Thermofluid characterization of nanofluids in spray cooling

Abstract

The current study addresses a parametric characterization of nanofluid sprays as a way to improve the thermal performance of spray cooling systems. The nanofluids are prepared using as base solution of distilled water with 0.05% (m/m) cetyltrimethylammonium bromide – CTAB in which nanoparticles of alumina and silver are mixed at different concentrations, namely 0.5%, 1% and 2% (m/m). The effect of the shape of the nanoparticles is also considered. These nanofluids are sprayed using a pressure-swirl atomizer and impact, vertically at two different heights, onto an AISI 304 stainless steel foil. This foil is heated by Joule effect, with two imposed currents, delivering 915 and 2100 W/m2. Infrared thermography is used to measure the thermal footprint from which the dissipated heat flux is calculated. Results show that, in steady state operation, the lowest surface temperature is obtained with the 0.5% (m/m) alumina nanofluid, while increasing alumina nanoparticles, concentration increases the radial temperature distributions on the surface. Results also show a mild effect of the shape of the nanoparticles. Hence, lowest surface foil temperatures are achieved with the silver nanofluid with spherical particles, when compared with the same nanofluid with triangular particles. Heat transfer coefficients decreased with increasing thermal conductivity and dynamic viscosity of the nanofluids. On the other hand, a positive correlation is found between the specific heat capacity of the nanofluids and the spray cooling capacity. For the range of experimental conditions covered in this work, nanofluids have proven to increase the thermal performance of the spray.