Sensitivity to heat and mass transfer correlations of the model for an evaporative condenser

Abstract

Evaporative condensers have established themselves in refrigeration plants for food process and storage owing to the combination of air and water cooling, with an overall reduction in energy (pumping) and fluid (water) consumption. Given the steep rise of electricity prices, the need to develop conduction strategies at the plant level which are less energy-intensive has driven the need for models to carry out simulations of the new strategies without actually impacting normal plant operations. This paper describes the development of a distributed-parameter model of an evaporative condenser with fill-pack, based on Merkel’s pioneering works on evaporative cooling. Several correlations are available for the heat and mass transfer coefficients, but none that satisfies the operating conditions of the case at hand, yet they are the most critical set of parameters for the model, therefore a sensitivity study has been carried out, to ascertain which combinations of transport coefficients out of a total of 288 would yield a total cooling power closest to the value declared by the manufacturer for a real-life evaporative condenser under rating conditions. This work demonstrates the applicability of the correlations examined, and also twenty of the examined combinations allow the model to reach a good agreement with the reference data (within ±5%). Further, the distributed-parameter structure of the model allows highlighting the reasons for good or bad performance of the correlations by determining the spatial distribution in the cooling coil and fill-pack of quantities such as moist air enthalpy and water temperature. The model and methodologies are a little cost-intensive in terms of computational time and can be applied to the study and design of any similar piece of equipment.