Free-Convective Heat Transfer to a Supercritical Fluid

The influence of heater material on free-convective heat transfer from wires to carbon dioxide in the supercritical region was investigated. Three types of flow configuration were observed for nichrome and alumel wires: (a) conventional laminar-flow free convection, (b) an oscillating flow in which (a) and a bubble-like flow alternated, (c) a bubble-like flow in which masses of fluid similar to bubbles appeared successively near the heating surface. Neither (b) nor (c) was observed with a platinum wire. The heat-transfer rate increased suddenly when the flow configuration changed from (a) to (b). The transition in flow structure occurred when the temperature difference between the heater and fluid exceeded about 200 deg C.