Effects of surface orientation on the pool boiling heat transfer in water/2-propanol mixtures

To explore the role of Marangoni effects in the pool boiling heat transfer of binary mixtures, experiments have been conducted with water/2-propanol m ixtures at three different concentrations under normal gravity with differe nt or orientations of the heater surface. The system pressure was subatmosp heric (similar to 5.5 kPa) and the bulk liquid temperature was near the sat uration temperature of the fluids tested The molar concentrations of 2-prop anol tested were 0.015, 0.025, and 0.1. These concentrations of 2-propanol are selected because their strong variation of surface tension with concent ration gives rise to high surface tension gl gradients near the heater surf ace during nucleate boiling. Boiling curves, were obtained both for all upw ard-facing and a downward-facing heater surface. For each concentration of 2-propanol, the critical heat has been reached in both orientations of the heater surface. Models of pool boiling heat transfer and the critical heat flux condition for binary mixtures are tested to correlate the data. Compar ison of boiling curves and CHF obtained at different orientations of the he ater surface indicates that there is strong gravity independent mechanism o f boiling heat transfer irt these mixtures.