Simplified models for direct and indirect contact cooling towers and evaporative condensers

This paper presents a simplified method of analysing the combined heat and mass transfer phenomena in direct and indirect contact cooling towers and evaporative condensers. The theoretical basis of the model is Merkel's theory. The cooling towers, evaporative condensers and fluid coolers are considered as members of a classical heat exchanger family, working in wet regime. Here, the air side heat and mass transfer processes are governed by the same basic process. This paper shows that a 'unified' theoretical treatment may be applied to all three evaporative exchangers. The key difference in the theory for each type relates to these exchangers unique characteristic, the global heat transfer coefficient AU, or the corresponding thermal resistances of the fluids. Specific correlations for the calculation of AU or of the equivalent thermal resistances, considering the influence of the water and air flow rates entering the exchangers, are discussed. An example for each case is shown, illustrating the validation of the models with catalogue data.