More than 400 pieces of test sections-flat plates made of various metals and alloys-were placed in saturated water under atmospheric pressure and heated to physical destruction by passing electric current directly through them.Several non-hydrodynamic parameters have marked effect upon the critical heat flux, which indicates that purely hydrodynamic theories are not directly applicable to general prediction of the critical heat flux.The critical heat flux data was found to be well correlated with tbe heat capacity per unit surface area of the test section: the critical heat flux is reduced with decrease of this parameter, while with increasing parameter it approaches a certain asymptotic value.The fluctuation of surface temperature due to alternate contact with vapor and liquid was calculated hy the proposed model, and the trend of dryout duration was estimated from the critical heat flux data.
Heat transfer and critical heat flux in saturated pool boiling were experimentally studied under transient power condition. The heating elements were flat plates of nickel submerged facing vertically in sta,unant water. The heat generation rate in the test section was increased linearly in time, upon which, under certain conditions the heat flux was found to reach a maximum point located in the nucleate boiling regime. The hea~ flux of this critical point increased with mounting sharpness of the transient, and the mechanism that occurs such a high critical heat flux may be the rapid formation and evaporation of thin liquid film at the bases of vapor bubbles. Examination of high speed motion pictures reveals that all bubbles on the heating surface are still in the phase of the first generation until the critical condition is reached. Compared to the case of steady boiling, the effect of differences in the heat capacity of the test section upon the critical heat flux was found to be less marked under the present experimental conditions.
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