Thermo-acoustic waves near the liquid-vapor critical point : the sound of heat – Pierre Carlès

Date: Wed. November 14th, 2007, 12:30 pm-1:30 pm
Location: Rockefeller 221

A fluid near its liquid-vapor critical point exhibits puzzling heat transfer dynamics, as temperature relaxation becomes faster and faster near the critical point (an observation which contradicts the expected critical slowing down of diffusive processes). The reason behind this seemingly paradoxical behavior is a fourth mode of heat transfer named the Piston Effect, which results from a subtle coupling between local heat diffusion phenomena and long-scale acoustic propagation. So far, only the average effect of this acoustic propagation had been observed in experiments and modeled theoretically. Recently however, the Japanese team of Akira Onuki achieved a direct observation of the acoustic waves produced by a local and rapid input of heat in a near-critical fluid, thus pioneering the direct observation of near-critical thermo-acoustic waves. In this presentation, we will show how asymptotic methods applied to the heat and mass transfer equations near the critical point may lead to the construction of a precise model of these waves for an arbitrary set of experimental conditions. Direct comparisons with the experimental results of the Japanese team, showing excellent agreement, will illustrate how this class of models may be put to use in the interpretation of such experiments.