Solar energy applications could be the best alternative to the conventional fuels for the purposes of domestic,water and space heating and some industries in the sunny,arid,and hot areas.In the present study,the perfo...Solar energy applications could be the best alternative to the conventional fuels for the purposes of domestic,water and space heating and some industries in the sunny,arid,and hot areas.In the present study,the performance of an evacuated tube solar heater for water heating for months of February and March was experimentally investigated.This was performed in a hot and arid area(Nasiriya City,South of Iraq).A solar heater with ten evacuated tube solar collectors with a capacity of 100 liter was used in the experiments.Each evacuated tube had a length of 1.8m with an outside diameter of 8 cm.It was observed that for the two selected months,water temperature of the solar heater reached a maximum more than 70°C during sunny days with no heat extraction from the tank of the solar heater.Moreover,heat was extracted from the solar collector with four different flowrates 0.5,0.75,1,and 1.25 l/min,respectively.The results showed that temperature of the solar heater behaved differently from the static situation.When the heat extraction begun,there was a gradual and noticeable decrease in the water temperature of the heater.The observed decrease was slight with the lowest flowrate(0.25 l/m)and becomes sharp with the highest flowrate(1.25 l/min).However,water temperature of the solar heater remained higher than 40°C for the investigated flowrates except the case of 1.25 l/min.The results showed that evacuated tube solar heater can work efficiently in arid and hot areas in winter and spring seasons when the conditions of solar radiation are suitable.展开更多
Solar water heaters which provide a cost-effective and environmental friendly approach to hot water generation are in widespread application. Evacuated tube solar water heaters perform better than flat plate solar wat...Solar water heaters which provide a cost-effective and environmental friendly approach to hot water generation are in widespread application. Evacuated tube solar water heaters perform better than flat plate solar water heaters as a result of their greater surface area exposed for sunlight absorption. Water-in-glass evacuated tube solar water heaters are widely used as compared to heat-pipe solar water heaters due to their short payback periods. In this study, the performance of water-in-glass evacuated tube solar water heater is investigated through experiments under the climatic conditions in Kenya. The results revealed a daily efficiency range of 0.58 - 0.65 and a daily final outlet temperature greater than 55<span style="white-space:normal;">°</span>C given an initial temperature of 25°C.展开更多
Solar water collectors that uses for domestic and industrial applications within temperature up to, are classified under two main types: Flat Plate collector (FP), and Evacuated Tube collector (ET). Thermal performanc...Solar water collectors that uses for domestic and industrial applications within temperature up to, are classified under two main types: Flat Plate collector (FP), and Evacuated Tube collector (ET). Thermal performance test results showed that each type have different thermal features. Comparison between (FP & ET) collectors showed that they could take advantages of different thermal features of two types when they work in the same climatic conditions and overlap of these thermal features when they work in different operational conditions. They can take advantage of these features through (compound) solar collector. Compound solar water Collector (CO) composed of a part of flat plate collector shape (FP), and a part of evacuated tube collector shape (ET). Booth have equal reference area, and connected together to be as one Solar collector (CO). Water entered first flat part (FP), then evacuated tube part (ET) then to tank or end-use. In this paper, present design and manufacturing as well the thermal performance test of (compound) solar collector, according to Standard Specification of tests, was EN12975:2001. Mechanical test for (CO) collector conducted successfully according to durability, reliability, and safety requirements. In addition, thermal performance was tested in steady state at the climatic conditions of Damascus city, and concluded the thermal performance of (FP & ET) that constitute (CO) collector. The results showed enhancement of thermal performance.展开更多
A hybrid solar collector was designed to investigate the effects of combining two different solar collector techniques on the overall collector’s effectiveness. While most solar collectors focus only on one solar col...A hybrid solar collector was designed to investigate the effects of combining two different solar collector techniques on the overall collector’s effectiveness. While most solar collectors focus only on one solar collection method, the small hybrid system uses a flat plate collector in conjunction with five evacuated tubes to absorb the most energy possible from both direct and diffuse solar radiation. Data was collected over four months while the system operated at different flow rates and with various levels of available insolation from the sun to evaluate the performance of the solar collector. To understand the relative contribution of the flat plate collector and the evacuated tubes, temperature differences across each part of the system were measured. The results indicate the average first law efficiency of the hybrid system is 43.3%, significantly higher than the performance of the flat plate alone. An exergy analysis was performed for this system to assess the performance of the flat plate system by itself. Results of the second law analysis were comparable to the exergetic efficiencies of other experimental collectors, around 4%. Though the efficiencies were in the expected range, they reveal that further improvements to the system are possible.展开更多
China has abundant solar energy resource. Solar thermal collectors, particularly all-glass evacuated tubular collectors, have been studied and developed for 30 years, and solar thermal industry has developed rapidly f...China has abundant solar energy resource. Solar thermal collectors, particularly all-glass evacuated tubular collectors, have been studied and developed for 30 years, and solar thermal industry has developed rapidly for 15 years. There are various solar thermal systems, with an operation area of around 108 million m2 in 2007. These systems mainly provide domestic hot water, but some other applications are under extensive study and development as well.展开更多
Using combined cooling,heat and power systems can be an appropriate substitute for preventing emissions of pollutants and excessive consumption of fossil fuels.Utilizing renewable energy in these systems as a source o...Using combined cooling,heat and power systems can be an appropriate substitute for preventing emissions of pollutants and excessive consumption of fossil fuels.Utilizing renewable energy in these systems as a source of power generation can be an appropriate substitute for fossil-fuel-based systems.Therefore,in this paper,cogeneration cooling,heat and power systems based on gas-fired internal combustion engines with a solar-thermal system with evacuated tube collectors have been modelled and thermo-economic analysis has been done to compare fossil-fuel-based systems.The required rate of heat to supply the hot water is 50 kW.In the studied system,the internal combustion engine produces electrical energy.Then,the solar-thermal system with evacuated tube collectors and the gas-burning generator provide the thermal energy required by the studied building and the primary stimulus of the absorption chiller for cooling.In this study,two different scenarios are conducted in states considering simultaneous production systems and regardless of this environmental and thermo-economic analysis system.The results showed that the efficiency of the studied system was 60% in summer and 56% in winter.展开更多
This paper introduces a novel flat plate solar collector(FPC) using micro heat pipe array(MHPA) as a key element.To analyze the thermal transfer behavior of flat plate solar collector with micro heat pipe array(MHPA-F...This paper introduces a novel flat plate solar collector(FPC) using micro heat pipe array(MHPA) as a key element.To analyze the thermal transfer behavior of flat plate solar collector with micro heat pipe array(MHPA-FPC),an indoor experiment for thermal transfer characteristic of MHPA applied to FPC was conducted by using an electrical heating film to simulate the solar radiation.Different cooling water flow rates,cooling water temperatures,slopes,and contact thermal resistances between the condenser of MHPA and the heat exchanger were tested at different heating powers.The experimental results indicate that MHPA-FPC exhibits the enhanced heat transfer capability with increased cooling water flow rate and temperature.Total thermal resistance has a maximum decline of approximately 10% when the flow rate increases from 180 to 360 L h 1 and 38% when the cooling water temperature increases from 20℃ to 40℃.When the inclination angle of MHPA-FPC exceeds 30°,the slope change has a negligible effect on the heat transfer performance of MHPA-FPC.In addition,contact thermal resistance significantly affects the heat transfer capability of MHPA-FPC.The total thermal resistances lowers to nearly half of the original level when contact material between the condenser of MHPA and the heat exchanger changes from conductive silicone to conductive grease.These results could provide useful information for the optimal design and operation of MHPA-FPC.展开更多
The experimental system of heat loss of all-glass evacuated solar collector tubes(evacuated tube) is firstly designed and constructed,which uses electric heater as thermal resource.The equilibrium temperatures are les...The experimental system of heat loss of all-glass evacuated solar collector tubes(evacuated tube) is firstly designed and constructed,which uses electric heater as thermal resource.The equilibrium temperatures are less than±1℃during the test.and the temperature differences of up/middle/low node in the tube are less than 1℃,3℃,and 7℃respectively.The heat loss of evacuated tube increases about 2.7%with vacuum state of 0.01--1 mPa,and it has the best performance at tube temperature of 20--280℃.The invalidation tube(>200 mPa) has the biggest heat loss that increases linearly with the tube temperature.The evacuated tubes with the vacuum of 0.01-1 mPa are suitable for most solar adsorption refrigeration.展开更多
As a new type of equipment for solar medium temperature utilization, the compound parabolic concentrator-pulsating heat pipe solar collector(CPC-PHPSC) uses pulsating heat pipe(PHP) as an endotherm, which can realize ...As a new type of equipment for solar medium temperature utilization, the compound parabolic concentrator-pulsating heat pipe solar collector(CPC-PHPSC) uses pulsating heat pipe(PHP) as an endotherm, which can realize efficient energy conversion. The design of proper concentration ratio of compound parabolic concentrator(CPC) ensures that the incident sunlight can be concentrated on the evaporator section surface of PHP without solar tracking system. The objective of the present work is to study the influence of solar radiation intensity, air speed, material thickness(glass and insulation board) and tilt angle on the thermal performance of the new collector, which is difficult to control in the experiment. The heat leakage process and characteristics of the CPC-PHPSC were numerically studied by establishing a 3D numerical model of the collector unit. The results show that the theoretical collector efficiency of CPC-PHPSC reaches 74.5%, which is consistent with the experimental results. During operation, the heat collection performance is the best when the tilt angle is 45° and the solar radiation intensity is 1000 W/m^(2), while the excessive air speed will increase the convective heat loss. Increasing the thickness of insulation board and glass has little effect on the collector efficiency.展开更多
Heat transfer in the evacuated collector tube is a three-dimensional laminar natural convection prob-lem driven by buoyancy. Because of its complexity, no effective theoretical model is available despiteof limited exp...Heat transfer in the evacuated collector tube is a three-dimensional laminar natural convection prob-lem driven by buoyancy. Because of its complexity, no effective theoretical model is available despiteof limited experimental work which is confined to one aspect- The present work aims to depict theconvective heat transfer inside a tweended inclined tube with East-West symmetric heat input us-ing numerical methods. Based on reasonable assumptions, governing equations of the inside fluid areestabllshed. The corresponding discretizated equations are solved by employing numerical methods.The calculated results are displayed for velocity and temperature profiles on different cross-sectionalplanes, which present the flow pattern characterized by upflow and dowallow along the axial direc-tion and adherent flow along the peripheral direction, and the heat transfer process from the wall tothe center. Furthermore, the transient Nusselt number and average temperature level are shown anddiscussed. Finally, the parametric effects of the tube radius and the heat input on the flow and heattransfer are also given.展开更多
Commercial building sector accounts for 8% of the total electricity consumption in India. Cooling activities (HVAC) in commercial buildings consume 55% of the total energy utilized. Consequently, CO<sub>2</su...Commercial building sector accounts for 8% of the total electricity consumption in India. Cooling activities (HVAC) in commercial buildings consume 55% of the total energy utilized. Consequently, CO<sub>2</sub> emissions from conventional buildings in India were estimated to be 98 metric tonnes of CO<sub>2</sub> per million ft<sup>2</sup> in 2014. Solar thermal air conditioning can be the solution to these demands and can contribute to about 15% to 20% of India’s total oil consumption thereby reducing the dependence on fossil fuels. Hence, the main objective of the work is to model and simulate a solar absorption cooling system for GERMI office building located in Gandhinagar, Gujarat, India, using the transient simulation software ‘TRNSYS’. Cooling load estimation and comfort conditions required for the building were determined based on ASHRAE standards. Evacuated tube collectors were selected because of its market availability, ease of manufacturing and proven technology. Single effect absorption chiller was used because of its commercial availability. The effects of storage tank volume, collector area and collector slope were also investigated for parametric optimization. The results of the simulation and parametric analysis are analyzed and presented in the paper.展开更多
文摘Solar energy applications could be the best alternative to the conventional fuels for the purposes of domestic,water and space heating and some industries in the sunny,arid,and hot areas.In the present study,the performance of an evacuated tube solar heater for water heating for months of February and March was experimentally investigated.This was performed in a hot and arid area(Nasiriya City,South of Iraq).A solar heater with ten evacuated tube solar collectors with a capacity of 100 liter was used in the experiments.Each evacuated tube had a length of 1.8m with an outside diameter of 8 cm.It was observed that for the two selected months,water temperature of the solar heater reached a maximum more than 70°C during sunny days with no heat extraction from the tank of the solar heater.Moreover,heat was extracted from the solar collector with four different flowrates 0.5,0.75,1,and 1.25 l/min,respectively.The results showed that temperature of the solar heater behaved differently from the static situation.When the heat extraction begun,there was a gradual and noticeable decrease in the water temperature of the heater.The observed decrease was slight with the lowest flowrate(0.25 l/m)and becomes sharp with the highest flowrate(1.25 l/min).However,water temperature of the solar heater remained higher than 40°C for the investigated flowrates except the case of 1.25 l/min.The results showed that evacuated tube solar heater can work efficiently in arid and hot areas in winter and spring seasons when the conditions of solar radiation are suitable.
文摘Solar water heaters which provide a cost-effective and environmental friendly approach to hot water generation are in widespread application. Evacuated tube solar water heaters perform better than flat plate solar water heaters as a result of their greater surface area exposed for sunlight absorption. Water-in-glass evacuated tube solar water heaters are widely used as compared to heat-pipe solar water heaters due to their short payback periods. In this study, the performance of water-in-glass evacuated tube solar water heater is investigated through experiments under the climatic conditions in Kenya. The results revealed a daily efficiency range of 0.58 - 0.65 and a daily final outlet temperature greater than 55<span style="white-space:normal;">°</span>C given an initial temperature of 25°C.
文摘Solar water collectors that uses for domestic and industrial applications within temperature up to, are classified under two main types: Flat Plate collector (FP), and Evacuated Tube collector (ET). Thermal performance test results showed that each type have different thermal features. Comparison between (FP & ET) collectors showed that they could take advantages of different thermal features of two types when they work in the same climatic conditions and overlap of these thermal features when they work in different operational conditions. They can take advantage of these features through (compound) solar collector. Compound solar water Collector (CO) composed of a part of flat plate collector shape (FP), and a part of evacuated tube collector shape (ET). Booth have equal reference area, and connected together to be as one Solar collector (CO). Water entered first flat part (FP), then evacuated tube part (ET) then to tank or end-use. In this paper, present design and manufacturing as well the thermal performance test of (compound) solar collector, according to Standard Specification of tests, was EN12975:2001. Mechanical test for (CO) collector conducted successfully according to durability, reliability, and safety requirements. In addition, thermal performance was tested in steady state at the climatic conditions of Damascus city, and concluded the thermal performance of (FP & ET) that constitute (CO) collector. The results showed enhancement of thermal performance.
文摘A hybrid solar collector was designed to investigate the effects of combining two different solar collector techniques on the overall collector’s effectiveness. While most solar collectors focus only on one solar collection method, the small hybrid system uses a flat plate collector in conjunction with five evacuated tubes to absorb the most energy possible from both direct and diffuse solar radiation. Data was collected over four months while the system operated at different flow rates and with various levels of available insolation from the sun to evaluate the performance of the solar collector. To understand the relative contribution of the flat plate collector and the evacuated tubes, temperature differences across each part of the system were measured. The results indicate the average first law efficiency of the hybrid system is 43.3%, significantly higher than the performance of the flat plate alone. An exergy analysis was performed for this system to assess the performance of the flat plate system by itself. Results of the second law analysis were comparable to the exergetic efficiencies of other experimental collectors, around 4%. Though the efficiencies were in the expected range, they reveal that further improvements to the system are possible.
文摘China has abundant solar energy resource. Solar thermal collectors, particularly all-glass evacuated tubular collectors, have been studied and developed for 30 years, and solar thermal industry has developed rapidly for 15 years. There are various solar thermal systems, with an operation area of around 108 million m2 in 2007. These systems mainly provide domestic hot water, but some other applications are under extensive study and development as well.
文摘Using combined cooling,heat and power systems can be an appropriate substitute for preventing emissions of pollutants and excessive consumption of fossil fuels.Utilizing renewable energy in these systems as a source of power generation can be an appropriate substitute for fossil-fuel-based systems.Therefore,in this paper,cogeneration cooling,heat and power systems based on gas-fired internal combustion engines with a solar-thermal system with evacuated tube collectors have been modelled and thermo-economic analysis has been done to compare fossil-fuel-based systems.The required rate of heat to supply the hot water is 50 kW.In the studied system,the internal combustion engine produces electrical energy.Then,the solar-thermal system with evacuated tube collectors and the gas-burning generator provide the thermal energy required by the studied building and the primary stimulus of the absorption chiller for cooling.In this study,two different scenarios are conducted in states considering simultaneous production systems and regardless of this environmental and thermo-economic analysis system.The results showed that the efficiency of the studied system was 60% in summer and 56% in winter.
基金financially supported by the Natural Science Foundation of Beijing(Grant No.Z1004020201201)the Opening Funds of State Key Laboratory of Building Safety and Build Environment of China(Grant No.BSBE 2011-07)
文摘This paper introduces a novel flat plate solar collector(FPC) using micro heat pipe array(MHPA) as a key element.To analyze the thermal transfer behavior of flat plate solar collector with micro heat pipe array(MHPA-FPC),an indoor experiment for thermal transfer characteristic of MHPA applied to FPC was conducted by using an electrical heating film to simulate the solar radiation.Different cooling water flow rates,cooling water temperatures,slopes,and contact thermal resistances between the condenser of MHPA and the heat exchanger were tested at different heating powers.The experimental results indicate that MHPA-FPC exhibits the enhanced heat transfer capability with increased cooling water flow rate and temperature.Total thermal resistance has a maximum decline of approximately 10% when the flow rate increases from 180 to 360 L h 1 and 38% when the cooling water temperature increases from 20℃ to 40℃.When the inclination angle of MHPA-FPC exceeds 30°,the slope change has a negligible effect on the heat transfer performance of MHPA-FPC.In addition,contact thermal resistance significantly affects the heat transfer capability of MHPA-FPC.The total thermal resistances lowers to nearly half of the original level when contact material between the condenser of MHPA and the heat exchanger changes from conductive silicone to conductive grease.These results could provide useful information for the optimal design and operation of MHPA-FPC.
基金the National Natural Science Foundation of China(No.30771245)the Innovation Program of Shanghai Municipal Education Commission(No.09YZ229)the Leading Academic Discipline Project of Shanghai Municipal Education Commission(No.J50502)
文摘The experimental system of heat loss of all-glass evacuated solar collector tubes(evacuated tube) is firstly designed and constructed,which uses electric heater as thermal resource.The equilibrium temperatures are less than±1℃during the test.and the temperature differences of up/middle/low node in the tube are less than 1℃,3℃,and 7℃respectively.The heat loss of evacuated tube increases about 2.7%with vacuum state of 0.01--1 mPa,and it has the best performance at tube temperature of 20--280℃.The invalidation tube(>200 mPa) has the biggest heat loss that increases linearly with the tube temperature.The evacuated tubes with the vacuum of 0.01-1 mPa are suitable for most solar adsorption refrigeration.
基金supported by the National Natural Science Foundation of China (51506004)Beijing Municipal Natural Science Foundation (3162009)Beijing Youth Top-notch Talent Support Program (CIT&TCD201704057)。
文摘As a new type of equipment for solar medium temperature utilization, the compound parabolic concentrator-pulsating heat pipe solar collector(CPC-PHPSC) uses pulsating heat pipe(PHP) as an endotherm, which can realize efficient energy conversion. The design of proper concentration ratio of compound parabolic concentrator(CPC) ensures that the incident sunlight can be concentrated on the evaporator section surface of PHP without solar tracking system. The objective of the present work is to study the influence of solar radiation intensity, air speed, material thickness(glass and insulation board) and tilt angle on the thermal performance of the new collector, which is difficult to control in the experiment. The heat leakage process and characteristics of the CPC-PHPSC were numerically studied by establishing a 3D numerical model of the collector unit. The results show that the theoretical collector efficiency of CPC-PHPSC reaches 74.5%, which is consistent with the experimental results. During operation, the heat collection performance is the best when the tilt angle is 45° and the solar radiation intensity is 1000 W/m^(2), while the excessive air speed will increase the convective heat loss. Increasing the thickness of insulation board and glass has little effect on the collector efficiency.
文摘Heat transfer in the evacuated collector tube is a three-dimensional laminar natural convection prob-lem driven by buoyancy. Because of its complexity, no effective theoretical model is available despiteof limited experimental work which is confined to one aspect- The present work aims to depict theconvective heat transfer inside a tweended inclined tube with East-West symmetric heat input us-ing numerical methods. Based on reasonable assumptions, governing equations of the inside fluid areestabllshed. The corresponding discretizated equations are solved by employing numerical methods.The calculated results are displayed for velocity and temperature profiles on different cross-sectionalplanes, which present the flow pattern characterized by upflow and dowallow along the axial direc-tion and adherent flow along the peripheral direction, and the heat transfer process from the wall tothe center. Furthermore, the transient Nusselt number and average temperature level are shown anddiscussed. Finally, the parametric effects of the tube radius and the heat input on the flow and heattransfer are also given.
文摘Commercial building sector accounts for 8% of the total electricity consumption in India. Cooling activities (HVAC) in commercial buildings consume 55% of the total energy utilized. Consequently, CO<sub>2</sub> emissions from conventional buildings in India were estimated to be 98 metric tonnes of CO<sub>2</sub> per million ft<sup>2</sup> in 2014. Solar thermal air conditioning can be the solution to these demands and can contribute to about 15% to 20% of India’s total oil consumption thereby reducing the dependence on fossil fuels. Hence, the main objective of the work is to model and simulate a solar absorption cooling system for GERMI office building located in Gandhinagar, Gujarat, India, using the transient simulation software ‘TRNSYS’. Cooling load estimation and comfort conditions required for the building were determined based on ASHRAE standards. Evacuated tube collectors were selected because of its market availability, ease of manufacturing and proven technology. Single effect absorption chiller was used because of its commercial availability. The effects of storage tank volume, collector area and collector slope were also investigated for parametric optimization. The results of the simulation and parametric analysis are analyzed and presented in the paper.