Abrupt reduction of the critical temperature difference of a thermoacoustic engine by adding water

The critical temperature difference (ΔTcri) that causes a thermoacoustic spontaneous oscillation is reduced by the presence of water in the working fluid of a thermoacoustic engine. This letter introduces the effects of two design parameters on the reduction of ΔTcri: one is the mass of water added as the working fluid and the other is the characteristic length of the stack, which is the heart of a thermoacoustic engine. The experimental results show that when the mass of added water exceeds the threshold value, ΔTcri decreases abruptly; however, the decreased ΔTcri changes slightly with further increase in the added mass. Moreover, the characteristic length of the stack was found to have little effect on ΔTcri when water is added. These results provide a design guide for a thermoacoustic engine that includes water as the working fluid.