Variable Property Effects on Vapor Condensation with a Noncondensable Gas
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In modeling condensation from vapor-gas mixtures with the heat and mass transfer analogy, there are two parallel methods in the literature to account for variable property effects: (a) the property ratio scheme using an empirical factor as a multiplier for the mass flux and (b) the reference property scheme using reference properties to calculate the mass flux. The current work focuses on the reference property scheme and establishes its relation to the property ratio scheme. From condensation boundary layer analysis, the current work proposes a reference mixture composition and a reference mixture temperature, which can be used for calculation of a variety of reference thermodynamic and transport proper-ties. It is demonstrated that the empirical factor in the property ratio scheme used widely in the literature can be obtained from the reference property scheme derived in the current work, and thus, the two parallel methods to account for variable property effects are equivalent. A common mistake in using the reference mixture composition is highlighted as part of this investigation. The reference property scheme presented herein has a theoretical basis and is more accurate over a wide range of conditions than the empirical property ratio scheme. Finally, the reference property scheme is extended to multi-component gases.
