The experimental study of natural convection in allglass evacuated tube solar collectors is performed through the experimental platform of the solar-assisted fuel cell system.The experimental facility includes solar c...The experimental study of natural convection in allglass evacuated tube solar collectors is performed through the experimental platform of the solar-assisted fuel cell system.The experimental facility includes solar collectors with different length and diameter tubes, different coating materials, and with / without guide plates, respectively. Threedimensional mathematical models on natural and forced convections in the solar collectors are established and the experimental data is validated by field synergy and entransy principles. The results of natural convection show that the water temperature increases and thermal efficiency decreases gradually with the evacuated tube length. The thermal efficiency increases when absorption rates increase from 0. 95 to 1. 0 and emission rates decrease from 0. 16 to 0. 06. The thermal efficiency of solar collectors is increased after being equipped with the guide plate, which is attributed to the disappearance of the mixed flowand the enhancement of the heat transfer at the bottom of the evacuated tube. The results of forced convertion indicate that the Reynolds, Nusselt and entransy increments of the horizontal double collectors are higher than those of the vertical single collector while the entransy dissipation is lower than that of the vertical single collector. It is concluded that the solar collectors with guide plates are suitable for natural convection while the double horizontal collectors are suitable for forced convection in the thermal field of solar-assisted fuel cell systems with lowand medium temperatures.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
System performance of solar water heaters depends upon collector and storage tank designs, solar radiation intensity and ambient temperature, amongst others. Evacuated glass tube collectors with U-tubes inside are les...System performance of solar water heaters depends upon collector and storage tank designs, solar radiation intensity and ambient temperature, amongst others. Evacuated glass tube collectors with U-tubes inside are less prone to leakages than the all-glass or the heat pipe types. U-tube solar water heaters suspended on walls and balconies could help overcome present day roof space restriction and increasing apartment-style housing. As such, their performance would depend upon its orientation when mounted in a vertical position. This paper reports the results of outdoor tests conducted on natural convection U-tube solar water heaters oriented towards different directions. Long and short term test procedures were employed to allow us to compare their performances as if they were tested simultaneously side-by-side.展开更多
New alternatives and inventive renewable energy techniques which encompass both generation and power management solutions are fundamental for meeting remote residential energy supply and demand today, especially if th...New alternatives and inventive renewable energy techniques which encompass both generation and power management solutions are fundamental for meeting remote residential energy supply and demand today, especially if the grid is quasi-inexistent. Solar thermoelectric generators mounted on a dual-axis sun tracker can be a cost-effective alternative to photovoltaics for remote residential household power generation. A complete solar thermoelectric energy harvesting system is presented in this paper for energy delivery to remote residential areas in developing regions. To this end, the entire system was built, modeled, and then validated with the LTspice simulator software via the thermal-to-electrical analogy schemes. Valuable data in conjunction with a novel LTspice circuit were obtained, showing the achievability of analyzing transient heat transfer with the SPICE simulator; however a few of the problems to be solved remain at the practical level. Despite the unusual operation of the thermoelectric modules with the solar radiation, the simulation and measurements were in good agreement, thus validating the new modeling strategy.展开更多
The MPPT （maximum power point tracking） is one of the most important features of a regulator system that processes the energy produced by a photovoltaic generator. It is necessary, in fact, to design a controller th...The MPPT （maximum power point tracking） is one of the most important features of a regulator system that processes the energy produced by a photovoltaic generator. It is necessary, in fact, to design a controller that is able to set the output value of the voltage and ensure the working within the maximum power point. In this paper, we propose the application of the robust sliding mode control technique to a DC-DC buck converter which is combined with a classical P ＆ O （perturbation and observation） algorithm to enhance the solar system efficiency. Dynamic equations describing the boost converter are derived and a sliding mode controller for a buck converter is designed. It is shown that, this control approach gives good results in terms of robustness toward load and input voltage variations. The effectiveness of the proposed work is verified by the simulation results under PowerSim environment.展开更多
Solar thermal propulsion system includes solar thermal propulsion and nuclear thermal propulsion, and it is a significant issue to improve the heat transfer efficiency of the solar thermal thruster. This paper propose...Solar thermal propulsion system includes solar thermal propulsion and nuclear thermal propulsion, and it is a significant issue to improve the heat transfer efficiency of the solar thermal thruster. This paper proposes a platelet configuration to be used in the heat exchanger core, which is the most important component of solar thermal system. The platelet passage can enhance the heat transfer between the propellant and the hot core heated by the concentrated sunlight. Based on fluid-solid coupled heat transfer, the paper utilized the platelet heat transfer characteristic to simulate the heat transfer and flow field of the platelet passage. A coupled system includes the coupled flow and heat transfer between the fluid region and solid region. The simulation result shows that the propellant can be heated to the design temperature of 2300K in platelet passage of the thermal propulsion system, and the fluid-solid coupled method can solve the heat transfer in the platelet structure more precisely.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
In the solar atmosphere, there exist two frequently-observed phenomena, Moreton waves and EIT(extreme-ultraviolet imaging telescope) waves, whose physical nature is still under debate. In this work, we perform a three...In the solar atmosphere, there exist two frequently-observed phenomena, Moreton waves and EIT(extreme-ultraviolet imaging telescope) waves, whose physical nature is still under debate. In this work, we perform a three-dimensional ray-tracing simulation for the propagation of fast magnetoacoustic waves. We build a stratified solar atmosphere model and take partial ionization into consideration to give an exact description of chromosphere and transition region. The calculated result is compared with a flare event observation in which both Moreton waves and EIT waves were present. In agreement with observations, the calculated wavefront show different kinematical characteristics in different propagation directions during different times.Moreton waves and EIT waves have higher propagation speeds near the active region where the magnetic field strength is strong. The result suggests that both Moreton waves and EIT waves of this event can be interpreted as the fast magnetoacoustic waves propagating at different heights in the solar atmosphere.展开更多
基金The National Natural Science Foundation of China(No.51376110,51541604)the Major International(Regional) Joint Research Project of the National Natural Science Foundation of China(No.61320106011)
文摘The experimental study of natural convection in allglass evacuated tube solar collectors is performed through the experimental platform of the solar-assisted fuel cell system.The experimental facility includes solar collectors with different length and diameter tubes, different coating materials, and with / without guide plates, respectively. Threedimensional mathematical models on natural and forced convections in the solar collectors are established and the experimental data is validated by field synergy and entransy principles. The results of natural convection show that the water temperature increases and thermal efficiency decreases gradually with the evacuated tube length. The thermal efficiency increases when absorption rates increase from 0. 95 to 1. 0 and emission rates decrease from 0. 16 to 0. 06. The thermal efficiency of solar collectors is increased after being equipped with the guide plate, which is attributed to the disappearance of the mixed flowand the enhancement of the heat transfer at the bottom of the evacuated tube. The results of forced convertion indicate that the Reynolds, Nusselt and entransy increments of the horizontal double collectors are higher than those of the vertical single collector while the entransy dissipation is lower than that of the vertical single collector. It is concluded that the solar collectors with guide plates are suitable for natural convection while the double horizontal collectors are suitable for forced convection in the thermal field of solar-assisted fuel cell systems with lowand medium temperatures.
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System performance of solar water heaters depends upon collector and storage tank designs, solar radiation intensity and ambient temperature, amongst others. Evacuated glass tube collectors with U-tubes inside are less prone to leakages than the all-glass or the heat pipe types. U-tube solar water heaters suspended on walls and balconies could help overcome present day roof space restriction and increasing apartment-style housing. As such, their performance would depend upon its orientation when mounted in a vertical position. This paper reports the results of outdoor tests conducted on natural convection U-tube solar water heaters oriented towards different directions. Long and short term test procedures were employed to allow us to compare their performances as if they were tested simultaneously side-by-side.
文摘New alternatives and inventive renewable energy techniques which encompass both generation and power management solutions are fundamental for meeting remote residential energy supply and demand today, especially if the grid is quasi-inexistent. Solar thermoelectric generators mounted on a dual-axis sun tracker can be a cost-effective alternative to photovoltaics for remote residential household power generation. A complete solar thermoelectric energy harvesting system is presented in this paper for energy delivery to remote residential areas in developing regions. To this end, the entire system was built, modeled, and then validated with the LTspice simulator software via the thermal-to-electrical analogy schemes. Valuable data in conjunction with a novel LTspice circuit were obtained, showing the achievability of analyzing transient heat transfer with the SPICE simulator; however a few of the problems to be solved remain at the practical level. Despite the unusual operation of the thermoelectric modules with the solar radiation, the simulation and measurements were in good agreement, thus validating the new modeling strategy.
文摘The MPPT （maximum power point tracking） is one of the most important features of a regulator system that processes the energy produced by a photovoltaic generator. It is necessary, in fact, to design a controller that is able to set the output value of the voltage and ensure the working within the maximum power point. In this paper, we propose the application of the robust sliding mode control technique to a DC-DC buck converter which is combined with a classical P ＆ O （perturbation and observation） algorithm to enhance the solar system efficiency. Dynamic equations describing the boost converter are derived and a sliding mode controller for a buck converter is designed. It is shown that, this control approach gives good results in terms of robustness toward load and input voltage variations. The effectiveness of the proposed work is verified by the simulation results under PowerSim environment.
文摘Solar thermal propulsion system includes solar thermal propulsion and nuclear thermal propulsion, and it is a significant issue to improve the heat transfer efficiency of the solar thermal thruster. This paper proposes a platelet configuration to be used in the heat exchanger core, which is the most important component of solar thermal system. The platelet passage can enhance the heat transfer between the propellant and the hot core heated by the concentrated sunlight. Based on fluid-solid coupled heat transfer, the paper utilized the platelet heat transfer characteristic to simulate the heat transfer and flow field of the platelet passage. A coupled system includes the coupled flow and heat transfer between the fluid region and solid region. The simulation result shows that the propellant can be heated to the design temperature of 2300K in platelet passage of the thermal propulsion system, and the fluid-solid coupled method can solve the heat transfer in the platelet structure more precisely.
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the National Natural Science Foundation of China(Grant Nos.41274174,41422405,41274169&41421063)the Fundamental Research Funds for the Central Universities(Grant No.WK2080000077)
文摘In the solar atmosphere, there exist two frequently-observed phenomena, Moreton waves and EIT(extreme-ultraviolet imaging telescope) waves, whose physical nature is still under debate. In this work, we perform a three-dimensional ray-tracing simulation for the propagation of fast magnetoacoustic waves. We build a stratified solar atmosphere model and take partial ionization into consideration to give an exact description of chromosphere and transition region. The calculated result is compared with a flare event observation in which both Moreton waves and EIT waves were present. In agreement with observations, the calculated wavefront show different kinematical characteristics in different propagation directions during different times.Moreton waves and EIT waves have higher propagation speeds near the active region where the magnetic field strength is strong. The result suggests that both Moreton waves and EIT waves of this event can be interpreted as the fast magnetoacoustic waves propagating at different heights in the solar atmosphere.
