Experimental study on the performance of a mechanical cooling tower fitted with different types of water distribution systems.

Résumé

Cooling towers are evaporative heat transfer devices in which atmospheric air cools warm water, with direct contact between the water and the air, by evaporating part of the water. As a result, water droplets are incorporated in the air stream and, depending on the velocity of the air, will be taken away from the unit. This is known as drift. Although cooling tower drift is objectionable for several reasons, the most hazardous problem concerning human health is the emission of chemicals or microorganisms to the atmosphere. Regarding to microorganisms, the most well-known pathogens are the multiple species of bacteria collectively known as legionella.The binomial water distribution system-drift eliminator is identified to be the main responsible of cooling tower drift. While drift eliminators work by changing the direction of the airflow and separatingdroplets from the airstream through inertial impact, water distribution systems affect the mechanics of setting up the drops.Drift eliminator’s performance can be quantified mainly by two factors. On one hand the droplet collection efficiency and, on the other hand, the pressure drop across the eliminator. In contrast, waterdistribution systems are characterized by the pressure drop across itself and the achieved size of the particles spread. Although the factors mentioned above are conditioned by the binomial waterdistribution system-drift eliminator, it affects mainly the quantity of water taken away from the tower and the thermal performance. From the reviewed bibliography, some studies assessing the effect of the drift eliminator on cooling tower’s performance have been found. Nevertheless no studies regarding the influence of the waterdistribution system on cooling tower’s performance have been found. In this sense, this paper studies the thermal performance of a forced draft counter-flow wet cooling tower fitted with different waterdistribution systems for many drift eliminators for a wide range of air and water mass flow rates. The data registered in the experimental set-up were employed to obtain correlations of the TowerCharacteristic, which defines the cooling tower’s thermal performance. The outlet water temperature predicted by these correlations was compared with the experimentally registered values, obtaining amaximum difference of ±0.95%.