An Optimization of the Principal Design Parameters of Stirling Cycle Machines

Abstract

A Stirling engine is a mechanism used to convert heat into power or vice versa and operates on a closed regenerative thermodynamic cycle with compression and expansion of the working fluid at different temperatures. According to the classical theory the performance of a Stirling cycle machine is a function of six independent parameters, namely: speed, pressure of the working fluid, ratio of the temperatures in the compression and expansion spaces, ratio of the swept volumes in these two spaces, phase angle by which volume variations in the expansion space lead these in the compression space, volume of the heat exchangers and regenerator. The four parameters (3)–(6) must be selected at the design stage of the machine. The paper describes the procedure and presents the results of computations carried out to establish the optimum combinations of these four parameters for maximum engine output for the machine acting as a prime mover, maximum heat lifted for the machine acting as a refrigerator, over a combined temperature range from 30 to 3000°K. The output of a Stirling cycle machine can be expressed in terms of non-dimensional power or heat lifted in several different ways. Four methods were studied in detail, the parameters optimized and design charts prepared. Wide variations in the optimum parameter combinations were obtained and a partial explanation of this phenomenon is offered. Pressure-volume diagrams for machines of the same size were prepared for the four different parameter combinations. Maximum output was obtained from the machine designed on a basis of limited maximum pressure and total swept volume. The two charts relating to the case for prime mover and refrigerator optimized with regard to the maximum cycle pressure and total swept volume are recommended for use in future design work.