ISSN Online: 2377-424X
ISBN Print: 978-1-56700-474-8
ISBN Online: 978-1-56700-473-1
International Heat Transfer Conference 16
ACOUSTIC HEATING AND BUOYANCY-DRIVEN INSTABILITY INDUCED BY MASS TRANSPORT IN A NEAR-CRITICAL BINARY FLUID MIXTURE
Abstract
Approaching the liquid-vapor critical point, strong anomalies in thermodynamic and transport properties induce a fast heat transfer mechanism called the piston effect. In this study, we identify a piston-effect-like phenomenon and the ensuing buoyancy-driven instability in a Rayleigh-Bnard-like problem: a near-critical dilute binary fluid mixture confined in a rectangular cavity submitted to concentration increase at the bottom in the presence of gravity. The results were obtained by numerical simulations. They show that after the concentration increase, a thin diffusive layer with both concentration and temperature gradients forms and expands due to the diverging expansion coefficients and the vanishing diffusivities, causing a homogeneous acoustic heating in bulk fluid. The progressively growing boundary layer leads to the onset of convection, which improves the mass transfer in the whole domain than a purely diffusive way. The evolution of velocity field in a long time is described, with an emphasis on the abnormal velocity fluctuations caused by the strong coupling between concentration and density during the early stage of convection.