Working gases in thermoacoustic engines

The best working gases for thermoacoustic refrigeration have high ratios of specific heats and low Prandtl numbers. These properties can be optimized by the use of a mixture of light and heavy noble gases. In this paper it is shown that light noble gas-heavy polyatomic gas mixtures can result in use ful working gases. In addition, it is demonstrated that the onset temperatu re of a heat driven prime mover can be minimized with a gas with large Pran dtl number and small ratio of specific heats. The gas properties must be op timized for the particular application of thermoacoustics; it cannot be ass umed that high specific heat ratio and low Prandtl number are always desira ble. (C) 1999 Acoustical Society of America. [S0001-4966(99)04205-8].