Radar Measurement of Cooling Tower Drift

Abstract

A method of radar measurement of drift, generated by the wet cooling towers of power plants, is proposed. The water given off by the evaporative towers consists of two kinds of droplets: the recondensation droplets?generally less than 20 ?m in diameter and with a negligible rate of fall?and the drift droplets, arising from spraying of cooling water, entrained out of the tower in the exhaust air flow. Both components partake in the radar reflectivity of the plumes. A very close relation is found between the water content and the reflectivity factor of the recondensation cloud. For a same liquid water content, the reflectivity of the recondensation cloud is 20 dB lower than that of warm cumulus clouds. The knowledge of the cooling tower working point and of the surrounding air conditions enables the evaluation of the recondensation cloud contribution to the reflectivity. In the next step, assuming that the drift droplet population is represented by a gamma distribution, functional relations are developed enabling the computation of the number density, the water content and the precipitation rate of cooling tower drift from the radar reflectivity factor of the drift component. Some observations are presented to illustrate the proposed method and to show that, owing to the presence of the cooling droplets, the radar outlines of the plume noticeably differ from its visual outlines. The radar thus enables a quantitative monitoring of the microstructure of the plumes emitted by the atmospheric cooling tower parks, i.e., a measurement of the efficiency of the drift droplet eliminators.