Instantaneous Heating and Cooling Caused by Periodic or Aperiodic Sound of Any Characteristic Duration in a Gas with Vibrational Relaxation

Thermodynamic relaxation of internal degrees of a molecule's freedom in a gas occurs with some characteristic time. This makes wave processes in a gas behave differently depending on the ratio of characteristic duration of perturbations and the relaxation time. In particular, generation of the secondary non-wave modes by intense sound in a nonlinear flow dependens on frequency. These kinds of interaction are considered in this study. The exact links between perturbations inside every type of a fluid's motion (modes) and resulting weakly nonlinear equations for interacting modes are derived. These equations are instantaneous and hence are valid for pulsed excitation. Some kind of energy inflow makes a gas with excited degrees of oscillatory molecule's freedom acoustically active. That leads to anomalous acoustic cooling of a gas. The impact of standard viscosity, thermal conductivity, and dependence of the power of energy inflow on temperature is briefly discussed.