A combined numerical and experimental study on graphene/ionic liquid nanofluid based direct absorption solar collector

• Combined numerical and experimental study on graphene/ionic liquid nanofluid based high temperature receiver.
• Effects of solar concentration, graphene concentration, nanofluid height on receiver efficiency were obtained.
• Receiver efficiency was beyond 0.7 below 700 K.

Novel heat transfer fluids with very low vapor pressure and high thermal stability are highly desirable for both high temperature direct solar collectors and concentrated solar collector. Herein a combined analytical and experimental study has been conducted on high temperature direct solar thermal collectors using graphene/ionic liquid nanofluids as the absorbers. A one-dimensional transient heat transfer model has been used to predict the receiver temperature and efficiency with varying parameters such as solar and graphene concentration and receiver height. The results show that the experimental temperature is in good agreement with numerical results under the same conditions. Based on the model, it is shown that the receiver efficiency increases with the solar concentration and receiver height, but decreases with the graphene concentration. The receiver efficiency could be maintained 0.7 under the conditions of 0.0005 wt% of graphene in 5 cm receiver under 20×1000 W m−2 at 600 K. This work provided an important perspective to the graphene/ionic liquid nanofluids for use as a kind of novel heat transfer fluid in direct solar thermal collectors under concentrated solar incident radiation.