Natural convection in phase change material: Experimental study

Natural convection in a melting material (hexadecane) is studied experimentally using Magnetic Resonance Imaging. This imaging technique allows to discriminate solid and liquid phases measure velocity vectors the volume sample, even through/in opaque phases. Within our experimental conditions, occurs above Ra≈1430. The thermo-convective flow affects interface leading higher height uprising lower downward regions. Our experiments show that (i) transient evolution of mean h¯ enhanced with since h¯∝t0.8 (h¯∝t12−3β β=1/4), while h¯∝t0.5 conductive regime similarly Stefan’s problem; (ii) steady averaged increases 4 times larger convective than regime. In range A, ratio between heights, such as A>1.5. this values we obtain pattern under form hexagons / polygons. As boundary grows, observe decrease polygon number. polygonal characterized by constant dimensionless wavelength, i.e. λ/h¯≈2, thus wavenumber around 3.1 primary bifurcation classical Rayleigh–Bénard Convection (RBC). Heat transfer evaluated via Nusselt number Nu. Close onset above, results highlight scaling law Nu∝Raβ β=1/4 RBC. kinetic energy Ec also measurements Ec/E0∝Nu4 therefore Re∝Ra2β∝Ra1/2. frame experiments, all laws are converging β=1/4. They reflect clearly an increase intensity from both thermal dynamical points view.