(Dr. Prateen V. Desai, advisor)
"Oscillatory Compressible Flow and Heat Transfer in Porous Media: Application to Cryocooler Regenerators"
Regenerative refrigerators and engines all rely on the reciprocating flow of a working fluid through an optimally designed regenerator. The flow and heat transfer processes in the regenerator are complicated by the fact that the flow passages are irregular and the path is tortuous. To develop a mathematical model for the regenerator, the method of volume averaging was applied to the governing equations. The resulting equations are a set of hyperbolic partial differential equations (PDEs) which are then solved numerically using the Method of Lines (MOL.) The uniqueness of this model lies in the fact that the system of equations are all solved implicitly, requiring the pressure gradients to be not neglected in the momentum and gas energy equations. In addition, the boundary conditions are less restrictive in the sense that the velocity is not imposed on the ends.
An experimental apparatus has been designed and instrumented to validate the results of this model. The apparatus utilizes a Orifice Pulse Tube Cryocooler (OPTC) which is based on simplified Stirling refrigerator design. The expansion process is accomplished using an RLC-type fluidic design known as the pulse tube. Experiments have been performed to document the variation in performance and operating conditions for several different regenerator geometries but with identical material properties. These measurements and accompanying simulations aim to demonstrate the usefulness of the model. Further measurements and simulations will aim to expand the range of usefulness for the model under a variation of geometry and possibly materials.