Novel Twin-Screw Stirling Cycle Machine for Cryogenic and Refrigeration Applications

This paper describes design and principles of operation of a novel rotary type Stirling cycle machines based on rotary positive displacement mechanisms such as twin-screw, gate rotor screw, scroll, and conical screw compressors and expanders. When these mechanisms are used as separate expanding or compressing machines, the flow of the gas is one-directional with volumes of chambers varying in accordance with a saw-tooth type function. The proposed design solution combines at least two units of gas-coupled compressor and expander arrangements with a required shift in the shaft angle. Every unit has a series of gas channels for timing the connection of its compressor and expander parts. Units are connected to each other via a set of heat exchangers, which are conventional for Stirling cycle machines: recuperative cooling and warm heat exchangers with a regenerator, built between them. The operational capability is demonstrated using three-dimensional CFD simulations. Computational results demonstrate reciprocating flow of the gas between units, as in conventional Stirling machines, and functioning of the proposed design as a multi-cylinder, double acting Stirling machine. The suggested design makes it possible to achieve full dynamic balancing, especially in the case of twin-screw and gate rotor mechanisms, due to the rotation of screws around their axes. It also eliminates a number of problems, which are specific to Stirling machines with reciprocating pistons and their kinematic drive mechanisms.