Experimental Investigation On Thermal Contact Resistance In Grooved Heat Pipe Heat Transfer System

Heat pipe is a kind of heat transfer device by evaporation,condensation phase transformation to make working fluid to circular flow,and the evaporation thermal resistance and condensation thermal resistance of working fluid in heat pipe cavity are both very small,so heat pipe can transfer large quantity of heat without producing big temperature difference.Heat pipe technique has been widely used in satellite thermal control system,which application can figure out heat dissipation and thermal control of heat production devices which generate high heating flux and make satellite temperature uniformity,and provide safeguard for enhancing the level and reliability of satellite thermal control.Furthermore,heat pipe has some prominent features,such as compact structure,without motion parts,without consuming energy,and so on,which is the reason why heat pipe technique has already been an important one in space passive thermal control.On account of unique heat transfer characteristic,―Ω‖ shape axial grooved heat pipe has been frequently used in satellite thermal control systems.As an significant heat transfer part,heat pipe is connected with heat source and heat sink by some certain ways,which transfers heat generated by heat source to heat sink to dissipate to outerspace,so contacts between heat pipe and heat source and heat sink are key to heat pipe heat transfer performance,which have some relationship with joint conditions,implementation process,and thermal resistance caused by contact is usually called thermal contact resistance.So,according to the actual situation of the applications,some theoretical analysis about thermal resistance in heat pipe heat transfer system is carried out in the article,and the thermal resistance is divided into two parts,thermal resistance of heat pipe itself and thermal contact resistance.In this paper,the experimental investigation on the thermal contact resistance influencing heat pipe heat transfer performance was carried out.The factors influencing the thermal contact resistance included the screw torque,the screw density,the filler and its heat transfer performance between contact surfaces,the heat flux,and thermal environment(vacuum and atmospheric environment).Test apparatus were respectively designed and constructed to measure thermal contact resistance of single grooved heat pipe in atmosphere environment and double grooved heat pipe in heat transfer system in atmosphere environment and in vacuum condition.The effect of a single factor influencing and multiple factors influencing on the heat transfer performance were tested on some certain grooved heat pipe heat transfer system to provide technical support for the optimization of the heat pipe installation process in engineering applications.Mainly include the following:1)The mechanical partialstructure of the heat pipe was simulated and the influence of the installation screw parameters and the thickness of the fin on the deformation and contact pressure of the mounting surface were analyzed.In the allowed torque range of the screw,for the single grooved heat pipe,the greater the torque,the greater the average contact pressure,the greater the separation of the nodes of characteristic line L1 and W1 on the fins from the mounting plate;The average contact pressure of the fin thickness 0.8 mm is greater than that of the fin thickness 1.0 mm and 1.2 mm,so was the separation of the nodes of characteristic line L1 and W1 on the fins from the mounting plate;when the distance between two screw holes was changed from 80 mm to 40 mm,the contact pressure was increased,so was the separation of the nodes of characteristic line L1 and W1 on the fins from the mounting plate;For the double grooved heat pipe,the greater the screw torque,the greater the average contact pressure,and the closer the contact of the nodes the characteristic lines L1 and W1 on the fins with the mounting plate;when the distance between two screw holes was 90 mm,the average contact pressure of the fin thickness 0.8mm was larger compared with two other fin thickness,the nodes of the characteristic lines L1 and W1 on the fins are in better contact with the mounting plate when the fin thickness was 1.2mm;when the distance between two screw holes was changed from 90 mm to 45 mm,characteristic line L1 and the characteristic line W1 and the mounting surface could in better contact;as fin thickness changed,the average contact pressure changed little.2)An experimental investigation about room temperature single grooved heat pipe heat transfer system was carried out in the atmosphere under different mounting conditions,studies had shown that,in the range of thermal load applied to the system,temperature of the hot mounting surface and the cold mounting surface was increased with heat load increasing;the temperature distribution of mounting surfaces was different with different interface materials;when TPG was used as the interface material,the temperature uniformity of the mounting surface was better than that of the heat-conducting pad;For the same interface material,with the increase of the heat load,heat pipe mounting surfaces temperature difference,Heat Pipe total temperature difference,heat pipe body and fin temperature difference,heat pipe body temperature difference and heat pipe heat transfer system total temperature difference were increased,and thermal contact resistance of mounting surfaces of heat pipe were reduced when the heat flux was increased,and the thermal contact resistance of the hot mounting surface was larger than that of the cold mounting face;the entire system heat transfer temperature difference was smaller when TPG as the interface materials,so was the total thermal resistance in the heat transfer system;the change trend of the thermal contact resistance of the heat pipe mounting surface with the screw torque was not as obvious as of as that of the heat load;with the heat flux increasing,the thermal contact resistance of single grooved heat pipe mounting surfaces were increased.3)An experimental investigation about room temperature double grooved heat pipe heat transfer system was carried out to mainly compare the hot mounting interface temperature,heat pipe total thermal resistance,the hot mounting thermal contatc resistance,cold mounting thermal contact resistance with different torques and heat loads and without any interface fillers in under atmosphere and vacuum conditions.The experimental results indicated that environment had a certain effect on heat pipe heat transfer system,the thermal contact resistance of heat source mounting surfaces in vacuum was more than that in the atmosphere,and so was the thermal contact resistance of heat sink mounting surface.The thermal contact resistance was influenced by screw torque,heat sink mounting surface thermal contact resistance with the screw torque 0.4 Nm was about 2.4 times of that with the screw torque 1.2 Nm in the same environment and the same heat load,and the reason for the difference in thermal contact resistance between the vacuum and the atmospheric environment was analyzed by calculating the thermal conductivity of the gap gas;the experimental results of different heat load and different screw torque in four different mounting ways were compared about the double grooved heat pipe heat transfer system in the vacuum environment,we can see that the heat transfer performance of the whole heat transfer system without any interface material between the contact surface was the worst;the thermal contact resistance of the heat pipe heat transfer system and the total thermal resistance of the system could be reduced by using thermal-conductive pad and PGS attached to the heat pipe wall or increasing the number of screws mounted in the heat pipe;and the mounting surface thermal resistance of the double grooved heat pipe changed little with the heat flux density;the heat transfer performance of the heat pipe heat transfer system when the heat pipe was connected with the different size honeycomb panel in the vacuum environment was studied,and it was found that the heat transfer performance of the system was better when using the honeycomb panel HC1.