Experimental Study On Heat Transfer Characteristics Of Two-phase Closed Thermosiphon Under Variable Operating Conditions

The two-phase closed thermosyphon,or gravity heat pipe,is a phase change heat transfer element with ultra-high thermal conductivity.With the country’s concern about how to reduce energy consumption,it has been widely used in industrial waste heat recovery,electronic equipment cooling,geothermal utilization,solar energy utilization and other fields.Through a large amount of consulting and reading domestic and foreign literatures to understand the current status of gravity heat pipe research,scholars mainly conduct research from three aspects: theoretical research,experimental research,and numerical simulation.This article takes three gravity heat pipes of stainless steel-acetone,stainless steel-water,and stainless steel-methanol as the research objects.Based on the research status of gravity heat pipes and the theory of gravity heat pipe heat exchange,the design and manufacture of gravity heat pipes,the design of experimental programs,and the establishment of experimental platforms,By changing the parameters such as the length of the evaporation section,the condensation section and the heating power,the influence on the heat transfer performance of the gravity heat pipe is analyzed;at the same time,the start-up and isothermal experiments are carried out on the three heat pipes to analyze the relationship between the gravity heat pipes of different liquid-filled working fluids difference.Through comparative analysis of experimental data,the following conclusions are drawn:1.Experiments were carried out on the variable evaporation section of three liquid-filled working fluid gravity heat pipes,and it was found that the change in the length of the evaporation section affected the heat transfer capacity,condensation section heat transfer coefficient,and overall thermal resistance of the three liquid-filled working fluid gravity heat pipes.The effect remains the same.The heat exchange of stainless steel-acetone and stainless steel-methanol gravity heat pipes is optimized when the length ratio of the condensation section of the evaporation section is 1: 1.29,and the gravity of the stainless steel-water gravity heat pipe is 1: 1.125 when the length ratio of the condensation section of the evaporation section is 1: 1.125 The overall heat transfer performance of the heat pipe is optimal.2.Experiments were carried out on the variable condensing section of three liquid-filled working fluid gravity heat pipes,and it was concluded that the change in the length of the condensing section affected the heat transfer coefficient of the three liquid-filled working fluid gravity heat pipes in the evaporation section,the condensation section heat transfer capacity,and the overall thermal resistance.The impact is consistent.The stainless steel-acetone gravity heat pipe achieves the best heat transfer when the length ratio of the condensation section of the evaporation section is 1:1.67,and the gravity heat pipe of stainless steel-water and stainless steel-methanol gravity when the length ratio of the condensation section of the evaporation section is 1:1 and 1: 1.5 The overall heat transfer performance of the heat pipe is optimal.3.A prediction formula is proposed for the overall thermal resistance of the gravity heat pipe,and empirical formula fitting is carried out for the heat pipes of the three liquid-filled working fluids under the conditions of variable evaporation section and variable condensation section,and the corresponding formula is obtained.Good,can predict the thermal resistance of different working conditions.4.Experiments were conducted on the start-up and isothermal properties of three liquid-filled working fluid gravity heat pipes,and it was found that the stainless steel-acetone gravity heat pipe had the shortest start-up time and the best isothermality,followed by stainless steel-methanol gravity heat pipe,and stainless steel-water gravity heat pipe.Has the longest start-up time and the worst isotherm,and the wall temperature fluctuates periodically.5.A comparative analysis of the overall heat transfer performance of the three liquid-filled working fluid gravity heat pipes and the corresponding suggestions are made,and the heat exchange coefficient of the gravity heat pipe is obtained: acetone working fluid> methanol working fluid> water working fluid...