An Experimental Investigation on Synthesis, Characterization, and Photothermal Conversion Efficiency of Stable Aqueous Nanofluids Containing Multiwalled Carbon Nanotubes for Direct Absorption Solar Collectors

The nanofluids are the potential substitute in solar collectors as working fluids for better photothermal conversion efficiency. The present investigation focuses on the development of aqueous‐based nanofluids comprising multiwalled carbon nanotubes (MWCNTs) with and without surfactants to enhance the capacity of photothermal conversion in direct absorption solar collectors. To improve the stability of the nanofluid, the gum Arabic (GA) and polyvinyl alcohol (PVA) are used as the surfactants. The stable nanofluid was characterized using UV‐visible spectroscopy, zeta potential, fourier‐transform infrared spectroscopy, field emission scanning electron microscopy, and energy dispersive X‐ray spectroscopy (EDS) analysis. The results indicated that the thermal conductivity was enhanced by 94.57% and 91.19% for the MWCNT/GA/deionized (DI) water and MWCNTs/PVA/DI water based nanofluids in presence of surfactants at 90 °C and 0.02 wt%. The presence of surfactant in MWCNTs/DI water nanofluids exhibit excellent stability and enhanced MWCNTs dispersion. In the photothermal response analysis, the highest temperature of 62.8 °C, which is 16 °C higher than the base fluid, is obtained from 0.02wt% MWCNT/GA nanofluid. The highest efficiency of 27.94% is recorded when 0.02wt% MWCNT/GA nanofluid is used, which shows 71.24% enhancement as compared to the DI water after exposure of 30 minutes under solar irradiation. The use of MWCNTs/GA nanofluid as light‐absorbing working fluids in solar collectors is encouraged in the present investigation.