(85e) Numerical Simulation of Heat Transfer and Oscillating Fluid Flow In a Cryogenic System with Pulse Tubes

In recent years, understanding of oscillating flow and energy transfer in pulse tube refrigerators has been a subject of great interest. Despite considerable research over the past many years, comprehensive numerical simulations of the transport processes in a complete cryogenic system involving a pulse tube, the heat exchangers, and other elements are still lacking. A comprehensive numerical simulator has been developed to study this problem and the detailed thermodynamic performance of the system as a function of heat exchanger size and performance. The simulator solves the appropriate energy and momentum equations for a compressible fluid in oscillating and reversible flows, using the method of finite volumes. Theboundary conditions are not applied using numerical function, but rather, a novel approach that involves dynamically modifying boundary surfaces to create the necesary pressure gradients, while the oscillations are used simulate the actual pulse tube flows. The effects of the applied pressure gradient, inertia, and viscous terms are all taken into account in solving this problem. The effects of the fluid properties, the tube's geometry, and the macroscopic (measurable) parameters of the system on the energy transfer process are examined, as is the effect of conduction through pulse tube's wall on the net diffusion into and out of the Stokes' layer. Both the amplitude and phase of the displacement profile are determined as functions of the tube's aspect ratio.