Experimental determination of water carryover in the airstream from PVC evaporative cooling pads

The increasing need for energy-efficient cooling strategies in buildings has renewed interest in Direct Evaporative Cooling (DEC) as an alternative to compression-based systems. However, it introduces engineering challenges such as the risk of microbial growth and its subsequent dissemination into the supply air as aerosols. Compared to DEC misting, wetted media pads do not inherently generate aerosols, although water entrainment may occur if operating at high air velocities. This phenomenon of water carryover, defined as the unintended entrainment of liquid droplets into the outlet airflow, remains insufficiently documented, particularly in synthetic media such as corrugated PVC. This gap is not merely academic: uncontrolled entrainment may have significant operational and hygienic implications in relation to aerosolized water and pathogen dispersion. This study offers a detailed experimental characterization of water carryover in a commercial PVC evaporative pad. The sensitive paper method was used to assess droplet deposition patterns and quantify entrainment under a range of operating conditions. Air flow rates varied between 500 and 1500 l s −1 , with water loading set between 40 and 80 l min −1 m −2 . The results indicate that the entrainment remains negligible, on the order of 1 0 − 6 kg s −1 , at air flow rates below 1000 l s −1 , but increases significantly beyond that threshold, reaching values as high as 1 0 − 4 kg s −1 under more demanding conditions. Most droplet diameters were within 20– 30 μ m , except in specific cases, 1250 and 1500 l s −1 , where significantly larger droplets were observed.