A study of the effect of nanoparticle concentration on the characteristics of nanofluid sprays

Nanofluids are metallic or nonmetallic, nanometer-sized particles dispersed in liquid. They can be used in various fields to increase heat transfer rates, as the thermal conductivity of nanofluids can be increased significantly. Nanofluids may be used as a good alternative coolant in spray cooling applications. This study conducted experiments to compare spray characteristics, such as droplet diameters and velocities, between water and alumina nanofluid sprays. The mass ratio of alumina nanoparticles was varied from 0.2 to 0.5 weight percentages (wt.%) and the spray injection pressure was varied between 0.2 and 0.3 MPa. The local distributions of droplet sizes and velocities along the spray axial and radial directions were measured by a laser doppler instrument. Generally, the spray characteristics of nanofluid sprays is significantly different from that of water sprays. The average droplet diameters of the fluids tested increased in an approximately linear manner with the increase in the mass ratio of nanoparticles up to 0.4 wt.%, whereas the average droplet velocities decreased. In the case of the nanofluid spray of 0.5 wt.%, the increase in droplet diameters and the decrease in droplet velocities were much more marked, departing from the linear relationship. This unusual behavior could also be observed in the local distributions of droplet diameters and velocities along the axial and radial directions. Further research studies are required to reveal how the addition of nanoparticles affects the atomization mechanism of nanofluids. The difference in the spray characteristics of nanofluid sprays from that of water sprays should be taken into consideration when the cooling effectiveness of nanofluids and water in spray cooling is compared.