Heat transfer enhancement of an internal subcooled flow boiling over a hot spot

Using nanofluids is one of the most recent techniques for improving the boiling performance. The present paper investigates the impact of fluid velocity, nanoparticles addition, and surface characteristics, such as roughness, material and topography on the subcooled flow boiling, experimentally. An experimental setup consisting of a Plexiglas channel with the cross section of 20 × 30 mm2 and the length of 120 cm was used for this propose. A cylindrical heater with a diameter of 12 mm was located at the bottom surface of the channel. The experiments were conducted with four different heaters which were made of brass (with and without mini-grooves), aluminum and copper. The experimental results showed that the surface heat flux increases with an increase in the surface roughness and velocity. However, the impact of velocity on the heat flux is only observed at lower boiling surface temperatures and opposite trend has been seen for the higher boiling surface temperature. The experiments were also conducted for pure water and water-alumina nanofluids with a concentration of 0.1 and 0.25 vol.%. The nanofluid with the concentration of 0.25 vol.% has better heat transfer performance than the other ones. When the surface material was considered, brass showed a better boiling heat transfer performance than that of the copper and aluminum. The effect of mini-channels (grooves) on the performance of the nanofluid subcooled flow boiling showed that these grooves have enhanced the heat transfer significantly.