Analysis of thermal processes in a liquid piston Stirling engine

Application of the thermodynamic principles of Stirling engine for the power industry can give a large capability to increase the energy conversion efficiency. However, it is not possible yet to produce large-scale power facilities competitive with conventional ones on the base of existing technological implementations of Stirling engine principles. The reason is high costs of Stirling engines caused by numerous difficulties in operation with high pressure and volatile working gas that is typically helium or hydrogen. The liquid piston engine can be an alternative approach in that many problems inherent to a conventional Stirling engine can be eliminated. The analysis of studies of liquid piston Stirling engines has shown that one of the most attractive direction of this technology development is associated with the use of liquid metals with low melting temperature (particularly, Na-K eutectic) as the both working liquid and heat carrier. A liquid piston Stirling engine is remarkable for the following features. The first is an opportunity of supplying heat to a working gas during expansion process and rejecting it during compression processes by means of a liquid heat carrier. The second feature is larger, as compared with the conventional Stirling engine, opportunity of controlling the operation regime by setting a consequence of expansion and compression processes in working cavities. These features are analyzed in the present study with respect to possibility of increase of engine effi ciency. The analysis is carried out on the base of numerical simulation of gas dynamics and heat exchange in working cavities and regenerative heat exchanger of a Stirling engine. Optimization simulation is carried out for the purpose of finding out the optimum time dependency of working cavities volumes that may be realized in a liquid piston engine. It is shown that organization of heat exchange between a working gas and liquid heat carriers within hot and cold cavities of engine can result in a significant growth of the engine thermodynamic efficiency. The obtained estimations count in favor of that the liquid piston Stirling engine can be an effective and competitive power facility.