Evaporative cooling towers serve the heat rejection needs of a wide variety of industries. In a typical cooling loop, water is pumped through a steam condenser, chiller, or heat exchanger to a cooling tower, which rejects the heat to the atmosphere. In the majority of cooling towers, a fan on the top of the tower is used to induce an air stream against the falling water droplets. As the air comes in contact with the water, a small fraction of the water droplets are entrained in the exiting airstream. Baffles called drift eliminators are placed between the nozzles and the fan to minimize (through inertial impaction) the amount of entrained water droplets that are discharged into the atmosphere. The escaping droplets are called drift. An important distinction between drift and the normally visible condensing plume is that the drift contains the same chemicals and solids present in the circulating water, whereas the condensation is pure water vapor. Cooling tower emission rates are usually presented as a Drift Fraction which is defined as the ration of the water exiting the tower as drift divided by the circulating water flow rate. This paper discusses drift testing methods, the current state-of-the-art drift emission guarantees, and tower specifics that contribute to increased drift emissions.
