Keywords: thermo-mechanical dissipation, irreversibility, exergy, plane shockwaves, mechanical dissipation, inviscid perfect gas
Mechanical dissipation versus thermo-mechanical exergy destruction for plane shockwaves in an inviscid perfect gas
In this paper, the physical exergy destruction caused by a shockwave, as an overall measure of the thermo-mechanical dissipation, is compared to the evaluation of mechanical dissipation alone. Travelling and stationary compression shockwaves are considered assuming an inviscid perfect gas with constant specific heats. Although quantities such as the change in exergy are not frame-indifferent, it is shown that mechanical dissipation and exergy destruction are both frame-indifferent. The results of this work reveal that, in many cases, the exergy destruction rate is a small fraction of the mechanical energy dissipation rate typically used to determine losses in gas dynamics. This is particularly true when the initial temperature of the fluid is high relative to the environment temperature. In contrast, the results show that, for very low initial temperatures that are below the environment temperature, the thermo-mechanical dissipation rate can be much greater than mechanical dissipation rate.