Boiling heat transfer enhancement with stable nanofluids and laser textured copper surfaces

The rate of heat removal is an important factor which influences the efficiency of industrial processes. Due to this reason, methods to improve it is an active research topic. Of particular interest to the current study is the boiling heat transfer process which can potentially be enhanced by the use of nanofluids and textured surfaces. Even though many studies have been conducted to determine the heat transfer ability of nanofluids, controversy exists in the results published so far. We gathered from the literature that the stability of nanofluids used in these works was not reported. Therefore, in this article, we analyzed the effect of nanofluid stability on boiling heat transfer using nanofluids of varying stability. Nanofluids prepared by dispersing functionalized multi-wall carbon nanotubes in ethanol remained stable even after boiling. We confirmed the stability of these nanofluids by comparing the mean particle size of freshly prepared and boiled samples by dynamic light scattering. Conversely, the aqueous nanofluids prepared using functionalized or non-functionalized nanotubes with and without the aid of surfactants, destabilized instantly when boiled. To test the effect of nanofluid stability on boiling heat transfer, we employed each of these nanofluids, and the base liquids ethanol and water to cool a polished heated copper disc. Interestingly, we found that only stable nanofluids cooled the disc faster compared to the base liquid. Since stable nanofluids were shown to enhance boiling heat transfer, we studied the effect of combining stable nanofluids with micro-nanoscale textured metal surfaces. Femtosecond laser micromachining was used to produce laser induced periodic structures and laser inscribed square pillar structures on copper discs, of which the surface morphology was checked using 3D confocal microscopy. We observed a 59% enhancement in the boiling heat transfer rate when stable ethanol based multi-wall carbon nanotube nanofluids were used to cool discs with laser inscribed square pillar texture. (C) 2018 Elsevier Ltd. All rights reserved.