ADIABATIC HEATING EFFECT NEAR THE GAS-LIQUID CRITICAL-POINT

A new feature of macroscopic thermal relaxation processes is investigated in pure fluids near the gas-liquid critical point. If the total volume of the fluid is fixed, an adiabatic heating process can be the dominant temperature equilibration mechanism near criticality. That is, if the boundary temperature is changed, the resultant boundary diffusion layer acts as an efficient piston instantaneously producing an adiabatic volume change in the interior region. As a result, inhomogeneities of the fluid temperature are greatly reduced on a time scale rapidly going to zero at the critical point. On the other hand, when the two phases coexist below Tc, the adiabatic process induces a flow of latent heat through the interface. This flow persists for a long time and slows down the equilibration. © 1990.