The visualization study of Rayleigh-Bénard convection in supercritical CO₂ is conducted by both interferometer measurements and numerical calculations to investigate the heat transfer and flow instability behavior induced by the high compressibility and large density variations in fluids. The process is studied in the vicinity of the critical point and the Widom line of CO₂. The results found a large amount of the plume flow with small-scale circulation flow emerges when the onset of the convection in the length scale of 10^-2 m, which leads to the heat transfer heterogeneity with Nusselt number variation up to 3×10⁴. Such heterogeneity is enhanced when the compressibility is large while the dissipation is weak.
 

Heat transfer, Rayleigh-Bénard convection, Supercritical fluids, Visualization