Modeling and optimization of a combined cycle Stirling-ORC system and design of an integrated microchannel Stirling heat rejector

The performance of a combined Stirling-ORC power cycle is evaluated, and an integrated microchannel heat exchanger is designed as an annular cold-side heat rejector for a free piston Stirling engine. Reasonable designs for a combined cycle can increased power output efficiency by 3 - 9% compared to that of a Stirling cycle alone. This gives total power efficiencies near 34 - 40%. The study finds that power output may be optimized with an ORC expanding R245fa from saturated vapor. For such a system operating at maximum power, there are only small increases in power from a Rankine recuperator. Microchannel heat exchanger configurations with small pressure drop were found to increase heat transfer surface area and thermal conductance, though these required increased dead volume compared to conventional designs.