Particle-Size Effect of Nanoparticles on the Thermal Performance of Solar Flat Plate Technology

One of the cleanest and most efficient solar collector systems is the flat plate collector, which has applications in hot water production, drying, among others. Flat plate collectors have improved in terms of both their structural configurations and working fluids. Several studies have verified the comparatively higher efficiency of nanofluid-based flat plate collectors, relative to that of water and other thermal oils. Additionally, the influence of several nanofluid synthesis factors, such as volume fraction, pH, type of base fluid, hybridization, surfactants, and sonification, on the performance of these collectors has been highlighted in the literature. However, the effect of nanoparticle size on collector performance has received minimal research interest, despite its significant effect on both the cost of synthesis and the thermophysical properties of nanofluids. The uncertainties regarding the effect of nanoparticle size on thermal collectors have limited their practical applications. This study numerically investigates the effect of the nanoparticle size of silver (Ag) nanofluid with nanoparticle sizes between 20 nm and 100 nm on the performance of flat plate collectors. The effect of nanoparticle size on the mean fluid temperature resulted in a maximum temperature of 45.8 °C for the Ag-100 nm. An increase of 0.25 °C for the Ag-20 nm was recorded, relative to the Ag-100 nm. In addition, the Ag-100 nm was calculated to have resulted in the highest reduction in collector size (18.30%), relative to that of water.