An investigation of film boiling heat transfer from an oscillating sphere



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An experimental investigation was made of the effects of oscillatory motion on the film boiling heat transfer from a sphere to a saturated fluid. A transient technique was used to calculate the heat transfer rate from a 3/4-inch silver plated, copper sphere. Tests were conducted in liquid nitrogen and Freon-11 at atmospheric pressure. The sphere was oscillated in a vertical direction at frequencies of zero to 14 Hz and at amplitude-to-diameter ratios of 1.33, 2.00, and 2.67. High-speed movies of the boiling process were studied to identify the vapor envelope motion during the tests. Results of the tests indicate that the oscillation of the heat transfer surface increases the heat transfer rate over that for natural convection film boiling. The high-speed movies show that the vapor envelope undergoes a transition from natural convection to a forced convection film boiling with increasing sphere midstroke velocity. The results were correlated based on an equation proposed by Rhea [5], and based on a modification of this equation by the author. For the results of this study, the latter correlation furnished better correlation.