An experimental investigation of the drift ratio and its influencing factors in mechanical draft wet cooling towers

The drift ratio is a key indicator of the water-saving performance of cooling towers. However, quantitative experimental studies on the drift ratio remain limited. To address this issue, this study establishes a drift rate test platform and conducts 96 experiments on the droplet loss of water caused by drift loss and droplet dripping, using a mechanical draft wet model tower and the filter paper moisture absorption method. The characteristics of the drift droplets and floating water volume are analyzed, along with the variation patterns of the drift ratio, and a three-variable prediction model is proposed. Experimental results indicate that the drift ratio of cooling towers is not governed by a single factor, but is jointly influenced by the nozzle diameter, water drenching density, and sectional wind velocity, exhibiting nonlinear behavior. Among these factors, the nozzle diameter plays a critical role, while the sectional wind velocity and water drenching density exert a synergistic regulatory effect. Detailed analysis reveals that increasing the sectional wind velocity consistently results in a nonlinear increase in the drift ratio. With increasing sectional wind velocity, small-diameter nozzles (D ≤ 34 mm) produce higher drift ratios than large-diameter nozzles (D ≥ 36 mm). Moreover, as the water drenching density increases, the drift ratios of small-diameter nozzles rise and peak at 13 t/(h·m²), whereas those of large-diameter nozzles decrease, peaking at 7 t/(h·m²). To further quantify the influence of these factors, an exponential regression model for the drift ratio is developed as a function of the water drenching density and sectional wind velocity, grouped by nozzle diameter, achieving a goodness of fit exceeding 98%. This study provides a valuable reference for nozzle selection and water-saving design in wet cooling towers for engineering applications.