Numerical Simulation And Experimental Research Of Hampson-type Finned Tube Heat Exchanger

Miniature Joule-Thomson cryocoolers have been widely used for rapid cooling of infrared detectors,cryosurgery probes,thermal cameras,and missile guidance homing systems,due to their special features of simple configuration,compact structure and rapid cooldown characteristics.The thermodynamic performance of the J-T refrigerator depends upon the hydraulic and heat transfer characteristics of the recuperative heat exchanger.At present,compared with international advanced technology,the domestic research on miniature J-T cryocooler was still in the initial stage,which restricted the domestic develpoment of the J-T cryocooler.In the present work,based on the numerical model of finned-tube heat exchanger,an effectiveness-NTU approach is adopted to predict the thermodynamic behaviors of the heat exchanger for the Joule-Thomson refrigerator with variable working conditions.The J-T cooler testing facility is used to verify the above numerical model,and the experimental research on some parameters than can not be obtained by numerical simulation is also carried out.Then we have a single factor optimization for the finned-tube heat exchanger,and optimized it by using response surface methodology.Last,The genetic algorithm is used to optimize the available work loss and the ideal cooling capacity to enhance the thermodynamic peformance of the heat exchanger.Our research provides a new approach for the design of hampson type J-T cryocooler.Main research contents and conclusions could be summarized as follows:(1)Taking into account the effect of the geometry of the flow channel,the variation of the fluid's property and the flow maldistribution,a steady-state numerical model of hampson type J-T cooler is established.The thermodynamic characteristics of the cryocooler are numerically done by ourselves,using EES software based on finite difference method.And then,the experimental platform was set up to verify the correctness of the numerical model.(2)Temperature distribution and Pressure distribution for high and low pressure streams in the heat exchanger was calculated by the numerical model,and the flow and heat transfer in the heat exchanger are analyzed in detail,include thermal resistances distribution,exchanging heat quantity distribution and the available work loss distribution.(3)We also used the experiment platform to study the steady state characteristics of the Hampson type heat exchanger,and the refrigerants are nitrogen and argon,respectively.The results show variation of the back pressure with different inlet pressure,variation of the back pressure with different fin spacing,variation of the operating temperature with different heat exchanger length,and variation of the operating temperature with different environmental pressure.Then,the measured data are replaced in the initial conditions of the numerical model,making the model more reliable.(4)We have a single factor optimization for the finned-tube heat exchanger,and in the case of nitrogen and argon,the change trend of the efficiency of heat exchanger and the ideal cooling capacity were analyzed with different mass flow rate.Besides,we also analyzed the influence of the heat exchanger length on the ideal cooling capacity.(5)Based on the steady-state numerical model of Hampson type J-T cryocooler,the proposed RSM is used to analyse the correlations between the geometry such as the tube diameter,fin height,fin spacing and axial length of heat exchanger,and their relationships to the response of the available work loss and the ideal cooling capacity.The structural parameters which minimize the loss of available energy and maximize the theoretical cooling capacity are obtained respectively.Besides,The genetic algorithm is used to optimize the available work loss and the ideal cooling capacity,with the same weight as 0.5.