CFD Analysis of a Pulse Tube Cryocooler

Abstract

Pulse tube refrigerators are latest technical instrument in the field of refrigeration engineering. So they are preferred over other types of cryocooler like Stirling and Gifford-McMahon coolers because of no moving parts in the cooler making the cooler widely useful for various purposes. Other ordinary refrigerators use vapor compression cycle but pulse tube utilizes oscillatory expansion and compression of gas present inside it. Pulse tube cryocooler has long life compared to other refrigerators, high reliability and low vibration because of no solid piston moving. These coolers have vast applications like semiconductor manufacture and its endless use in military for the cooling of the infrared sensors. They are also used for the cooling of astronomical detectors. They are also used for pre coolers of dilution refrigerators. They are used in space application also. In this work study of Stirling type OPT cryocooler is considered for CFD analysis using fluent present in ANSYS15 workbench. 2D axis-symmetric geometry is created and used for CFD analysis. The simulations represent a fully-coupled system operating in steady periodic mode, with a trapezoidal pressure profile. Nothing is assumed rather than ideal gas and no gravity effect. The boundary conditions applied on this model are a oscillating pressure of trapezoid profile created using user defined function (UDF), thermal boundary conditions like adiabatic and known heat flux at the cold end heat exchanger. The purpose is to study the Orifice Pulse tube cryocooler(OPTR) using CFD fluent analysis. Where dimensions of components of OPTR are taken from YP Banjare thesis[1] for values of optimum result. In order to observe refrigeration pressure wave of same specification like frequency and amplitude are applied for both cases as described. For each condition two separate analyses are done. One analysis assumes no load or adiabatic cold-end heat exchanger (CHX); other assumes isothermal or known cooling heat load. Each analysis was started with initial conditions, and carried on until steady periodic conditions are attained. The unsteady CFD model successfully predicts OPTR performance through solving an ideal gas equation and heat transfer. The result is discussed in Result and Discussion section.