Experimental Study Of Start-up Performance Of Solar Heat Pipes

As a new type solar heat collector, heat pipe vacuum-tube solar heat collector combines the high heat collecting efficiency of the glass vacuum-tube and high thermal conductivity of heat pipes, avoiding many problems which appear in the normal type solar collectors. In order to solve the aitfreeeze broblem of the solar heat pipes, our research group proposed the use of mixture working fluid (water and ethanol) instead of a single working fluid (water), studied the effect of concentration of working fluid, liquid filling ratio, inclination angle, heating power on the solar heat pipe heat transfer performance Whether the heat pipe can start-up quickly to work stablely is very important for the practical application of heat pipe. In this paper, on the base of previous work of our research group, the experimental research work of start-up performance of the solar heat pipe was carried out.This paper designed and constructed a convenient integration vacuum and filling system of heat pipe, developed a novelty way to produce the heat pipe with good performance. Working fluid was evaporated and condensated repeatedly to eliminate the non-condensable gas completely and capillary copper pipe was used as process pipe to mechanical seal the heat pipe under positive pressure when the heat pipe is heating.The effect of of the concentration of working fluid, heat pipe inclination angle, evaporation temperature, non-condensing gas on the start-up performance of heat pipe was studied on the base of experiment, and conclusion was drew as bellowing:(1) The effect of concentration of working fluid on the start-up performance of heat pipe at the low and high evaporation temperature is fundamentally different.a At the low evaporation temperature(40℃, 50℃), the main effect of the the condensation heat released on the condensation section is working fluid's latent heat. The pure water heat pipe's start-up performance is best, and the heat pipe's start-up performance reduces as the ethanol concentration increasesb At the high evaporation temperature(70℃), the main effect of the the condensation heat released on the condensation section is working fluid's evaporation. The pure ethanol heat pipe's start-up performance is best, and the heat pipe's start-up performance increases as the ethanol concentration increases(2) The best heat pipe inclination angle is 45°, a suitable range of inclination angle is among 30°~ 60°, the worst. heat pipe inclination angle is 90°.(3) Studed the effect of evaporation temperature on the start-up performance of heat pipe: Heat pipe start-up time has a linear inverse relationship with evaporation temperature, while heat pipe condesation setion temperature has a linear proportional relationship with evaporation temperature.(4) Non-condensing gas seriously affected the start-up performance of heat pipe, it often leads to a failure start. We must ensure the tightness of the heat pipe in heat pipe production process and elimination of non- condensing gas.