STUDY OF COOLING CHARACTERISTICS OF INFRARED DETECTOR CRYOCHAMBER

Abstract

The present work, along with the study of design considerations of an Infrared detector cryochamber investigates the steady and transient cooling characteristics of an Infrared detector cryochamber for various operating conditions. The design aspects of a cryochamber housing the device for achieving its have also been studied. The major considerations as far as design of cryochamber is concerned are; choice of material of the cryochamber, manner of electrical feedthrough, vacuum sealing and type of cryocooler. These few prime areas concerns which influence the performance of the devices sealed in these cryochambers. The thermal model developed considers the conduction heat transfer through a cold well, the gaseous conduction due to outgassing, and the radiation heat transfer. The thermal modeling of the cryochamber has been carried out for both steady state as well as transient conditions using a finite volume method. The basic algorithms for solution of steady state and transient state cryochamber heat transfer problem were developed and the numerical codes for both the cases were written in MATLAB. In case of steady state analysis it is found that the length profile of temperature is linear owing to conduction at negligible gas conduction. However, as the influence of gas conduction increases it greatly affects the length temperature profile. In case of transient flow, the cooling down time is mostly affected by the bore conductivity and gas conduction coefficient seems to have little influence. The efficacy of the numerical models has been established by performing detailed experimental studies and also by comparing with existing data. The code enables prediction of transient cooling performance of the cryochamber under various conditions viz., “no bias” and “with bias” condition, variation in ambient temperature, variation in cryochamber vacuum and its influence on gas conduction coefficient The computer program developed allows the determination of cooling characteristics specially the cool down time of cryochambers of varying materials and dimensional configurations with differing material and transport properties.