On the Diagnosis and Conservation of Energy During Condensation

Abstract

The diagnosis and conservation of energy during condensation is examined. It is shown that the latent enthalpy, when defined in conjunction with the individual enthalpies of water vapor and liquid water, cannot be a function of the latent heat of condensation L but a modified value (L?) which is ?30% larger than L. The additional energy represented in L? can be thought of as a necessary absorption by the liquid water to bring the post-condensation air-vapor-liquid system into thermal equilibrium. The difference between L? and L is a function of the difference in specific heats of water vaper and liquid water. If we assume that (Cpd?Cpr is constant, as is required in our energy conservation derivation, L? is shown to vary by only 0.59% when computed over the range ?50 to +60°C; a representative value for L' is 3.142?106 J Kg?1