Condensation heat transfer in the presence of noncondensables, interfacial resistance, superheating, variable properties, and diffusion

W. J. Minkowycz, E. M. Sparrow

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Abstract

A wide-ranging analytical investigation of laminar film condensation is presented. The situation under study is an isothermal vertical plate with steam as the condensing vapor and air as the noncondensable gas. In addition to the noncondensable gas, the analytical model includes interfacial resistance, superheating, free convection due to both temperature and concentration gradients, mass diffusion and thermal diffusion, and variable properties in both the liquid and the gas-vapor regions. Heat-transfer results are obtained for a wide range of parameters including bulk concentration of the noncondensable gas, system pressure level, wall-to-bulk temperature difference, and degree of superheating. It is demonstrated that small bulk concentrations of the noncondensable gas can have a decisive effect on the heat-transfer rate. For instance, for a bulk mass fraction of air equal to 0.5 per cent, reductions in heat transfer of 50 per cent or more are sustained. The influence of the noncondensable gas is accentuated at lower pressure levels. It is shown that the aforementioned reductions in heat transfer are due entirely to the diffusional resistance of the gas-vapor boundary layer. The interfacial resistance is shown to be a second order effect. A similar finding applies to thermal diffusion and diffusion thermo. The effect of superheating, which is very small in the case of a pure vapor, becomes much more significant in the presence of a noncondensable gas. A reference temperature rule is deduced for extending the Nusselt model to variable-property conditions.

Original languageEnglish (US)
Pages (from-to)1125-1144
Number of pages20
JournalInternational Journal of Heat and Mass Transfer
Volume9
Issue number10
DOIs
StatePublished - Oct 1966

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