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

Abstract

Nomenclature AbstractCooling 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. The principle of operation of cooling towers requires spraying or distributing water over a heat transfer surface (packing) across or through which a stream of air is passing. 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 into the atmosphere. Undoubtedly, regarding 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 that mainly responsible for cooling tower drift. While water distribution systems affect the mechanics of setting up the drops, drift eliminators work by changing the direction of the airflow and separating droplets from the airstream through inertial impact.The drift eliminator's performance can be quantified mainly by two factors: droplet collection efficiency and the pressure drop across the eliminator. In contrast, water distribution systems are characterized by the pressure drop across itself and the achieved size of the particle spread. Alongside drift, the binomial water distribution system-drift eliminator affects the cooling tower performance.From the reviewed bibliography, some studies assessing the effect of the drift eliminator on cooling tower performance have been found. Nevertheless, no studies regarding the influence of the water distribution system on the cooling tower's performance have been detected. In this sense, this paper studies the thermal performance of a forced draft counter-flow wet cooling tower fitted with two water distribution systems (the pressure water distribution system (PWDS) and gravity water distribution system (GWDS)) for six 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 tower characteristic, which defines the cooling tower's thermal performance. The outlet water temperature predicted by these correlations was compared with the experimentally registered values, obtaining a maximum averaged difference of ±0.95%.

Optimum Design and Operation of an HVAC Cooling Tower for Energy and Water Conservation

“…Furthermore, as reported in the previous section, 12 simulations were carried out to determine the influence of the cooling tower elements (drift eliminator and water distribution system) on energy and water consumption of the system in a Mediterranean climate (Alicante, Spain). The cooling tower configurations defined in the work of Lucas et al [13] were taken as a reference. The authors considered for their experimental tests 6 different drift eliminators (defined from A-F), 2 water distribution systems (pressure water distribution system (PWDS) and gravity water distribution system (GWDS)) and 3 levels for water and air mass flow rates, respectively, for a total of 108 tests.…”

“…As the results forẆ fan for different frequencies and configurations were not initially available in the literature, some ad hoc experiments were conducted in order to assess the validity of the model prediction. In this sense, 120 experimental tests were carried out in the same experimental pilot plant and for all 12 cooling tower configurations (combination of drift eliminator and water distribution system) described in Lucas et al [13]. The frequency of the fan ( f ) was fixed at 10 levels (ranging from 5-50 Hz, in 5-Hz intervals).…”

“…As general correlations for heat and mass transfer in cooling towers in terms of the physical tower characteristics are not readily available, constants c and n in Equation (16) have been taken from the work of Lucas et al [13].…”

“…The tower characteristic was also correlated with water-to-air mass flow ratios for six different drift eliminators, obtaining an average difference between them of 46.54%. Regarding the distribution system, Lucas et al [13] analyzed the influence of a film flow (gravity) and a splash (pressure) water distribution system and six different drift eliminators on the cooling tower performance. The obtained results were compared with other works that used a splash-type pressure water distribution system, assessing the best cooling tower performance.…”

Numerical Study and Experimental Validation of the Water Films and the Detachment of Drops on Drift Eliminators

“…The water enters the cooling tower by spray, or by free fall, with a crossflow airstream. Surface evaporation of a small part of the water induced by contact with air results in the cooling of the rest of the water falling on the raft [1].…”