Parametric analysis of the thermal components of an alpha-stirling engine for cogeneration applications

Abstract

Stirling engines efficiency, the increased maintenance interval periods, the variety of energy sources and the relatively low gas emissions makes Stirling technology an interesting choice as prime mover for cogeneration applications. These are some of the reasons that justify the attention received from researchers in the last years, focused in its modelling, optimization and its application in the suppression of buildings energy needs. In this study, an alpha-Stirling engine was numerically modelled. At this configuration, the working fluid flows between expansion and compression spaces by alternate crossing of, a high temperature heat exchanger (heater), a regenerator and a low temperature heat exchanger (cooler). Thus, the engine is considered as a set of five components connected in series. MatLab® environment was used to implement a software-code to model the thermodynamic cycle of the Stirling engine. The modular code allows investigating the influence of different geometrical and thermal parameters of all the engine components that affects its power production and the efficiency, the effectiveness of heat exchangers and the design itself of the power plant. This parametric analysis helps finding some restriction values for geometrical parameters that cannot be solved through the optimization procedures. For instance, at some point, there is a geometrical limit for which the increase in heat transfer is overlapped by the void volume or pumping losses increase. The parametric analysis led to an enhanced configuration of the numerical model, which resulted in the increase of engine thermal efficiency (about 13.4%), with a power production close to 5 kW.