Hybrid Nanofluid in a Direct Absorption Solar Collector: Magnetite vs. Carbon Nanotubes Compete for Thermal Performance
Pavel G. Struchalin, D. M. Kuzmenkov, Vladimir S. Yunin, Xinzhi Wang, Yurong He, Boris V. Balakin
Abstract
The paper presents the experimental measurements of thermal efficiency of a tubular direct absorption solar collector (DASC) with a hybrid nanofluid based on magnetite (Fe3O4) and multi-walled carbon nanotubes (MWCNT). The volumetric concentration of Fe3O4 and MWCNT was 0.0053% and 0.0045%, respectively. The experiments were carried out for the flow rates of 2–10 L/min and a temperature difference up to 20 ∘C between the environment and the DASC. The performance of the DASC with a hybrid nanofluid was in the range of 52.3–69.4%, which was just beyond the performance of the collector with surface absorption. It was also found that using a MWCNT-based nanofluid with an equivalent total volumetric concentration of particles (0.0091%), the efficiency was 8.3–31.5% higher than for the cases with the hybrid nanofluid.