Theoretical investigation of the efficiency of a U-tube solar collector using various nanofluids

Using thermal energy balance, this paper analyzes and investigates the thermal performance of a U-tube solar collector whose temperature thermal energy is high due to solar radiation. A working fluid of 20% PG (propylene glycol)-water is used. Solar collector efficiency was calculated and energy savings predicted for various nanofluids, such as MWCNT, Al2O3, CuO, SiO2, and TiO2. As a result, thermal conductivity increased as the concentration of nanofluid increased. Solar collector efficiency increased in the following order from greatest to least: MWCNT, CuO, Al2O3, TiO2, and SiO2 nanofluids. When the thermal loss value ((Ti−Ta)/G) was equal to 0, the solar collector using 0.2vol% MWCNT nanofluid showed the greatest efficiency (62.8%, a 10.5% improvement compared to 20% PG-water). By dispersing nanoparticles in the working fluid, the coal usage could be further reduced by approximately 39.5-131.3 kg per year when 50 solar collectors are used. Therefore, CO2 generation could be reduced by 103.8-345.3 kg and SO2 generation by 0.4-1.1 kg per year, compared to solar collectors using a base working fluid of 20% PG-water. These findings contribute to knowledge of solar energy technology, which has the potential to reduce electricity and energy consumption world-wide.