Bubble dynamics and forced convection boiling heat transfer with low velocity

The velocity potentials of a sphere moving and/or growing in an inviscid liquid near a wall have been constructed. The dynamic force associated with the various motions of the sphere are obtained. For the case of a sphere touching a plane while moving parallel to it, the force coefficient is found to be 0.577771 which is more than 10% larger than the earlier estimate of 0.51435 by Miloh. Exact solutions of the dynamic force and the kinetic energy are obtained for a bubble growing on a wall.; Analyses are also given for the unbalanced molecular momentum force on a vapor bubble due to the nonuniform evaporation/condensation around the liquid-vapor interface.; Forced convection nucleate boiling experiments with two levels of subcooling and velocity (7.4 and 12.9{dollar}spcirc{dollar}C; 1.7 and 4.3 cm/s) at three surface orientations (vertical, horizontal up and horizontal down) are conducted with R-113 using both semi-transparent thin gold film and gold-coated copper flat heaters. The test conditions were accurately controlled throughout the experiments with an uncertainty of {dollar}pm{dollar}1% in velocity, {dollar}pm{dollar}0.172 kPa in pressure (corresponding to {dollar}pm{dollar}0.06{dollar}spcirc{dollar}C in saturation temperature), and {dollar}pm{dollar}0.06{dollar}spcirc{dollar}C in temperature.; Experimental results show that in the range of velocity and subcooling tested, bubble departures are dominated by buoyancy; for both copper and quartz heaters subcooling and velocity have no appreciable effect on the heat transfer from the horizontal up surface; copper heaters generally have lower surface superheat than the thin gold film heaters at a given level of heat flux; for copper heaters, the horizontal up surface has lower surface superheat than vertical surface; for the gold film heaters, heat transfer on vertical surfaces is enhanced by increasing the subcooling, is insensitive to increasing velocity when the subcooling is low, and is degraded when the subcooling is high; for both types of heaters, the horizontal downward facing surface has a very low level of heat flux compared to the horizontal up and vertical surface for the same surface superheat.