Numerical simulation of thermal performance for super large-scale wet cooling tower equipped with an axial fan

Abstract

For the super large-scale natural draft wet cooling towers (S-NDWCTs), the higher rain zone produces water dropping potential energy which can be used to drive an axial fan, meanwhile, the larger diameter deteriorate the whole ventilation performance. Based on these issues, a three dimensional (3D) numerical model for a S-NDWCT equipped with an axial fan was established to analyze the thermal performance at different fan diameters and fan power. In order to evaluate the influence of fan, one dimensionless number m, represents the ratio between the fan diameter and the cooling tower diameter, was introduced in this paper, as well as air velocity uniformity coefficient ψvel and air temperature uniformity coefficient ψtem. Simulation results manifested that, compared with natural draft pattern, the thermal performance and ventilation performance of S-NDWCT with an axial fan improve partly according to these two uniformity coefficient and several thermal performance parameters, and they improve continuously with the increasing of fan diameter and fan power. At the given fan rotate speed (20 rpm), the water temperature drop ΔT, ventilation rate G, Merkel number N and cooling efficiency η enhance persistently as the diameter of the fan increases, while these parameters enhance firstly, and then reduce at the given power (300 kW). Under 15.0 m fan diameter (m = 0.125) and 300 kW fan power conditions, compared with natural draft pattern, ΔT, G, N, and η all reach to the maximum of 9.31 °C, 31,549 kg/s, 1.65 and 53.5%, and enhance by 0.14 °C, 611 kg/s, 0.04 and 0.8%, respectively. It demonstrates that the cooling tower shows out the outstanding thermal and ventilation performance when the diameter ratio m is 0.125.