ANALYTICAL INVESTIGATION ON THE CONDENSATION PERFORMANCE OF VERTICAL, TILTED AND HORIZONTAL SURFACES FOR PASSIVE WATER HARVESTING

Abstract

Condensate harvesting is the phenomenon of obtaining water from water vapor in the humid air condensing on a surface. The idea is a passive technique with no additional energy consumption, yet condensation performance of a surface varies with many parameters. This study analytically investigates the condensation performance of the vertical, tilted, and horizontal water harvesting systems. First, viscous effects, inertia, and gravitational forces are examined in detail to express the evolution of boundary layer in condensation film. Then the condensation performance of each surface orientation and tilt angles are documented and compared for all flow conditions. Although vertical surfaces have higher condensate harvesting performance compared to the tilted and horizontal systems, the condensation rate is only about 2% lower up to 15⁰ tilt angle. When the harvesting surface is tilted at 30⁰, the condensation rate of the laminar film decreases by 3.5%, while the reduction is 4.7% in wavy-turbulent film condensation. The results indicate that the change in condensation rate is more evident just after 45⁰ tilt. Furthermore, 89⁰ tilted surfaces experience 63.7% and 74.1% lower condensate harvesting in laminar and wavy-turbulent regimes, respectively. In addition, identical horizontal surfaces produce only one fifth condensation rate of a vertical system.