Study On Efficient Heat Transfer Performance Of Pulsating Heat Pipe At Liquid Hydrogen Temperatures

The development of cutting-edge technologies such as space detectors,cryogenic propellants,and quantum computing has put forward new requirements for cryogenic heat transfer technology.There are three main types of cryogenic heat transfer technologies:conduction using metals,convection based on gas-liquid flow,and phase change heat transfer based on evaporation and condensation.The heat transfer efficiency of phase change is 1 to 2orders of magnitude higher than the heat transfer efficiency of the former two.The pulsating heat pipe combines convection heat transfer and phase change heat transfer.It not only has the characteristics of high thermal conductivity,light weight and no power consumption like traditional heat pipes,but also has unique advantages such as simple structure,flexible layout and ability to operate under microgravity.Studies have shown that cryogenic pulsating heat pipes have excellent thermal performance.However,the existing research is not enough.There is a lack of in-depth understanding in the following three aspects: the particularity of cryogenic pulsating heat pipes compared with room temperature pulsating heat pipes,mathematical models used to analyze the flow and heat transfer characteristics of cryogenic pulsating heat pipes,and the influence of key parameters on heat transfer characteristics.This paper aims at the application requirements of the pulsating heat pipe in the liquid hydrogen temperature range and the unresolved scientific problems.The theoretical and experimental researches on the thermal performance of the pulsating heat pipe in the liquid hydrogen temperature range have been carried out.The main works are as follows:1.The physical properties of the cryogenic working fluids,the temperature dependence of the filling ratio and the non-ideality of the cryogenic gas are analyzed,showing that the cryogenic pulsating heat pipe is different from the room temperature pulsating heat pipe.There is a big difference between the cryogenic working fluids and the room temperature working fluids,which will lead to differences in the driving force,phase change frequency and heat transfer efficiency.The T-v diagram of the working fluid is used to show the variation of the filling ratio with temperature and its significance at cryogenic temperatures.The temperature dependence of the filling ratio of the room temperature working fluids is not significant,so their filling ratio can be regarded as a constant.In addition,the limitations of the ideal gas hypothesis in the cryogenic temperature region are analyzed,and the applicability and convenience of the RKS equation of state in the liquid hydrogen temperature range are explained.2.Considering the non-ideality of cryogenic working fluids,the real gas equation of state(RKS equation of state)is used to modify the gas pressure,energy equation and saturated properties,and the one-dimensional plug flow model is extended to the liquid hydrogen temperature range.The characteristics of the heat transfer of the pulsating heat pipe are analyzed using the modified model.The flow characteristics,temperature distribution,pressure distribution and thermal resistance distribution of the pulsating heat pipe from startup to stable operation are obtained.The contribution of latent heat and sensible heat to the total heat transfer is compared.It is pointed out that the pulsating heat pipe has considerable sensible heat transfer on the basis of latent heat transfer.3.The experiment was carried out by using the controlled variable method to systematically reveal the influence of key parameters on the startup characteristics and steady-state thermal performance of the pulsating heat pipe.10 sets of experiments,452 working conditions have been designed and carried out.The validity of the theoretical model is verified in terms of steady-state temperature and pressure,transient temperature and pressure,and the effect of heat load mode.The influences of filling ratio,heat load,condenser temperature,number of turns and heat transfer distance on thermal performance are explored.Finally,the empirical correlation is fitted,which can predict the heat transfer performance data in this study and the literature very well,and the deviation of the fitting is ±20%,which is better than the existing correlation in the literature.