The Thermodynamics of Stirling Engines Revisited: The Relative Merits of Hot Zone or Cold Zone Work Extraction

It was demonstrated by analytical means, that the specific work obtainable from a Stirling type engine, with separate power and displacer cylinders, having the power cylinder connected to the hot zone of the displacer cylinder is, for typical operating conditions, about twice that obtainable when the power cylinder is connected to the cold zone. The analysis, which does not reveal any differences in ideal thermal efficiency between cold-zone and hot-zone power cylinder connections, is based on conventional thermodynamic concepts applied in a manner which differentiates explicitly between the conditions applicable to hot-zone versus cold-zone interconnection of the power and displacer cylinders. A new feature of the analysis is the introduction of what have been termed bithermal processes. These involve two regions of different, but constant, temperatures with mass exchange between the regions which communicate freely via the engine regenerator. At any instant the pressure is equal in the communicating regions of a bithermal process.