Experimental Study On The Enhancement Of Micro-pillars To The Heat Transfer Performance Of Gravity Heat Pipe With Flat Plate Evaporation Chamber

As an efficient heat transfer element,gravity heat pipe is widely applied to heat transfer application fields in industry due to its simple structure,convenient manufacture,low cost in production.With the aggravation of the energy crisis and the deterioration of environmental problems,all countries around the world have begun to focus on energy conservation and emission reduction.And the intensified research on heat transfer capacity of gravity heat pipe has become a hot topic in the research of gravity heat pipe.The research status of gravity heat pipe was reviewed in this article.And the existing research can be divided into three aspects:theoretical analysis,numerical simulation and experimental research.And the experimental research was chosen as the main research method by most researchers.It was found that the research on gravity heat pipe mainly focused on the change of variety and the amount of working fluid or the production of the capillary core.But the performance of heat pipe with micro-structures which can be simply produced has seldom been referred.Therefore,the structure of gravity heat pipe was modified and optimized in this article.An evaporation chamber was designed and micro-pillars were processed in evaporator section in order to enhance heat transfer.The method of experimental research was chosen in order to investigate the effect of micro-pillars with different sizes on the heat transfer performance of gravity heat pipe.The main work are as follows:The current research status and the operating principle of gravity heat pipe was summarized in this article.The gravity heat pipe with flat plate evaporation chamber combined with different sizes of micro-pillars was designed and processed.The experimental platform for the measurement of gravity heat pipe heat transfer performance was designed and constructed.The experimental scheme and experimental process and the processing method of experimental data were decided.The effect of different sizes micro-pillars on the start-up time and start-up temperature of the gravity heat pipe with flat plate evaporation chamber in the process of cascade start-up were comparatively analyzed by method of experiment.The results showed that the start-up time and start-up temperature of gravity heat pipe were all lower than those of gravity heat pipe with smooth flat evaporation surface.When the heat flux was 68.6 W/cm~2,the start-up time of heat pipe with micro-pillars width of 0.2 mm and height of 0.8 mm was shorten by 57.1%compared with that of gravity heat pipe with smooth flat evaporation surface,and the start-up temperature was reduced by 28%.When the micro-pillars width was small,the gravity heat pipe with higher micro-pillars had shorter start-up time and lower start-up temperature.With the increase of micro-pillars width,the effect of the variety of micro-pillars on start-up time of heat pipe decreased gradually.However,the start-up temperature of heat pipe increased firstly and then decreased with the increase of micro-pillars height only at higher heat flux.The variety of micro-pillars width had different effects on the start-up time and start-up temperature of heat pipe at different heat flux when the micro-pillars height was different.But wider micro-pillars were conducive to reducing the start-up time of heat pipe at higher heat flux.The heat transfer performance of the gravity heat pipe with flat plate evaporation chamber was analyzed from four aspects of the evaporator section wall temperature and superheat,working pressure,heat transfer coefficient of evaporator section and total thermal resistance.The effect of different micro-pillars heights and widths on the heat transfer performance of gravity heat pipe with flat plate evaporation chamber at different heat flux was comparatively analyzed.The results showed that the heat transfer performance of gravity heat pipe with micro-pillars was significantly improved.When the heat flux was68.6 W/cm~2,the heat transfer coefficient in evaporator section of heat pipe with micro-pillars width of 0.2 mm and height of 0.8 mm was ingcreased by 117.7%compared with that of gravity heat pipe with smooth flat evaporation surface,and the total thermal resistance was reduced by 48.9%.When the micro-pillars width was lower,higher micro-pillars were beneficial to enhance the heat transfer performance of heat pipe.The heat pipe with higher micro-pillars had lower evaporator section wall temperature and superheat and total thermal resistance and higher heat transfer coefficient of evaporator section.When the width of micro-pillars increased,the variety of micro-pillars height had less and complex influence on the heat transfer performance of gravity heat pipe.When the height of micro-pillars was lower,the increase of micro-pillars width was conducive to decreasing the evaporator section wall temperature and superheat and total thermal resistance and increasing the heat transfer coefficient in evaporator section.When the height of micro-pillars increased,the variety of micro-pillars width had little or no effect on the evaporator section wall temperature and superheat,heat transfer coefficient in evaporator section and total thermal resistance.