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

• Published in: Energy (Oxford) 2016-01, Vol.94, p.497-507
• Main Authors: Kim, Hyeongmin, Ham, Jeonggyun, Park, Chasik, Cho, Honghyun
• Format: Article
• Language: English
• Subjects: Computational efficiency; Computing time; Energy saving; Nanofluids; Silicon dioxide; Solar collectors; Thermal efficiency; Thermal energy; Titanium dioxide; U-tube solar collector; Working fluids
• ISSN: 0360-5442
• DOI: 10.1016/j.energy.2015.11.021

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. •Thermal performance of an U-tube type solar collector was analyzed theoretically.•MWCNT, Al2O3, CuO, SiO2, and TiO2 nanofluid with 20% PG-water were applied.•Solar collector using 0.2vol%-MWCNT nanofluid showed the highest efficiency.•By using nanofluids, the coal usage can be further reduced by 131.3–39.5 kg for one year when the 50 solar collectors are used.