Experimental investigation of velocity and roughness effects on subcooled flow boiling

The subcooled flow boiling occurs when the bulk temperature is less than saturation temperature of the liquid at that pressure while the surface temperature is higher. The most importance of boiling phenomenon is related to the high latent heat of fluid which could removes high heat flux at relatively low temperature difference between liquid and the hot surface. In this study, the impact of velocity and roughness on the subcooled flow boiling were investigated experimentally for pure water. An experimental setup was designed and manufactured. The experimental setup consists of a plexiglass channel with cross section 20×30 mm and the length of 120 cm. A cylindrical heater with diameter 12 mm made of copper is located on the bottom surface of the plexiglass channel. All the experiments were conducted for the surface roughness of 0.65, 2.5 and 4.4 µm at velocities of 0.5, 0.7 and 0.9 m/s. The experimental results show that the surface heat flux increases as the surface roughness and velocity increases. However, this affect of velocity enhancement was only observed for lower boiling surface temperature and opposite trend has taken place for higher boiling surface temperature. This is due to the simultaneous consideration of the convection and boiling terms along with the interaction between them which has not been presented experimentally yet. It appears that this kind of experimental study has not been carried out for copper type surfaces.