טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentFraiman Leonid
SubjectHeat Transfer Enhancement in Counter-Flow-heat-Exchanger
for Use in Micro-Fabricated Joule-Thomson
Cryocooler
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Gilad Yossifon
Full Thesis textFull thesis text - English Version


Abstract

IR imaging systems require a low cost, small scale and reliable cooling device for maintaining a cryogenic temperature on the detector matrix, for achieving valuable image quality. Joule-Thomson (JT) cryo-cooler is a well-known device, designed to achieve coolant liquefaction at a constant cryogenic temperature at its cold tip. In the current work, we studied the performance of microscale JT cooler with integrated microscale counter-flow heat-exchanger (µCFHE) having an array of structural pins and operating using nitrogen gas. Scaling effects, associated with micro-scale flow and heat transfer, were examined and properly treated. The geometry of the µCFHE and mass flow rate were optimized to produce the maximum cooling power under the limitation of device inner pressure drop for achieving coolant liquefaction conditions. The optimization procedure consisted first on an approximate solution using the NTU method with experimentally derived correlations for the convective heat transfer coefficients obtained from the literature. Then, the optimization results were supported by computational fluid dynamics (CFD) analysis performed using ANSYS Fluent software. The proposed device prototype was built from three layers of glass slides using photolithographic micromachining process incorporating wet etching process, followed by glass-glass specially adapted thermal bonding procedure. The performance of such glass made cooler were investigated using a specially designed experimental setup and compared against both approximate solution and numerical simulation data, and were found to be in good agreement. Thus, validating the proposed generic optimization technique which can be applied for various microscale heat-exchanger designs