Experimental Investigation of Phase Change Phenomena in Nanofluids

Thermophysical properties of water like the thermal conductivity, viscosity and the surface tension are observed to change by the addition of nanoparticles. The nature of the variation of these properties with the addition of nanoparticles is a topic of increasing research interest. Rate of evaporation at a liquid surface is affected by various factors, among which the surface tension is the most predominant, and inversely affects the rate of evaporation. The introduction of nano particles into a base fluid obviously makes changes in surface geometry, which in turns alters the surface tension and hence the rate of evaporation. The present experimental study deals with the evaporation of nanofluids, obtained by suspending metal oxide nanoparticles in water. The rate of evaporation was determined by precise measurement of the rate of loss of weight of the nanofluid upon heating, keeping other parameters constant. Experiments with pure water and suspension of aluminum oxide nanoparticles showed that the rate of evaporation of the nanofluid is less compared to that of water, though a definite trend in the variation of the rate of evaporation with respect to the dosing level of nanoparticles was not found to exist. The surface tension is measured using the capillary rise method, which was observed to increase with nanoparticle addition without showing any clear functional relation with the nanoparticle dosing level. Distillation of nanofluids using standard apparatus also indicated a decrease in the evaporation rate with the addition of nanoparticles to the base fluid.