Heat transfer performance of silver/water nanofluid in a solar flat-plate collector

Abstract

An experimental study is carried out to investigate the heat transfer characteristics of silver/water nanofluid in a solar flatplate collector. The solar radiation heat flux varies between 800 W/m2and 1000W/m2, and the particle concentration varies between 0.01%, 0.03%, and 0.04%. The fluid Reynolds number varies from 5000 to 25000. The influence of radiation heat flux, mass flow rate of nanofluid, inlet temperature into the solar collector, and volume concentration of the particle on the convective heat transfer coefficient and the collector efficiency are studied. Both parameters increase with increase in the particle volume concentration and flow rate. The maximum percentage increase obtained in the convective heat transfer coefficient is 18.4% for the 0.04% volume concentration at a Reynolds number of 25000. An increase in the performance of nanofluid is also witnessed when compared to the base fluid, which has a strong dependency on volume concentration and mass flow rate. MgO. The nanofluid achieved a 3°C temperature difference during the daytime peak solar radiation compared with the base fluids. With a concentration of 0.2% ZnO, a temperature difference of 2.55°C for daytime and 1°C for nighttime was reached, and this was determined to be the most attractive option for solar energy utilization. Yousefi et al. [15] witnessed a 28% performance improvement in a flat-plate collector when it was operated with water-Al2O nanofluids. Tyagi [16] theoretically compared the conventional flat-plate collector with a direct absorption solar collector (DAC) and observed the former to be 10% more efficient. Otanicar [17] studied the conomic and environmental influences of using nanofluids to enhance solar collector efficiency with conventional solar collectors. Dongxiao et al. [18] presented excellent photothermal properties of carbon-black aqueous nanofluids at highvolume fractions. Further work on nanofluids’ application to direct solar absorption has been carried out by Lijuan Mu [19] using a custom-made direct solar absorber. The radiative properties of several nanofluids are tested for the highest temperature difference across the heat exchangers. Based on the above-mentioned review of the literature, it has been clearly observed that most of the previous studies on solar flat-plate collectors were conducted using metal oxide nanoparticles in relatively high concentrations. These high concentrations of metal oxide nanoparticles cause a higher pressure drop that then requires a higher pumping power. Since a limited number of studies exists in the literature with respect to pure metal nanoparticles, it is recommended to study the heat transfer characteristics of pure metal nanoparticles with relatively low concentrations (<1%) by volume and high thermal conductivity compared with metal oxides. Therefore, in the present study, the efficiency of a solar flat-plate collector is studied with a low particle volume concentration of less than 0.04% silver-water nanofluid. These experiments are conducted for a solar radiation flux ranging from 800 W/m2 to 1000 W/m2, and the Reynolds number varying from 5000 to 25000. The effect of radiative heat flux, mass flow rate, inlet temperature, and volume concentration on the convective heat transfer coefficient and the collector efficiency are studied. The tailormade setup for a collector area is 2.4m2 and the collector plate is made of nine parallel copper strips