INFLUENCE OF AIR VELOCITY ON EVAPORATIVE COOLING PERFORMANCE OF A NOZZLE-EQUIPPED MIST FAN: A CFD STUDY

Abstract

Air velocity is a critical operating variable in fan-assisted evaporative cooling because it controls droplet residence time, droplet dispersion and the spatial development of the cooled air field. This study investigates the influence of air velocity on the cooling performance of a nozzle-equipped mist fan using three-dimensional computational fluid dynamics (CFD). A fan-driven mist system was represented using a Lagrangian–Eulerian multiphase formulation, with air as the continuous phase and water droplets as the dispersed phase. The analysis was performed with the optimum nozzle arrangement identified in the wider study, while air velocity was varied at 2.0, 5.96 and 10.0 m/s. Cooling efficiency, average air temperature and relative humidity were evaluated on the Plane_0.9 monitoring plane. The detailed CFD results gave cooling efficiencies of 71%, 59% and 35% at 2.0, 5.96 and 10.0 m/s, respectively. Corresponding average temperatures were 302.3, 303.7 and 306.5 K, while relative humidity was 73%, 68% and 53%. The results show a clear deterioration in evaporative cooling effectiveness as air velocity increased. The reduction is associated with shorter effective droplet residence time and changes in droplet dispersion, which reduce the opportunity for evaporation and spatial interaction between the spray and airflow. The findings establish air velocity as a major control parameter for fan-assisted mist cooling and indicate that high air movement should not be selected solely on the basis of airflow delivery when evaporative cooling is the primary objective.