deluge, spray, evaporative cooling, hybrid wet-dry cooling, visualization
At high ambient temperature, the air cooled HX capacity can be boosted by using evaporation of a water film applied directly on the heat exchanger surface in deluge, spray, or mist cooling mode. In order to accurately determine evaporatively cooled HX capacity, it is critical to know the portion of fin area wetted. However, wetting inherently is a highly non-uniform phenomenon dependent on the method of application, evaporation rate and air velocity. Furthermore, for typical optimized air cooled HXs the fin geometry is often complex and spacing narrow. This study presents a novel method to quantify HX wetted fin area through enhanced visualization in HX depth and sectional flow rate measurement. Flow maps for deluge and front spray cooling are presented at varying inlet air velocities and wetting water flow rates. This study confirms that a significant portion of HX remains dry which contributes to low experimentally obtained HX heat transfer rates, irrespective of wetting method even under moderate to high wetting water flow rates. Furthermore, it highlights the need for developing HX wetting technologies that ensure uniform wetting at lowest wetting flow rates.