Parametric CFD Analysis of Two Natural Draft Wetcooling Towers With Isotropic Fills

摘要

In the design of a modem natural draught wet-cooling tower, structural and performance characteristics must be considered. Air flow distortions and resistances must be minimised to achieve optimal cooling which requires that the cooling towers must be modelled two-dimensionally and ultimately threedimensionally to be optimised. CFD models in literature are limited to counterflow cooling towers packed with film fills, which are porous in one direction only and generally have a high pressure drop, as well as purely crossflow cooling towers packed with splash fill, which simplifies the analysis considerably. Many counterflow cooling towers are however packed with trickle and splash fills which have anisotropic flow resistances, which means the fills are porous in all flow directions and thus air flow can be oblique through the fill, especially near the cooling tower air inlet. This provides a challenge since available fill test facilities and subsequently fill performance characteristics are limited to purely counter-and crossflow configuration.In this paper, parametric studies are done on two different natural draught wet-cooling towers (NDWCTs) using a parametric CFD model developed to predict the performance of NDWCTs with any type of fill and design configuration. The fill performance characteristics for oblique air flow are determined by linear interpolation between counter-and crossflow fill characteristics in terms of the air flow angle. The CFD results are validated by means of corresponding one-dimensional computational model data. The objective is to investigate the effects of different air inlet and outlet geometries, air inlet heights, cooling tower inlet and outlet diameters, rain zone drop size distributions, variations in radial water loading and fill depth and fill configurations on cooling tower performance for optimisation purposes. The results show that NDWCT performance can be enhanced significantly.