Improve the performance of solar thermal collectors by varying the concentration and nanoparticles diameter of silicon dioxide

Abstract

Abstract The influence of different concentrations and nanoparticles’ diameter of silicon dioxide nanoparticles on the Nusselt number enhancement ratio and friction factor for solar thermal collector (STC) was examined numerically. The CFD model was designed to show the influence of the flow of water/SiO2 and pure water inside the pipe on the enhancement of the performance of the STC. Different concentrations of SiO2 nanoparticles are used (ϕ = 1–4%) with several nanoparticle diameters (dp = 20–50 nm). The water/SiO2 and pure water flow under different Reynolds numbers ranging from 5,000 to 30,000. The average Nusselt numbers Nuavg improved by increasing the Reynolds numbers for both fluids. The Nuavg increases with the increase in the concentration of SiO2 nanoparticles. The water/SiO2 with nanoparticle concentration of (ϕ = 5%) and nanoparticle diameter of (dp = 20 nm) has the highest Nusselt number. The Nuavg enhances 25% with water/SiO2 nanofluid flow at Re = 5,000 and 15% flow at Re = 30,000. It is noted that the skin friction factor decreases with the increase in the Reynolds number for both fluids. Water/SiO2 nanofluid has a higher skin friction factor than pure water. The Nuavg improved by 31% at the lowest Reynolds number by using water/SiO2 nanofluid as the working fluid with a change in the concentration of SiO2 nanoparticles from (ϕ = 1%) to (ϕ = 4%) and improved by 42% at the highest Reynolds number of 30,000. The decrease in the nanoparticle diameter led to an increase in the Nusselt number across all Reynolds numbers. The lowest size SiO2 nanoparticles (dp = 20 nm) provides the highest Nusselt number. The lowest size SiO2 nanoparticles (dp = 20 nm) provide the highest ratio of enhancement for the Nusselt number in STC. This investigation has confirmed that the flow of water/SiO2 with AL2O3 nanoparticles of 5% (diameter of 20 nm) has a significant influence on heat transfer enhancement to improve the thermal efficiency of STC.