Experimental investigation on photothermal conversion performance of MWCNT-DW/EG nanofluids for low-temperature direct absorption solar thermal energy systems

Solar collector is the core equipment of solar solar thermal utilization system, but its efficiency of solar thermal conversion is low, and it has not yet met the needs of practical applications.Direct absorption solar collector (DASC) serves as a promising technology to harvest solar energy, but the performance of DASCs is largely affected by the working liquid. In this paper, the effects of MWCNT-DW/EG nanofluid mass fraction, pH value, mass velocity and liquid level height on the stability, optical properties, thermal conductivity and the perfor-mance of direct absorption solar thermal conversion were investigated. The potential of MWCNT nanofluid for direct absorption solar collector was evaluated comprehensively. The results showed that the 0.01 wt% MWCNT-DW/EG nanofluid with pH of 7 can achieve the best photothermal conversion that increased up to 38.5 % compared to the base fluid, and the efficiency of DASC was significantly higher than that of evacuated tube solar collector with selected-coating after being exposed under a solar intensity of 700 W/m2 for 2400 s. This study provides scientific data and important reference for the numerical simulation and practical application of the direct suction solar collector.