Thermodynamic Optimization of Multi-Stage Cryocoolers

Abstract

Active Stirling class cryocoolers, including pulse tube coolers, are complex, difficult to optimize machines. The large number of characteristics and properties associated with geometry, materials, gas properties, heat transfer devices, flow manifolds, mechanical mechanisms, and electro-mechanical devices that determine a particular machine’s performance make quick optimization difficult. Single-stage coolers are now sufficiently well understood that design optimization is reasonably straight forward. However, multi-stage coolers compound the design problem by virtue of the dramatically enlarged number of variables, and optimization is still a challenge. Often, multi-stage machines are “optimized” by a brute force search of the design space or design decisions are made based on overly generalized or inaccurate assumptions about relationships between variables. The schedule-constrained time typically available to perform optimization procedures combined with the large number of variables and their complex interaction results in sub-optimal products. This paper presents a concept for optimization that more rapidly converges on an optimal design.