Solar steam generation in fine dispersions of graphite particles

The direct photothermal boiling in suspensions of nano- and microscopic particles finds multiple applications in concentrated solar power: turbine-based combined heat and power (CHP) generation, solar distillation, energy storage, and chemical synthesis. However, the most promising application is solar desalination. There have been multiple studies aimed at the evaporation of suspensions using simulated solar light, but there is neither a theory describing the process nor a well-documented prototype study. This article aims at the development of an experiment and a theory, that describe the photothermal boiling in aqueous suspensions of graphite. We develop a laboratory scale steam-fluid loop with continuous condensation that recycles the water back to the process. We clarify how the concentration and incident radiant heat influence the steam generation. The optimum concentration of graphite particles - 1 wt% - was found experimentally at 17.4 suns. We studied the granulometry of the suspension and dynamics of steam bubbles. We document how the particle size distribution and bubbles evolve in boiling suspension. The theoretical description of the process is based on a heat balance analysis for an individual steam bubble. The developed model is validated against three independent experimental datasets, exhibiting accuracy with the lowest average discrepancy of 10%.