NEAR-ISOTHERMAL REGENERATOR - A PERTURBATION ANALYSIS

We develop a perturbation model for regenerators of the type used in S tirling and Gifford-McMahon cryocoolers. The model is valid in the nea r-isothermal limit, which is usually a quite good approximation for th ese devices, because typically, the flow passages are small compared t o the conductive heat penetration depth in the gas, and because the th ermal mass of the heat-storing matrix is large compared to the thermal mass of the gas. Our model is one dimensional and it uses a conventio nal, empirical model for heat transfer. Our approach can yield solutio ns for arbitrary heat transfer correlations, which makes it suitable f or incorporation in computer models. We also present complete solution s for the important case corresponding to the laminar limit, when the Nusselt number is a constant. Results include the longitudinal tempera ture distribution and the enthalpy nux through the regenerator. In som e conditions, which are more representative of pulse-tube refrigerator s than of typical Stirling cryocooler operation, and for which the mod el remains valid, we obtain multiple solutions, some of which are asso ciated with a sharp temperature peak, in a region in the regenerator w here the amplitude of the mass flow rate oscillation exhibits a minimu m.