IMPROVEMENT OF THE EFFICIENCY OF THE OPERATION OF COUNTERFLOW COOLING TOWERS BY MEANS OF NEW PERFORATED PLASTIC PACKING: AN EXPERIMENTAL INVESTIGATION AND MATHEMATICAL MODELING APPROACH

Abstract

A cooling tower is an important element of industry equipment which ensures dissipation of excess heat via simultaneous heat and mass transfer of water and air streams. The thermal efficiency of cooling towers depends on the packing which offers an effective surface area for evaporative cooling. Polymer packings are used in the majority of industrial cooling towers due to their low price, durability, and anti-corrosion properties; but the lack of wettability and non-uniform distribution of water in these packings can restrict efficiency, especially in critical operational conditions. Hence, optimization of geometric parameters of packing to increase heat and mass transfer efficiency becomes a key issue in modern research. In this study, the thermal performance of a laboratory-scale counterflow cooling tower with novel perforated plastic packings made of transparent acrylic plates using CNC cutting technology is investigated experimentally. Various geometrical packing structures were analyzed using variations in the perforation ratio, shape of holes, hole diameter, and thickness of plates in different values of liquid-to-gas mass flow ratio (L/G). The thermal performance was characterized by such indices as reduction of water temperature, efficiency of the cooling tower, volumetric mass transfer coefficient Ka V/L and heat removal rate. Moreover, a theoretical mathematical model based on the principles of Merkel theory was developed for estimation of the thermal characteristics of the cooling tower and validation of experimental data. The obtained results demonstrate that the geometry of holes has a great effect on the thermal performance: circular holes provide the best thermal efficiency of the packing due to more uniform water distribution and lesser aerodynamic resistance compared to other types of holes. The optimal packing which guarantees maximum efficiency and volumetric mass transfer coefficient consists of packing with 10% perforation ratio, 2 mm holes and 1 mm thickness of plates. The proposed Merkel model proved good correspondence with experimental data: the accuracy of predictions exceeded 95%. Novel perforated plastic packing can be considered a perspective way of improvement of efficiency of cooling towers in the conditions of low cost and simple manufacturing.