Numerical simulation of evaporative cooling process in a medium-gap-medium arrangement

Abstract

Wet medium is the key components of direct evaporative cooling system, and its performance affects the cooling performance extensively. The medium arrangement contributes much to good cooling performance of direct evaporative cooling system. The current paper continues previous experimental study of medium-gap-medium arrangement of wet medium, aiming to investigate the heat and mass transfer mechanism in such novel arrangement. A 3-D model was established using Fluent 18.0 to simulate the heat and mass transfer process in medium-gap-medium arrangement of wet medium. The airflow field, air temperature, humidity distribution and pressure drop were explored. The effects of the widths of the air gap, ambient dry-bulb temperature, wet-bulb temperature, and air speed on the cooling performance of medium-gap-medium arrangement were studied. Simulation based on the condition of air dry-bulb temperature of 27 °C, wet-bulb temperature of 19 °C, air speed of 1.5 m s−1, finds that: (1) the air temperature drops flowing through the 100 mm medium, 100 mm gap and 100 mm medium successively are 4.3 °C, 1.3 °C and 1.6 °C, respectively. The two 100 mm medium zones accounts for 82.5% cooling of the total cooling effect while the 100 mm gap zone accounts for 17.5% cooling as there exists water rain in the gap zone; (2) the pressure drops of the first 100 mm medium zone, the 100 mm gap zone and the second 100 mm medium zone are 7.97 Pa, 0.31 Pa and 7.93 Pa, respectively. (3) a decrease in the cooling efficiency over 11% can be attained when the air speed changes from 0.5 m s−1 to 3.0 m s−1.