Selection of wetted media for pre-cooling of air entering natural draft dry cooling towers

Abstract

The performance of natural draft dry cooling towers (NDDCTs) can be improved by wetted-medium evaporative pre-cooling. However, the pre-cooling benefit is season dependent and is significantly affected by wetted media. To further investigate the effect of wetted medium type on pre-cooling performance, the current study simulates a pre-cooled NDDCT using two typical types of wetted media, i.e., film (Cellulose7060 and PVC1200) and trickle (Trickle125 and Trickle100). A MATLAB program was developed and was validated against published data. The model was then used to carry out case study of a 120m-high NDDCT pre-cooled using the selected wetted media with fixed thickness of 300mm. Both the medium performance and pre-cooled NDDCT performance were compared to recommend the characteristics of wetted media promising for evaporative pre-cooling. Simulation finds that the media with high or low cooling efficiencies and pressure drops are not promising for the studied pre-cooling case while those media with middle cooling efficiencies and pressure drops intend to produce much performance enhancement and Cellulose7060 is a representative of such kind of medium. For the 120m-high NDDCT, the wetted-medium pre-cooling can raise the heat rejection rate of the tower without pre-cooling from 45MW to 92MW, 76MW, 68MW and 65MW by Cellulose7060, PVC1200, Trickle125 and Trickle100, respectively at ambient temperature of 50°C and humidity of 20%.