Thermal Analysis And Experimental Study Of The Cryocooler And Low Temperature Loop Heat Pipe System

Highly reliable cryocoolers and effective heat conducting elements are crucial in satellite across-gimble and multiple heat source cryogenic cooling systems.Generally speaking,the Stirling type pulse tube cryocooler(PTC)is featured with high structural reliability,easy handling and long lifetime.Upon that,it has the advantages of low electromagnetic interference,low vibration and high structural support strength at the cold trip.Meanwhile,the cryogenic loop heat pipe(CLHP),a highly effective two-phase flow heat transfer component,has no moving parts,which means that it can achieve efficient heat transfer as well as long lifetime and high reliability.The combination of these two technologies can meet the large cooling capacity,long distance and small temperature difference heat transfer need in the spacecraft and cryogenic optical thermal control system.In this article,thermal analysis and experimental results of the PTC,the CLHP and the grooved heat pipe integrated heat transfer system are introduced,as well as their applications and future prospects.The transient analysis model of the CLHP and its heat load is obtained.This research can help to assist system design as well as improve the understanding of the working characteristics of the CLHP and the grooved heat pipe.At first,this article introduces the design and the thermal analysis of the integrated system.The CLHP including a wick structure with nickel sintered porous material and a microchannel condenser are selected.The split PTC used in this paper is the coaxial cold finger structure.To solve the two-phase flow heat transfer calculation,a one-dimensional model has been made.The transient operating characteristics of the CLHP and the integrated system are analyzed,which includes the cooling process and steady state calculation with different external heat flow and heat load,periodically changing external heat flow response and so on.The results show that the temperature difference of the CLHP decreased first then increase with the increase of the input power.The condensing capacity of the condenser has a great influence on the CLHP temperature difference,and the two-phase region of the condenser increases with the increase of the input power,thus enhancing the heat transfer capacity of the condenser and reducing the thermal resistance of the CLHP.The CLHP is in the "variable heat resistance zone" when the heat capacity is more than 40 W,otherwise it is in the "fixed heat resistance zone".By reducing the thermal resistance between the heat load and the evaporator,the heat pipe temperature difference and the total temperature difference reduce.The integrated system has effective response to the changing external heat flow.The formulas for calculating the cooling capacity and the off-state heat leak of the PTC are summarized,which provide the theoretical guidance for the system design.To validate the model,a detachable cryogenic vacuum experiment platform is built,and the coupled characteristics with periodic changed external heat flow of the system is experimentally studied.The cooling characteristics of the CLHP and heat load system are in good agreement with the simulation.It is found that the temperature and the gas-liquid state in the CLHP evaporator have a great influence on the start of the CLHP.The cooling down velocity of the system is mainly affected by the external heat flow.At the same time,the liquid pipe leakage,the relative position of the compensation chamber and the evaporator of the CLHP cannot be ignored on the ground experiment.Further more,according the theoretical and experimental research above,this article optimize the coupling structure of the PTC's cold trip and the structure of the heat pipe gas pipeline.The temperature difference between heat pipe evaporator and condenser is 15.4K with the heat load of 40 W at the temperature of 170 K after optimization.The temperature difference of cold trip coupled structure is 3.7K,and heat transfer distance can reach 1.3m.Finally,to ensure the orbit reliability of the CLHP and PTC coupled system,the grooved heat pipe are applied and experimental studied as a redundant structure of the system.The experimental results show that the heat transfer performance of the LHP and the grooved heat pipe are different,which is the key reason that the CLHP cannot start regularly when working with the grooved heat pipe.In this paper,we add a flexible belt connection between the grooved heat pipe evaporator and the heat source.Such structure can improve the co-operation characteristics and flexibility of the redundant system,but it can also increase the system temperature difference.The future study needs to focus on solving this problem.