Experimental investigation of capillary-assisted solution wetting and heat transfer using a micro-scale, porous-layer coating on horizontal-tube, falling-film heat exchanger

An experimental study was conducted to investigate the effect of a micro-scale, porous-layer coating on solution wetting and heat transfer of a horizontal-tube, falling-film heat exchanger. A uniform layer of a copper powder was sintered onto plain copper tubes to create a micro-scale, porous coating on the tubes. Distilled water was used as solution and heating fluids. When the solution was dripped onto horizontal tubes, the visual observation confirmed that plain tubes were partially wetted, while the porous-layer coated tubes were completely wetted due to capillary action even at low solution flow rates. The comparison of the heat transfer results for two different tube surfaces (plain and porous-layer coated) clearly showed that the porous-layer coated tubes had twice as high evaporation heat transfer rate due to the complete solution wetting and higher heat transfer coefficient due to the thin spreading of the solution liquid.