Measured Temperature Profiles Within the Superheated Boundary Layer Above a Horizontal Surface in Saturated Nucleate Pool Boiling of Water

Abstract

Temperature measurements were made within the superheated boundary layer above and adjacent to a horizontal heating surface in saturated, nucleate, pool boiling of water. A microthermocouple probe was used to measure the average temperature profiles and the temperature fluctuations within the boundary layer at heat fluxes from 1000 to 40,000 Btu/hr-sq ft. Correlations are presented for the “extrapolated” thickness of the boundary layer (δ) as well as the temperature distribution within it. It was found that the thickness (δ) could be expressed in terms of the heat-transfer coefficient as: δ = Chd. Also, the behavior of δ with system parameters was found to agree with that predicted by Han and Griffith [3] and Hsu [4] in their theories of nucleation from surface cavities. The temperature distribution in the boundary layer from the surface to 0.57δ was essentially linear and could be expressed: (T − Tb)/(Ts − Tb) = 1 − (y/δ). Above 0.57δ the temperature profile became an inverse power function of the height above the surface: (T − Tb)/(Ts − Tb) = D(y/δ)−a.