Suppression of liquid surface instability induced by finite-amplitude oscillation in liquid piston Stirling engine

Abstract

This study addresses a problem introduced by finite-amplitude oscillations in a liquid piston thermoacoustic Stirling engine and proposes methods to overcome it. After the engine was operated by external heat, the liquid piston oscillated, keeping a flat surface when the amplitude was sufficiently low. However, it became unstable to cause ejection of droplets and formation of air bubbles because the acceleration amplitude exceeded gravitational acceleration. Two methods were proposed to recover the stable liquid surface: one method was the enlargement of the cross-sectional area of the tube around the liquid surface and the other method was the use of submerged polyethylene floats. These methods successfully suppressed the instability of the liquid piston Stirling engine and increased the pressure amplitude by almost twice of the original engine. In addition, adjusting the liquid filling level resulted in the ratio of pressure amplitude over the mean pressure reaching 18% when the acceleration amplitude was elevated to 36m/s2 by the installation of floats. The high-pressure amplitude is an advantage of a liquid piston thermoacoustic Stirling engine over thermoacoustic engines that use only gas as the working fluid.

Viability of low‐grade heat conversion using liquid piston Stirling engines

“…The regenerator had a 120-strand stainless-steel mesh with a porosity of about 73%. In an extension to this research (Murti et al, 2020), the surface of the liquid piston was observed to become unstable at higher oscillation amplitudes resulting in the formation of air bubbles. An enlargement of the tube cross-sectional area around the liquid and the usage of a submerged polyethylene float remedied this instability to further increase the pressure amplitude by a factor of two.…”

Design and construction of multi-cylinder type liquid piston Stirling engine

“…Two K-type thermocouples were placed at ends of the regenerators to measure the temperature T H and T C . A cylindrical rod of ultra-highmolecular-weight polyethylene with a diameter of 38 mm and a length of 300 mm was used as a float to suppress the liquid surface instability [9].…”

Multi-physics coupling in thermoacoustic devices: A review

“…Besides, for the travelling-wave liquid-piston TAE, the gas-liquid interface will become unstable when the acceleration amplitude of the working liquid is large. A recent study by Biwa [249] shows that the liquid surface instability can be effectively suppressed by enlarging the area of liquid surface or using submerged floats.…”