Photographic Study of Saturated Free Convection Stable Film Boiling

概要

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Experiments were carried out on the saturated film boiling of water and sodium oleate solution, using three kinds of nichrome wire, 0.6,0.8 and 1.0 mm in diameter and platinum wire, 0.5 mm in diameter. The bubble dynamics in stable film boiling was studied. The product of bubble diameter just leaving the vapor film and the frequecy of bubble formation takes constant value, if the radiation heat flux exceeds (1〜2) % of total heat flux, showing nearly the same numerical value as in case of nucleate boiling, but it decreases with the drop of radiation heat flux below the above-mentioned one. In other words, the behaviors of bubble generation in film boiling present different aspects according to the difference of emissivity of heating surface, even if the total heat fluxes remain the same. Though the results from the experimental values of heat transfer coefficient show fairly good agreement with Banchero's equation, the experimental points are somewhat lower than Banchero's equation below the heat flux in which the product of bubble diameter and frequency of bubble formation becomes constant. It will be, therefore, necessary to introduce a correlating equation, taking the vapor film stirring effect of generating bubbles into consideration.
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