Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / Cooling tower rain zone performance characteristics such as the loss coefficient and the Merkel number are evaluated and simulated. To this end the influence of drop diameter and drop deformation on the velocity, path length and cooling of single water drops are investigated. Experimental drop size and pressure drop data over a counterflow rain zone are presented and the effect of drop deformation on the pressure drop is investigated using the experimental data and CFD. Using the experimental drop size data and CFD, the performance uncertainty produced by using the Rosin-Rammler drop distribution function as opposed to the discrete drop distribution data is investigated. CFD models are developed to investigate the feasibility of modelling rain zones by assuming a constant drop diameter and to establish which diameter definition is the most representative of a particular polydisperse drop distribution. These models were used to validate the correlations for the rain zone performance characteristics proposed in literature.