 80 1200 Date : 23-03-2010 One minute interval Two minute interval Five minute interval Ten minute interval Radiation(W/m2) 1000 800 600 400 200 38 8 10 8 10 12 14 16 12 14 16 Temperature(0C) 36 34 32 30 28 26 Time(Hours) Figure 5.4 Variations of Solar Radiation and Ambient Temperature in Different Interval Scans Time 81 1200 Date : 25-03-2010 One minute interval Two minute interval Five minute interval Ten minute interval Radiation(W/m2) 1000 800 600 400 200 34 6 8 10 12 14 16 6 8 10 12 14 16 Temperature(0C) 32 30 28 26 Time(Hours) Figure 5.5 Variations of Solar Radiation and Ambient Temperature in Different Interval Scans Time 82 1200 Date : 30-03-2010 One minute interval Two minute interval Five minute interval Ten minute interval Radiation(W/m2) 1000 800 600 400 40 200 8 10 12 14 16 8 10 12 14 16 Temperature(0C) 38 36 34 32 30 28 Time(Hours) Figure 5.6 Variations of Solar Radiation and Ambient Temperature in Different Interval Scans Time 83 1200 Date : 04-04-2010 One minute interval Two minute interval Five minute interval Ten minute interval Radiation(W/m2) 1000 800 600 400 36 200 6 8 10 12 14 16 6 8 10 12 14 16 Temperature(0C) 34 32 30 28 Time(Hours) Figure 5.7 Variations of Solar Radiation and Ambient Temperature in Different Interval Scans Time 84 1200 Date : 05-04-2010 Radiation(W/m2) One minute interval Two minute interval Five minute interval Ten minute interval 800 400 38 6 8 10 12 14 16 6 8 10 12 14 16 Temperature(0C) 36 34 32 30 28 Time(Hours) Figure 5.8 Variations of Solar Radiation and Ambient Temperature in Different Interval Scans Time 85 1200 Date : 11-04-2010 Radiation(W/m2) One minute interval Two minute interval Five minute interval Ten minute interval 800 400 40 6 8 10 12 14 16 6 8 10 12 14 16 Temperature(0C) 38 36 34 32 30 28 Time(Hours) Figure 5.9 Variations of Solar Radiation and Ambient Temperature in Different Interval Scans Time 86 1200 Date : 12-04-2010 One minute interval Two minute interval Five minute interval Ten minute interval Radiation(W/m2) 1000 800 600 400 200 36 6 8 10 12 14 16 6 8 10 12 14 16 Temperature(0C) 34 32 30 28 Time(Hours) Figure 5.10 Variations of Solar Radiation and Ambient Temperature in Different Interval Scans Time 87 5.11 Impact of Time Constant on Performance Efficiency 1 min Date interval 2 min interval 5 min interval 10 min interval Efficiency 0.3734730 0.3750290 0.3776890 Deviation 0.0002220 0.0017780 0.0044380 % of Deviation 0.0594770 0.4763550 1.1890122 Efficiency 0.4534650 0.4545490 0.4569630 Deviation 0.0000520 0.0011360 0.0035500 % of Deviation 0.0114685 0.2505440 0.7829506 Efficiency 0.4615600 0.4619600 0.4643750 Deviation 0.0005380 0.0009380 0.0033530 % of Deviation 0.1166972 0.2034610 0.7272971 Efficiency 0.4596530 0.4596000 0.4612650 Deviation 0.0004970 0.0004440 0.0021090 % of Deviation 0.1082420 0.0966991 0.4593210 Efficiency 0.3547220 0.3549640 0.3564320 Deviation 0.0000860 0.0003280 0.0017960 % of Deviation 0.0242502 0.0924892 0.5064347 Efficiency 0.3664600 0.3673810 0.3689840 Deviation - 0.000340 0.0005810 0.0021840 % of Deviation - 0.092693 0.1583969 0.5954198 Efficiency 0.3601180 0.3617120 0.3664433 Deviation 0.0001410 0.0017350 0.0064663 % of Deviation 0.0391691 0.4819752 1.7963092 Efficiency 0.3593350 0.360448 0.362365 Deviation 0.0000910 0.000904 0.002821 % of Deviation 0.2514295 0.784604 Efficiency 0.0253310 0.3694770 0.3703370 0.371838 Deviation - 0.0003170 0.0005430 0.002044 % of Deviation - 0.0857230 0.1468385 0.552740 Efficiency 12-03-10 13-03-10 23-03-10 25-03-10 30-03-10 04-04-10 05-04-10 11-04-10 12-04-10 0.373251 0.4534130 0.4610220 0.4591560 0.3546360 0.3668000 0.3599770 0.3592440 0.3697940 88 5.12 Recommendation of Tank Volume Measurement Domestic solar hot water system Make - EXIDE INDUSTRIES LIMITED Model- ETC 100LPD All the calculation are made with reference to working volume of the hot water tank Sl. no. Volume in (Lt) Various Temperature Corrected volume (Lt) in 20ºC Volume(Lt) converted into Weight(Kg) Actual tank volume in (Kg) % of Error in volume measurement 1 82.40 82.64048 82.49421 81.687 0.988175 2 82.45 82.78591 82.63938 82.008 0.769897 It is found the measurement of tank volume by measuring weight of the water is more accurate compare to the measurement of volume directly. 89 Chapter 6 Conclusion and Scope of Future Work 90 6.1 Conclusion • From the experimental study it is found that the direct measurement of tank volume with the help of measuring cylinder is more tedious and erroneous compared to indirect measurement of tank volume i.e. by measuring weight of the water inside the tank and then converting it into volume. The possible reason of this error is due to the parallax error of the series of measurement. It is found that the measurement of volume directly by measuring cylinder, the error in measurement may reach to around 1%. • It is observed that the efficiency of the system gradually increases with the increase in scan time interval. The possible reason of the better performance is due to the fact that the integration average of the solar radiation over the longer scan interval will make the radiation profile less fluctuating. 6.2 The Future Scopes of Work Are As Follows • The effect of varying tank size on the efficiency of the system can be evaluated. It is possible to find an optimum size of tank volume where the best efficiency will be achieved. • The system performance may be evaluated with constant tank volume with varying collector aperture Area. • Optimization sizing of solar water heating system. 91 References 1. A. El Fadar, A. Mimet, A. Azzabakh, M. Perez-Garcia, J. Castaing. Applied Thermal Engineering 29 (2009) 1267–1270. 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