Oscillating flow in a stirling engine heat exchanger

Three heat exchangers exist in modern Stirling engines: a heater, a cooler, and a regenerator. Here a study that deals principally with tubular heaters and coolers is carried out. The calculation procedure for the oscillating flow heat transfer is presented. Literature sources are studied to find the most suitable correlations by comparing them to each other and to the classical turbulent flow correlations encountered in the literature. The enhancement of heat transfer by means of a few circumferential slots inside the tubes and the pressure losses of oscillatory flow are discussed. Non-circular cross-section conduits with rectangular and triangular cross-sections are investigated and compared to the smooth circular tubes. The increment of the performance of an idealised Stirling engine with slotted heat exchanger tubes is compared to the case with smooth ones. The ratio of the gain in the shaft power and pumping losses is 2.22. The Carnot efficiency increment is 2.7%.

► Hydrodynamics and dimensionless numbers of oscillating tube flow derived from piston motion.
► Rectangular, triangular and circular tubes with inside slots studied.
► Heat transfer and pressure equations compared to enhance Stirling engine performance.