Industrial Research Ltd has developed a unique diaphragm-based pressure wave generator technology for employment in pulse tube and Stirling cryocoolers. The system uses a pair of metal diaphragms to separate the clean cryocooler gas circuit from a conventionally lubricated mechanical driver, thus producing a clean pressure wave with a long-life drive. The same diaphragm concept has been extended to support and seal the displacer in a free piston Stirling expander. Diaphragms allow displacer movement without rubbing or clearance gap seals, hence allowing the development of cost-effective, long-life and efficient Stirling cryocoolers. A proofof- concept prototype has achieved cryogenic temperatures.

The diaphragm’s large diameter and short stroke produces a significant radial component to the oscillating flow fields inside the cryocooler which are not modelled in one-dimensional analysis tools such as Sage. Compared with standard pistons, the gas-to-wall heat transfer is increased due to the higher velocities and smaller hydraulic diameters. This paper presents the results of Computational Fluid Dynamics (CFD) analysis used to model the flow and gas-to-wall heat transfer inside the cryocooler, including experimental validation of the CFD to produce a robust analysis.