ANALYTICAL STUDIES OF THE HEAT AND MASS EXCHANGE PROCESS OF AN AIR HEAT EXCHANGER

Abstract

The paper presents the results of analytical and numerical study of heat and mass transfer processes in an indirect-evaporative air heat exchanger with cross-flow organization. A physical and mathematical model is proposed, based on the equations of conservation of mass, momentum and energy and takes into account the combined effect of sensible heat transfer and latent heat of phase transition in wetted channels.

An algorithmic scheme for numerical implementation of the model is developed, taking into account the redistribution and local mixing of air flows between dry and wetted channels. Based on the developed methodology, CFD modeling was performed in the STAR-CCM+ software environment in order to obtain spatial distributions of temperature, absolute humidity and velocity fields in characteristic zones of the heat exchange matrix.

According to the results of numerical analysis, the presence of spatial heterogeneity of the thermal regime and velocity gradients in wetted channels was established, which significantly affects the intensity of heat and mass transfer and aerodynamic losses. It is shown that within the indirect evaporation scheme, the main air flow in dry channels is cooled without increasing the moisture content, while the increase in absolute humidity occurs mainly in the working flow passing through the wetted channels.

Based on the results of numerical analysis, a new heat exchanger design was developed, aimed at increasing the uniformity of the velocity distribution and intensifying heat transfer. To verify the adequacy of the numerical model, an experimental sample was manufactured and a laboratory stand with an automated data acquisition system was created. The experimental results demonstrated satisfactory consistency with CFD calculations, which confirms the correctness of the developed physical and mathematical model and the feasibility of its use for engineering design and optimization of indirect evaporation-type air heat exchangers.