A Method to Determine the Performance Characteristics of Cooling Tower Spray Zones

Cooling tower spray zones play an important role in cooling tower performance. Ideally they must distribute the cooling water uniformly onto the fill and must produce small drops at minimal pressure head to maximise heat and mass transfer in the spray zone with minimal pumping power. Limited thermal performance characteristic data is found in literature for cooling tower spray zones, since it is virtually impossible to measure spray zone performance accurately. In this paper, the method used to model the performance of cooling tower spray zones and results obtained for a medium pressure swirl nozzle are presented. Water flow distribution and drop size distribution tests are conducted on cooling tower spray nozzles to investigate the effects of varying different operating parameters, such as air and water flow rates, and installation parameters, such as nozzle height, nozzle spacing and direction of spray, on performance. The suitability of superimposing single nozzle flow distribution data to obtain the water distribution for a grid of equally spaced nozzles with variable nozzle spacing is investigated. Furthermore, a single nozzle simulation model is developed and used to model single spray nozzles. The single nozzle model and the superposition model are subsequently used to obtain initial drop conditions to model the spray zone using the commercial CFD package FLUENT®. The proposed modelling approach allows for the evaluation and performance prediction of existing and new nozzle design configurations. Correlations are presented for the Merkel number and loss coefficient for the downspray nozzle investigated.