Stirling engine regenerators: How to attain over 95% regenerator effectiveness with sub-regenerators and thermal mass ratios

A combined theoretical and experimental approach is used to determine how to achieve a desired value for the Stirling engine regenerator effectiveness. A discrete one-dimensional heat transfer model is developed to determine which parameters influence the effectiveness of Stirling engine regenerators and quantify how they influence it. The regenerator thermal mass ratio and number of sub-regenerators were found to be the two parameters that influence the regenerator effectiveness, and the use of multiple sub-regenerators is shown to produce a linear temperature distribution within a regenerator, which enables the effectiveness to be increased above 50%. It is shown that increasing the regenerator thermal mass ratio and number of sub-regenerators results in an increase in regenerator effectiveness and a corresponding increase in the Stirling engine efficiency. A minimum of 19 sub-regenerators are required to attain a regenerator effectiveness of 95%. Experiments validated the heat transfer model, and demonstrated that stacking sub-regenerators, such as wire meshes, provides sufficient thermal resistance to generate a temperature distribution throughout the regenerator. This is the first study to determine how Stirling engine designers can attain a desired value for the regenerator effectiveness and/or a desired value for the Stirling engine efficiency by selecting appropriate values of regenerator thermal mass ratio and number of sub-regenerators.