Simulation And Experimental Study On JT Cryocooler Driven By A Single Stage Linear Compressor At Liquid Helium Temperatures

The precooled JT cryocooler(JTC)has become the main cooling technology at liquid helium temperatures for space use,this thesis carries out the following work: 1)A heat exchanger(HE)model that includes property variations,axial conduction,and radiation heat leak is improvedBased on the energy balance,a one-dimensional numerical HE model is improved.the performance differences of the HEs use different materials are calculated,indicating that excessively high axial conduction can deteriorate the HE performance at low temperatures.Radiation heat leak has a great influence on HE with small heat exchange capacity in low temperatures.A performance test setup of HE is built,the test results verify the accuracy of the model.2)A JTC process simulation that considers actual conditions is builtBased on HE numerical model,the actual performance model of the compressor obtained by external parameters,and the empirical formula of the Stirling cryocooler,a complete model method for JTC at liquid helium temperatures is built.The effects of the secondary precooled temperature and pressure ratio on the cooling capacity,precooled capacity and COP driven by different compressor are compared,indicating that the actual performance of the compressor can affect the optimization of the operating parameters.For a given cooling capacity,a set of design values of pressure ratio and precooled temperature with high efficiency are obtained.This method can provide suggestions for the optimal operating parameters of the JTC.3)The closed cycle experiment with small pressure ratio shows the JTC has adaptive characteristicsThe closed experiment of JTC driven by a valved single-stage linear compressor and precooled by 2-stage GM cryocooler is tested at three pressure control patterns.Unlike the open cycle,when the system pressure conditions are not controlled or only the low pressure is controlled,JTC has adaptive characteristics.The proportion of gas phase in the system increases along with the increase of thermal load,which improves the cooling capacity.When the precooled temperature is fixed at 7.3 K,experiment result shows that the maximum cooling capacity is 87.98 mW at 4.9 K while the compressor of JT side consumes 41.6 W electrical power.