Effect of the collision medium size on thermal performance of silver nanoparticles based aqueous nanofluids

The present paper describes an influence of different ball sizes (1 mm, 3 mm and 5 mm) of the planetary ball milling machine on the thermal conductivity characteristics of silver-based aqueous nanofluids. Nano-metric silver dispersed water based nanofluids with various loadings (1 wt%, 2 wt% and 3 wt%) have been prepared by a single-step approach. It has been observed that the ground silver nanoparticles suspended in conventional fluids have superior thermal conductivity performance mainly due to flattened particles and/or increased aspect ratio. The silver particles present in colloidal phase have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible spectroscopy, particle sizing system (PSS) and zeta potential measurements. The stability as well as thermal conductivity of these nanofluids have been measured at wavelength ranging from 300 to 800 nm and at temperature ranging 20–40 °C, respectively. As a result, the silver nanoparticles ground by 1 mm ball size that dispersed in aqueous solution (1 wt%) is showed highest thermal conductivity (621 W/mk) which was greater than that of the nanofluids prepared by other conditions, at a temperature of 40 °C. A significant trends in the thermal conductivity of nanofluids are attributed to several specific reasons which have been discussed in this article.