Natural Convection Film Boiling on a Sphere
Immersing a solid into a liquid produces film boiling if the surface temperature is above the Leidenfrost point, Aside from cryogenic applications, metallurgists have tested the cooling abilities of liquids by dropping a hot sphere or other bodies into a liquid bath . The boundary layer type of film boiling can be easily analyzed for steady state conditions if the film is laminar. This analysis also may be applied to a transient test if the change in enthalpy of the vapor film is much smaller than that of the solid, as it is in the tests described later. Therefore when “slow” cooling takes place with respect to the vapor film, quasi-stationary film boiling may be assumed to occur and be so described analytically. An analysis is presented in which a diffusion approximation is made by linearizing the governing equations. The approximate result serves as a guide to a generalized correlation of film boiling heat transfer data.
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