Sweating-boosted air cooling using nanoscale CuO wick structures

Abstract

Low heat transfer coefficient (HTC) in air/fin-side is the bottleneck of dry cooling strategies for thermal power plants. Inspired by the phase change heat transfer during the perspiration of mammals, a sweating-boosted air cooling strategy with on-demand water dripping is proposed. The testing samples are featured with macroscale grooves for global liquid delivery, and with nanoscale hydrophilic copper oxide (CuO) wick structures for local liquid spreading. The experiments of sweating-boosted air cooling are conducted in a wind tunnel system. There are three wetting conditions with increasing dripping rates: dry, partially wetted, and flooded conditions. In the partially wetted conditions, the surface temperatures reduce and HTCs increase with increasing dripping rates. For a given dripping rate of water, HTCs are enhanced and surface temperatures are reduced with increasing air velocities. High air velocity and low surface temperature have a trade-off effect on the evaporation process. This effect results in almost constant saturated dripping rates for a given thermal load. A linear relationship between the saturated dripping rates and the thermal loads confirms that the evaporation dominates the heat transfer process of sweating-boosted air cooling. Complete surface wetting is obtained on the designed surfaces, but no obvious effect of groove width on HTCs is observed. Sweating-boosted air cooling can significantly increase air-fin side HTC in air cooled condenser (ACC), and dramatically reduce the water consumption compared to current water evaporative condenser (WEC). This research provides a fundamental understanding on the sweating-boosted effects on the air cooling.