Thermal Hydraulic Research And Optimal Design Of Plate-fin Heat Exchangers For Helium Refrigerators

As a key equipment in helium refrigerator,the heat exchanger plays an important role in heat exchange to reduce the helium gas from room temperature to liquid nitrogen,liquid helium and even superfluid helium temperature.In order to cope with the future construction of large-scale refrigerator as well as the standardization and serialization of domestic helium refrigerator,it’s required that the heat exchanger can achieve the sufficient heat transfer ability in the compact space.This paper studies the serrated plate-fin heat exchanger in helium cryogenic system:1.The heat transfer and pressure drop performance of serrated fins is studied by CFD simulations;Through the volume quality factor,the comprehensive ability about sufficient heat transfer in the compact space is measured.Therefore,the effect of structural factors on the performance is analyzed quantitatively;For the fin type of 47JC1402 and 65JC1403,the performance of helium gas flowing through the fin surface at room temperature,liquid nitrogen and liquid helium temperature conditions is studied by CFD.Then the difference of fin performance is also illustrated;In order to reduce the error of the correlation formula fitting,the kriging spatial interpolation model based on the 264 groups of data available in the open literature is established to predict the general performance of serrated fin surface.2.The experimental setup about the performance of fin cores for the domestic commonly used three types of serrated fins and one type of perforated fins is established using low temperature helium as working medium.Based on this,the heat transfer and pressure drop characteristic curves of the helium gas flowing through the fin channel are obtained;Compared with the performance test of normal temperature helium,the fin performance differences at different temperature conditions are analyzed with the aid of simulation results;Various fin performance prediction model is analyzed and the results show that the CFD simulation can predict the fin performance accurately by combining actual fin structures and operating conditions.3.Based on the first law of thermodynamics,the distributed parameter model of multi-stream recuperative heat exchanger considering variable physical properties,axial heat conduction,heat leakage from surroundings is established.Subsequently,the performance deviation under the cryogenic conditions from the original design conditions is discussed and the effect of various additional factors that affect the heat exchanger performance is analyzed;To supplement the ability of the commercial software Aspen MUSETM employed in the helium refrigerators,the model can calculate the heat leakage value according to the specific conditions and give the temperature and pressure field in detail;Based on the distributed parameter model,the additional losses of the first stage of heat exchanger in the EAST helium refrigerator under the actual cryogenic conditions are revealed.Meanwhile,the heat load distribution influenced by the radiative parasitics on the surface of the heat exchanger,the axial heat conduction distribution at each layer and excess thermal load distribution under established channel arrangement are achieved.This can provide theoretical guidance for the optimization of heat exchanger,on-site assembly and adiabatic ways.4.For the first stage of plate-fin heat exchanger in the 5kw@4.5K helium refrigerator,the optimization of the heat exchanger’s volume is carried out based on hybrid genetic algorithm within the constraints of heat exchange requirements,maximum allowable pressure drop,existing manufacturing techniques and structural strength.The results show that the optimization results can greatly reduce the size,reduce the manufacturing cost and the installation space under the constraints of many practical constraints compared with the original design scheme.In conclusion,the surface performance of low-temperature helium gas flowing through the serrated fins is studied in this paper,which lays a theoretical foundation for the design and development of heat exchangers;The influence mechanisms about low temperature additional losses are revealed,which can provide the reference and guide for the design of heat exchangers;The design process of heat exchanger is optimized,which can reduce the size of heat exchanger,cut the manufacturing cost and shorten the development cycle.