ADIABATIC TEMPERATURE-CHANGES IN A ONE-COMPONENT FLUID NEAR THE LIQUID-VAPOR CRITICAL-POINT

The theory of the fast adiabatic equilibration that results from the diverging thermal-expansion coefficient is extended to take into account the finite thermal conductivity of the container walls. As the critical point is approached and the fluid thermal impedance drops below that of the walls, a crossover takes place to a new regime in which the equilibration time varies as the square of the constant-volume specific heat. We also study the adiabatic changes that are generated by an internal heat pulse and by pressure modulation. The latter technique should make light-scattering experiments feasible very close to the critical point by avoiding the strong density stratification that sets in at thermal equilibrium. In the concluding portion of the paper, we propose experimental tests of the theory by interferometry and by sonic attenuation and dispersion.