Downflow Post-Critical Heat Flux Heat Transfer to Low Pressure Water

Post-critical heat flux heat transfer data for water in downflow have been obtained for the following conditions: mass velocity, 48.8 to 147 kg/s·m²; wall temperature, 538 to 760°C; pressure, 1.3 to 2.6 bars; quality, 4.1 to +5.8%; tube diameter, 1.25 cm; and tube length, 66 cm. At low mass velocity, a frozen equilibrium model predicts the data well. At high mass velocity, droplet-vapor heat transfer is good enough so that a homogeneous equilibrium model predicts the data. Under no circumstances is droplet-wall heat transfer significant. When the vapor is in laminar flow, the heat transfer is particularly poor and the radiant heat transfer becomes a significant fraction of the total.