Thermal Convection of a Phase-Changing Fluid

Abstract

To investigate the effect of phase transitions of the fluid on thermal convection, we are conducting experiments of thermal convection of the mixture of a thermosensitive gel and water. The gel absorbs water and swells below a certain critical temperature, while it discharges water and contracts above the critical temperature. The swelling ratio, as well as the critical temperature, can be controlled, which enables us to investigate the effect of phase transition in a series of experiments, where the critical temperature is set between the top and bottom boundary temperatures and the swelling ratio is systematically changed. In flow visualization, we have observed temporally stable and spatially fixed low-velocity regions which are surrounded by distinct high-velocity regions. Such a phenomenon is not observed in thermal convection of a single-phase fluid like water or air, and peculiar to the phase-changing fluid. Also, we have measured the rheological properties of the fluid and found, for example, the shear-thinning behavior, with which we try to explain the observed convection behaviors.