Boiling regimes at various stages
During the "four cell boil-off" experiment reported in the F&P paper (1), each cell goes through different boiling regimes, according to the electric current and to the (bulk) water temperature. The following jpeg helps to explain these different regimes.
The video still at 3:20:14, taken from the "IMRA time-lapse" video (2), exemplifies 4 different regimes of the cell and the graph on the right, obtained by superimposing the four Figures 6 of paper (1), shows the different condition of each regime:
- Cell 1 has completed its boil-off transient since 3 days and is already cold. There is only a thick layer of residual foam settled on the bottom;
- Cell 2 is shown during the most intense boiling phase. The lower transparent liquid layer is quite small. The cathode is much warmer than the surrounding water and generates a lot of vapor volume that goes through all the upper layers (bubbling water, rising foam and stationary foam on top) eventually escaping the cell and causing the loss of water mass;
- Cell 3 is at about 70°C, but, watching the video, it's easy to see the flux of small bubbles rising in its innermost region, just above the cathode. This indicates that at that time, the cathode is already at a temperature higher than the boiling point. However, contrary to Cell 2, these vapor bubbles don't reach the water surface and condense along their upward path, due to the low temperature of the surrounding water. In fact, the upper part of Cell 3 is as transparent as the upper part of Cell 4;
- Cell 4 is at about 60°C, the thin flux of bubbles which rises the cell is due only to the electrolysis gases.
Beyond these mechanism of water vaporization at the electrode surfaces, there is also the evaporation on the water surface of the cell, but its contribution can be neglected because, at low temperatures, it is very small and, at higher temperatures, it is much smaller than the vaporization on the electrode surfaces.