Two-phase bubble flow and convective mass transfer in water splitting processes

When hydrogen or oxygen is produced from water splitting by electrolysis, thermochemical cycles or solar-based photocatalytic methods, bubble flow and vapor transfer into the gas phase occur during phase transition. This undesirable vapor transfer requires the use of more energy input to compensate for the evaporation heat requirement as well as for subsequent gas purification in the downstream unit. In this paper, both experimental and modeling studies are performed to examine the dynamics of bubble flows and kinetics of water vapor transfer, particularly related to processes of hydrogen production. Experimental data are obtained using an advanced laser-based shadow imaging system and on-line vapor monitoring system. The bubble dynamics and water vapor transfer kinetics are modeled with non-dimensional parameters involving the bubble diameter, velocity and trajectories so that the water vapor transfer rate can be quantified under different operating conditions for various hydrogen production methods. Also, a predictive model is developed to simulate the physical processes of bubble transport in a vertical liquid column, as it occurs in water splitting processes such as oxygen generation in the thermochemical copper–chlorine cycle, as well as hydrogen generation in electrolytic and photocatalytic processes.