Subcooled forced convection film boiling over spheres and cylinders



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A theoretical treatment is presented for the heat transfer rates over spheres and cylinders in forced convection film boiling when the liquid bulk is subcooled to any degree. With the help of suitable assumptions, solutions for temperature profiles in liquid and vapour boundary layers are obtained which are then used to formulate a total energy balance on the sphere surface. The resulting equation is solved numerically to determine vapour film thickness at every point on the sphere body. Dimensionless Nusselt numbers are then computed for any given system parameters k[subscript 1] and k[subscript 2] (dimensionless), which can be looked upon as a general solution to the problem. It is confirmed that subcooling of the liquid bulk raises the heat transfer substantially. A number of comparisons with experiment are made which in general show a reasonably good match between the theory and the experimental trend. Theoretical fluxes obtained are about one half the experimental values.