The interaction of surface orientation and roughness on nanofluid sub-cooled flow boiling

Abstract

This experimental study examined the subcooled-flow boiling of water-alumina nanofluids with 0.1 vol % concentration. The study aimed to explore how surface roughness, fluid velocity, and surface orientation influenced the subcooled flow boiling heat transfer (SFBHT). A cross-sectional area of 2 × 3 cm2 and a length of 1.20 m are the dimensions of the plexiglass channel in the experimental setup. A copper heater was embedded at the bottom surface of the channel. The results of the experiment revealed that the surface roughness had a positive effect on SFBHT for horizontal channels, and it depended on the surface configuration. The heat flux increases by 233 % and 98.27 % at low and high fluid velocity (0.5 and 0.9 m/s) by changing the surface roughness from 0.65 to 4.4 μm, respectively. The fluid velocity did not have uniform impacts on SFBHT for higher and lower surface temperatures. When altering the fluid velocity from 0.5 m/s to 0.9 m/s, the heat flux experiences significant variations: The overall heat fluxes are 56.52 % and −35.86 % for rough surface at lower and higher surface temperature, respectively. Depending on whether the surfaces were smooth or rough, the SFBHT performance varied due to the surface configuration. The boiling heat transfer (BHT) performance increased for smooth surfaces but decreased for rough surfaces by changing the surface orientation in both negative and positive directions. The overall heat fluxes increase by about 72.84 % and 66.67 % at smooth surface for both positive and negative inclination, respectively. They are about −32.94 % and −29.82 % at rough surface for both positive and negative inclination, too. The rate of surface roughness’ effects on SFBHT reduces by enhancing the surface angles.