Effect of surface roughness on pool boiling heat transfer in subcooled water-CuO nanofluid

We investigated the effect of surface roughness on pool boiling heat transfer in subcooled water-CuO nanofluid. Experiment was performed using 0.1% volumetric water-CuO nanofluid and pure water for comparison. The following results were obtained. The heat flux tended to increase as the liquid subcooling increased in the region of low wall superheat. However, the effect of liquid subcooling gradually decreased as the wall superheat increased. The heat flux of pure water and nanofluid was almost similar in the region of low wall superheat. As the wall superheat increased, however, the heat flux of nanofluid decreased compared to that of pure water. This was attributable to the fact that the nanoparticles mixed with pure water reduced the heat flux by deteriorating boiling on the heat transfer surface. The heat flux increased as the surface roughness increased in the pure water, but the effect of surface roughness on heat flux was unclear in the nanofluid. This was attributable to the decreased difference of surface roughness, which was caused by the coating or deposition of nanoparticles on the heat transfer surface during the experiment.