Nanofluid sprays for cooling applications [article]

M. Malý
2018
Introduction Spray cooling is among the most popular liquid cooling strategies, given the high heat transfer coefficients that can be delivered [1] . However, increasingly demanding heat loads in applications such as electronics cooling have pushed researchers to further enhance the heat transfer processes, by altering the surfaces and/or the fluids e.g. [2] [3] [4] . Fluids with nanoparticles are pointed to have great potential to improve heat transfer processes, given their potentially higher
more » ... potentially higher thermal properties. However, increasing the concentration of the nanoparticles may alter significantly other physical properties such as the viscosity, which affect the fluid flow and may eventually reverse any advantage of adding the nanoparticles. Furthermore, while most authors have focused simply on the effect of the nanoparticles on the bulk properties of the fluid, studies on the wettability and on the interaction effects of the particles on the surfaces and on droplet-droplet interactions is scarcely reported. The actual effects of adding nanoparticles in the fluid flow characteristics and, particularly in the mechanisms of atomization, have also been drawn to a secondary plane. In this context, the present work focuses on the effect of nanofluid preparation, particularly on the effect of the nanoparticles concentration, on the local physical properties of the resulting fluid and their consequent effect on the atomization characteristics (droplet size, velocity distribution, spray angle, etc) using nanofluids. The results are discussed focusing on how the spray characteristics affect the use of the resulting spray for cooling purposes. Nanoparticles of alumina (Al2O3) and Zinc Oxide (ZnO) are mixed in water-based solutions, for concentrations varying between 0.5% and 2% wt for alumina and between 0.01% and 0.1% wt for the zinc oxide particles. CuO (0.1% wt) and FeCl2.4H2O (0.1% wt) were also used to infer on the effect of the nature (material) of the particles in the physicochemical properties of the resulting solutions. High-speed imaging is combined with Phase Doppler Anemometry and Laser Scanning Confocal Microscopy to fully characterize the nanofluids properties and the spray characteristics. The results show that liquid viscosity is an important parameter in predetermining the spray characteristics of the nanofluids, as it affects the primary breakup. However, only a minor increase is observed in the nanofluids viscosity, mainly for higher concentrations of alumina. This variation in the viscosity was observed to slightly affect droplet size distribution and to cause a small decrease in the cone angle of the spray. Hence, for the range of nanoparticles nature and concentration covered here, there is a positive balance in the use of the nanoparticles, increasing the thermal properties without a significant deterioration of other fluid properties such as viscosity, or spray dynamics.
doi:10.6092/dipsi2018_pp17-20 fatcat:wm3crptt4fcrzfxe6yrtqhe6cq