Interaction of Acoustic and Thermal Modes in the Vibrationally Relaxing Gases. Acoustic Cooling

The dynamic equation which governs an excess temperature associated with the thermal mode in vibrationally relaxing gas is derived. The nonlinear transfer of acoustic energy to the energy of the thermal mode in a relaxing gas causes slow variation of temperature with time. The final dynamic equation is instantaneous. All types of sound, including aperiodic, may be considered as an acoustic source of corresponding heating or cooling. The study considers sound with frequencies much larger than the inverse time of the thermodynamic relaxation. In the nonequilibrium regime, if standard attenuation is neglected, gas temperature decreases with time. Examples concern heating and cooling caused by periodic in time sound and an impulse. The influence of standard viscosity, thermal conductivity, and heat withdrawal is briefly discussed.