Numerical Simulation And Experimental Study On Heat Transfer And Pressure Drop Performance Of 2K-4K Sub-atmospheric Heat Exchanger

Temperatures below 2K can be obtained by using superfluid helium cooling method,which is beneficial to the superconducting equipment to obtain higher current and stronger magnetic field.Nowadays,superfluid helium has been used more and more extensively in the cooling of superconducting magnets and superconducting accelerating cavities.As the core components of the superfluid helium cryogenic system,the sub-atmospheric heat exchanger is the key factor that affecting the liquid ratio of superfluid helium.The structure and pressure drop performance of the sub-atmosphere heat exchanger determine the energy consumption of the vacuum pump system.Therefore,the study of heat transfer technology and pressure drop performance of sub-atmosphere heat exchanger is of great significance for the design and optimization of superfluid helium system,which has theoretical significance and application value.This paper studied the heat transfer performance and structural modification design of negative pressure heat exchanger.The main research contents are as follows:(1)In this paper,the design methods of sub-atmospheric heat exchanger was studied firstly.For the laminated-finned type and the tube-finned type heat exchanger,the ε﹣NTU method was used to calculate the structural parameters.The influence of structure parameters on the size of heat exchanger is analyzed.Then,the heat transfer efficiency and pressure drop were checked by using empirical formula.According to the design results,a three-dimensional geometric model was established for the following study.(2)Secondly,numerical simulation software ANSYS CFX was used to calculate the distribution of temperature field,pressure field and flow field in the sub-atmospheric heat exchanger.The change law of heat transfer efficiency and pressure drop with the flow rate of working medium was obtained.Then the simulation results was compared with the experimental data of the same type of sub-atmospheric heat exchanger.The simulation results are in good agreement with the experimental data.(3)According to the flow field pattern of the laminated-finned type heat exchanger,the fin structure parameters and its arrangement mode was adjusted reasonably.The results show that compared with the original structure,the size and number of secondary vortices in the flow field can be significantly increased by optimizing the fin holes,gaps between fins the fin arrangement mode.The efficiency of the sub-atmospheric heat exchanger was thus improved 15.97%.(4)Based on 2K cryogenic vertical test platform in IMP CAS,experiment research was carried out to study the performance of the laminated-finned type heat exchanger.The experimental results show that the heat transfer efficiency is up to 82.29% at the mass flow rate of 3.5076g/s,which meets the design requirement.