The technology of small point-focusing concentrator of solar energy has been developing rapidly in recent years owing to its compact structure and high collecting efficiency. This report presents important development...The technology of small point-focusing concentrator of solar energy has been developing rapidly in recent years owing to its compact structure and high collecting efficiency. This report presents important developments of small point-focusing concentrator in the past decade. This kind of solar concentrator refers to the parabolic dish concentrator, the point-focusing Fresnel lens, and the Scheffler reflector. Technological advances of these concentrators and the related performances have been presented. There are three main mirror fabrication technologies for dish concentrator, which are high polishing metal, silver-glass mirror and vacuum-membrane. Polymethyl methacrylate is widely used as material in Fresnel lens. Many scholars have proposed new lens shape to improve the uniformity of focusing. The Scheffler reflector has a characteristic of fixed focus, but its design parameters are not perfect so current research focuses on the theoretical calculation of the mirror. In addition, typical applications of the small point-focusing concentrator in photovoltaic system, solar thermal system, solar chemical system, and day-lighting system are summarized. Upon listing the important publications in open literature, a category of main applications of such kind of solar collector is provided based on the working characteristics of the system.展开更多
The laminar heat transfer in the thermal entrance region in round tubes, which has a variable surface heat flux boundary condition, is analytically studied. The results show that the heat transfer coefficient is close...The laminar heat transfer in the thermal entrance region in round tubes, which has a variable surface heat flux boundary condition, is analytically studied. The results show that the heat transfer coefficient is closely related to the wall temperature gradient along the tube axis. The greater the gradient, the higher the heat transfer rate. Furthermore, the coordination of the velocity and the temperature gradient fields is also analysed under different surface heat fluxes. The validity of the field coordination principle is verified by checking the correlation of heat transfer coefficient and the coordination degree. The results also demonstrate that optimizing the thermal boundary condition is a way to enhance heat transfer.展开更多
基金sponsored by the National Key Basic Research Program of China (No. 2015CB251303)
文摘The technology of small point-focusing concentrator of solar energy has been developing rapidly in recent years owing to its compact structure and high collecting efficiency. This report presents important developments of small point-focusing concentrator in the past decade. This kind of solar concentrator refers to the parabolic dish concentrator, the point-focusing Fresnel lens, and the Scheffler reflector. Technological advances of these concentrators and the related performances have been presented. There are three main mirror fabrication technologies for dish concentrator, which are high polishing metal, silver-glass mirror and vacuum-membrane. Polymethyl methacrylate is widely used as material in Fresnel lens. Many scholars have proposed new lens shape to improve the uniformity of focusing. The Scheffler reflector has a characteristic of fixed focus, but its design parameters are not perfect so current research focuses on the theoretical calculation of the mirror. In addition, typical applications of the small point-focusing concentrator in photovoltaic system, solar thermal system, solar chemical system, and day-lighting system are summarized. Upon listing the important publications in open literature, a category of main applications of such kind of solar collector is provided based on the working characteristics of the system.
文摘The laminar heat transfer in the thermal entrance region in round tubes, which has a variable surface heat flux boundary condition, is analytically studied. The results show that the heat transfer coefficient is closely related to the wall temperature gradient along the tube axis. The greater the gradient, the higher the heat transfer rate. Furthermore, the coordination of the velocity and the temperature gradient fields is also analysed under different surface heat fluxes. The validity of the field coordination principle is verified by checking the correlation of heat transfer coefficient and the coordination degree. The results also demonstrate that optimizing the thermal boundary condition is a way to enhance heat transfer.
