Dissipation-induced chemical potential gradient and limiting velocity in thermally drivenHe4film flow

Abstract

We have measured the local film thickness, temperature, and flow velocity of a ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ film on both sides of a dissipation region with the use of third-sound techniques. All of these parameters are observed to saturate when a critical heat current is reached which leads to an unavoidable limiting velocity whenever the film is thermally driven. The observed chemical potential drop across the dissipation region suggests the vapor maintains equilibrium with the film in the regions of subcritical flow and that dissipation primarily produces a change in film thickness.