▎ 摘　　要

In this paper, the optical absorption properties and photo-thermal conversion characteristics of GOwater nanofluids were experimentally studied and compared. With the increase of GO mass fraction or the decrease of GO sheet size, the optical absorption capacity of nanofluids can be enhanced, and a thin layer of nanofluid can absorb most of the solar irradiation. As for a direct absorption solar collector (DASC), the temperature rise increased with the irradiation angle at the reverse-irradiation mode because of the natural convection induced temperature uniformity improvement. There existed optimal GO concentrations with respect to the maximum temperature rises of GO nanofluids, and the optimal value is GO sheet size dependent. For GO sheet sizes of 50-200 nm, 200-500 nm and >500 nm, the optimal mass fractions are 150,180 and 220 ppm, respectively, and the corresponding temperature rises were increased by 9.2 degrees C (28.2%), 7.9 degrees C (24.1%), and 6.9 degrees C (21.0%) as compared with that of water at the reverse irradiation angle of 45 degrees. A 3D numerical simulation was performed to understand the irradiation angle induced natural convection contribution to the photo-thermal conversion performance, and an agreement was achieved with the experiment.