Study of Heating and Evaporation of Rotating Graphene Nanofluid under the Influence of Solar Radiation

Conversion of solar radiation into steam is presently one of the trends in “green” energy (solar thermal energy), ecology, and clean water production. For the first time, a study of the heating and evaporation of a rotating graphene nanofluid under the influence of radiation from a solar simulator was carried out. The influence of various factors on these processes, including the direction of irradiation, graphene concentration, and liquid rotation speed, is considered. It has been shown that the evaporation rate significantly depends on the graphene concentration and the method of irradiation of the samples. When samples are irradiated from the side, as the graphene concentration increases, the average evaporation rate increases and reaches a maximum value and then decreases. When samples are irradiated from above and the liquid–air interface is in direct contact with the incident radiation, only a decrease in the evaporation rate is observed as the graphene concentration increases. In this case, heating of graphene also depends on the method of irradiating the sample. When in direct contact with radiation, graphene is heated to a high temperature, while in the bulk it is heated less efficiently than the base liquid (distilled water). It has been shown that the rate of evaporation from the surface of a rotating graphene nanofluid and the temperature of its volume significantly depend on the rotation speed. Of all the samples studied, a graphene nanofluid with a volume concentration of 0.5% is heated most efficiently. The use of thermal insulation can improve heating by approximately 5%. An analytical calculation of the profile of the interfacial surface is presented and its area is determined at different speeds of rotation of the liquid. Some effects that arise during the rotation of a graphene nanofluid and their influence on the parameters of hydrodynamics and heat and mass transfer, which is important for fundamental and applied energy problems, have been identified.