Three-dimensional modeling of a dew-point evaporative cooler using a modified boundary condition and considering effects of channel's entrance regions

This paper presented a numerical modeling of dew-point counter-flow indirect evaporative coolers as a potential alternative to the conventional cooling systems. Unlike the conventional method of assuming constant surface heat (mass) flux or constant surface temperature boundary condition on the separating wall, the present article calculated real boundary conditions. Real boundary conditions were obtained by simultaneous solving of momentum, energy and mass transfer equations of the two flows coupled on the wall. Calculating real boundary conditions lead to a real distribution of humidity ratio and temperature on the separating wall where at each point, the summation of heat fluxes from air streams in adjacent channels is equal to the latent heat of evaporation at that point. Moreover, the model accuracy was increased through considering hydrodynamic and thermal developing flows of two air streams. The model predicted supply air temperature under different conditions, and the results were compared against experimental data as well as previous numerical models. It was shown that the maximum deviation of the supply air temperature was under ±3.3%. Then, a parametric analysis was conducted, which studies the effects of the inlet air velocity, channel gap, channel length and returned air ratio on the supply air temperature, dew-point effectiveness, cooling capacity and pressure drop. The results indicated that increasing channel length and returned air ratio, and reducing channel gap and inlet air velocity improved the dew-point effectiveness but increased the initial cost and pressure drop and decreased the cooling capacity.