Effect of nanoparticles concentration and their sizes on surface tension of nanofluids

Nanofluids, a colloidal mixture consisting of nano-sized particles dispersed in a fluid medium with amended thermo-physical properties play a critical role in the heat transfer performance of a thermal system. Surface tension is the surface energy per unit area or the force per unit length dominates the transportation of the liquid and shows a significant role in heat transfer. However, a few numbers of studies demonstrated about the effect of surface tension of nanofluids. Thus, the present experimental study investigates the effect of nanoparticles concentration as well as the influence of variation of nanoparticles along with their sizes. The nanofluids are prepared by dispersing Al2O3(13nm and 50 nm), TiO2 (21nm) and SiO2 (5 similar to 15nm and 10 similar to 20nm) nanoparticles in Distilled Water (DW). The traditional Du-Nouy ring method was used to measure the value of the surface tension of nanofluids by an automatic surface tensiometer (DCAT 11EC). The results show that the surface tension of the nanofluids increases with increase in concentration and nanoparticle sizes. Besides, TiO2-DW nanofluids exhibit higher surface tension than Al2O3-DW and SiO2-DW nanofluids respectively. All in all, the results indicate surface tension of the nanofluids enhances from 2.62 % to 4.82% in comparison with the base fluids for concentration variation of 0.05 Vol % to 0.25 Vol % at 25 degrees C. (C) 2015 The Authors. Published by Elsevier Ltd.