Optimizing heat exchanger parameters of a joulethomson cryogenic cooler to improve the cooling performance

Baki, Murat
Cryocoolers are one of the key components of cooled infrared (IR) imaging systems, where it is not possible to form an image in photon detectors without decreasing the sensor temperature to cryogenic temperatures. In detector cooling applications where low cool down times, small size and weight are required, mostly Joule Thomson (JT) cryocoolers are preferred. The aim of this study is to analyze the heat exchanger of a JT cryocooler operating with argon as the working gas, numerically and optimize its design parameters. For this purpose, a numerical model is built to solve Navier-Stokes and heat transfer equations. Using the numerical model, an optimization study is applied using stochastic method to maximize the specific cooling power of the cryocooler and minimize the shell side pressure drop. The possible optimization parameters are determined as total length of the heat exchanger, capillary tube diameter, capillary tube wall thickness, fin density, fin thickness and fin length. The design parameters are varied within certain limits. A result cloud is obtained using full factorial method. The two contradicting objectives are brought together by weighted averages approach and an optimization function is formed. The optimum geometry which maximizes the optimization function is searched using grid search method. Finally, a second iteration of the optimization is performed by using the optimum geometry obtained from the first iteration. An optimum geometry is obtained, where flow rate is decreased by 46%, which results in an increase of the operation time, and the shell side pressure drop is decreased by 90%, which results in a decrease of the target body working temperature.


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Citation Formats
M. Baki, “Optimizing heat exchanger parameters of a joulethomson cryogenic cooler to improve the cooling performance,” Ph.D. - Doctoral Program, Middle East Technical University, 2018.