Decoupled duplex Stirling machine: Conceptual design and theoretical analysis

In this paper, a conceptual design of decoupled duplex Stirling machine was described. The motions of the displacers and the shared piston were decoupled by controlling the displacers and piston to be stationary at the top or bottom dead center. The overall coefficient of performance (COPoverall) of decoupled duplex Stirling machine could achieve 1.11-1.4 and 1.7-2.1 for cooling and heating respectively. In order to meet the constraint of work equality of engine and cooler at the off-design conditions, two methods of decreasing the hot temperature and increasing the dead volume were employed in the engine for adjusting engine's generated work. The COPoverall could be decreased by up to 19.4% at the off-design conditions due to the reduction of engine's thermal efficiency as a result of decreasing the hot temperature or increasing the dead volume. Furthermore, increasing dead volume could have a up to 18.6% improvement of COPoverall compared to reducing the hot temperature. Moreover, an isothermal heat exchanger was also designed for improving the COPoverall. If the additional average pressure drop of each isothermal heat exchanger was lower than 30 kPa, the COP improvement of cooler could be 10% for heating and cooling.