The enhanced dew-point evaporative cooling with a macro-roughened structure

Abstract

Dew-point evaporative cooling (DPEC) is renowned for its great cooling effectiveness and energy savings. However, to improve its cooling performance by optimizing the cooler's common design parameters (e.g., operating conditions and channel dimensions) has reached a bottleneck where further breakthroughs are difficult to make. Although macro-roughened structures have been found effective to enhance the heat transfer in many devices, the lack of fundamental studies and understanding on the enhanced heat and mass transfer limits their utilization in DPEC. Therefore, this study aims to investigate the enhanced DPEC with rib-roughened dry channels. A dew-point evaporative cooler with seven pairs of dry-wet air channels was constructed and tested under varying supply air and operating conditions, which demonstrated excellent cooling performance particularly at high air velocities. Concurrently, a novel low-Reynolds number computational fluid dynamics (CFD) model was developed to capture the turbulent heat and mass transfer mechanism, validated with a maximum discrepancy of 8% by the experimental data. An in-depth theoretical investigation of the rib-roughened channels show that detached vortices found near the ribs can enhance the convective heat transfer in the dry channel, as well as heat and mass transfer in the wet channel. The average Nusselt number in the dry and wet channels can reach 4 and 1.13 times of that in flat channels, respectively, and the average Sherwood number in the wet channel can reach 1.14 times. More enhanced cooling effect is observed under high air velocity conditions, leading to a reduction of product air temperature by 2.3–3.0 °C and an increase in dew-point effectiveness by 0.14–0.18. The fundamentally enhanced heat and mass transfer in the macro-structured channels provides a new research direction for the development of DPEC.