Synthesis and characterization of silver/water nanofluids

Nanofluid is a new class of fluid that has been reported to exhibit higher thermal conductivity and viscosity compared to the base fluid. This work is concerned about the synthesis and characterization of low concentrations aqueous silver nanofluids (i.e., silver nanoparticles dispersed in distilled water), as well as the effect of concentration and particle size on the effective properties. The synthesis of nanofluids was performed by a new method called high-pressure homogenization in the range of volume fraction 0.1–0.3%. The characterization of thermal conductivity and viscosity was performed by the transient hot wire method and a cone plate viscometer, respectively. The highest increase in the thermal conductivity was found to be 18% at the concentration of 0.3%, with little increase in the effective viscosity. The developed correlations for the effective thermal conductivity of nanofluids under-predicted the experimental results obtained in the present investigation

Experimental investigation of a silver nanoparticle-based direct absorption solar thermal system

A nanoparticle-based direct absorption system provides a promising alternative to conventional solar collectors. This work investigates experimentally the photothermal conversion characteristics of one of the plasmonic nanoparticles, i.e., silver, under realistic conditions. Stable silver nanofluids are formulated through a high-pressure homogenizer and the experiments are conducted under sunlight on a rooftop with tests running continuously for 10 h. The results show that silver particles have excellent photothermal conversion capability even under very low concentrations. Up to 144% enhancement in the stored thermal energy can be obtained at the peak temperature for a particle concentration of 6.5 ppm. The photothermal conversion performance shows a transient behavior and is best achieved at the initial radiation period due to the low heat loss and strong surface plasmon resonance effect of silver nanofluids. Nearly constant initial specific absorption rate (SAR), 0.6 kW/g, is obtained for nanoparticle concentrations up to 6.5 ppm, but it decreases significantly at higher concentrations, which is associated with increased particle–particle interactions