Investigation of humid air physical properties influence on the heat and mass transfer processes calculation accuracy

Abstract

Humid air is a mixture of dry air and water vapor and is widely used in various power and technical devices. Most theoretical studies of the properties of humid air are based on Mendeleev-Clapeyron ideal gas equa-tion, which doesn’t take into account the association, intermolecular interaction, and particularities of the thermodynamic behavior of humid air as a mixture of gases. The use of this equation leads to inaccuracy in determining the parameters of the state of humid air, which can reach up to 55 %. Therefore, the issues con-cerning the actual properties of humid air determining remain poorly understood. The ideal gas model is based on Mendeleev-Clapeyron equation. To study the actual parameters of the humid air state and its properties, Vukalovich-Novikov’s and Molie’s real gas state equations have been used.Several equations of the state of real gas, taking into account the interaction of water vapor molecules have been considered. The actual physical properties of humid air are determined, and their influence on the coupled heat and mass transfer processes for various conditions is evaluated. The actual values of the thermophysical properties of humid air have been derived. The thermodynamic limits for humid air have been determined using Mendeleev-Clapeyron’s, Vukalovich-Novikov’s and Molie’s state equations. It has been proved Vukalovich-Novikov’s state equation to be the best to represent the quantitative relations between the pressure, specific volume, and the temperature of saturated water vapor. Its application reduces the error of calculations by 39–50 %. The results obtained allow to improve the accuracy of calculating heat and mass transfer when designing contact heat exchangers, convective drying units and hygroscopic desalination plants, compression processes with water or water vapor injection, as well as the processes of mixing flue gases with water vapor in the combustion chambers of gas-steam installations.