INFLUENCE OF PRESSURE ON FILM BOILING HEAT TRANSFER.

Experiments on film boiling of carbon dioxide were performed covering the range of pressures from the triple point to the critical point. Measurements were also made at supercritical pressures. Three different heating wire sizes were employed with diameters of 0. 0508, 0. 1, and 0. 4 mm. The boiling curves, plotted in terms of heat flux and temperature difference, are found to be pressure dependent, with a more marked dependence for smaller diameter heating wires. The role of pressure level is exhibited in greater detail in a presentation in which the heat transfer coefficient is plotted against pressure at fixed values of heat flux. The most rapid variations of the heat transfer coefficient with pressure occur in the neighborhoods of the triple and critical points, with relatively gradual variations in evidence in the intermediate range of pressures. Nusselt numbers evaluated from the experimental data agree satisfactorily with available predictive equations.