Isothermal Model of a Warm Expander Pulse Tube

Abstract

This paper describes a numerical model of a novel type of cryocooler for long life applications, the Warm Expander Pulse Tube (WEPT). The model was used as a design tool for the initial sizing of a breadboard miniature cooler.

The model is of the second order, based on an isothermal analysis with losses considered separately. Although it is more complex than the isothermal model of a Stirling refrigerator, it is much simpler than a full nodal analysis.

The model shows that the power dissipated at the warm end of the pulse tube via the warm expander is equal to the gross heat lift. In principle this power may be partially recovered as electrical energy. The action of the warm expander also produces a high pressure ratio, which enables a miniature machine to maintain a relatively high work rate.

An expression is developed for the cyclic pressure drop in the regenerator. This incorporates empirically determined parameters of the regenerator matrix to predict both pressure drop and phase shift. Thermal conduction measurements of the regenerator matrix under different loading conditions are also incorporated into the model.

The model demonstrates that the WEPT can achieve an overall efficiency comparable to or exceeding that of the Stirling cycle refrigerator, with the advantages of no moving components at cryogenic temperatures and the elimination of shuttle heat transfer.