טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentWeissman Narda
SubjectStudy of Regenerators for Stirling Cryogenic Cooler
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Emeritus Gershon Grossman


Abstract

By definition a regenerator is a cyclic device. On the first part of the cycle the hot gas flows through the regenerator, and in so doing transfers heat to the regenerator matrix.  Subsequently during the second part of the cycle the cold gas flows in the reverse direction, absorbing the heat that was previously stored in the matrix.  These heat exchangers are an integral part of the Stirling refrigeration cycle.

The regenerator efficiency has a significant influence on the overall efficiency of the Stirling refrigerator.  The regenerator has not been adequately investigated.  Until recently all the regenerator studies incorporated flow correlations corresponding to steady state flow and did not take into account the effects of the oscillating flow. 

In order to further improve the Stirling refrigerator, a tool has been developed which investigates the influence of various parameters on the overall performance of the regenerator while including the effects of the oscillating flow.  The model, proposed in this work, is made up of equal two dimensional plates which are spaced one from another. In the space, between the plates, is where the oscillating gas flows.  The flow velocity is induced by applying an oscillating, sinusoidal pressure along the axis.  The flow profiles are obtained from the solution of the continuity equations and the Navier-Stokes equations.

The temperature field was obtained by solving the energy equations in the solid and fluid.  The velocity and the temperature are taken to be two dimensional.

The temperature, velocity and the heat flux profiles as a function of time and cross section have been calculated. The resulting velocity, temperature, and heat flux all have the same frequency but are phase shifted with respect to the driving pressure.  This work determines the heat transfer at the interface, the average cross section temperature and heat transfer coefficients.  The detrimental axial heat convection resulting from the oscillating flow was also examined.  The gas dissipation is calculated as well as the overall regenerator effectiveness.  

This work has resulted in a mathematical tool, which is useful in examining regenerator performances. This tool allows a parametric investigation of any regenerator. Additionally, the change in different parameters will also allow a comparison between various types of regenerators.