Analysis of Early Film Incipience in Surfactant-Aided Electrolysis and Pool Boiling Systems

Abstract Surfactant-aided electrolysis and pool boiling systems typically exhibit premature film formation, which reduces the critical current density (CCD) and critical heat flux (CHF), respectively. Unlike the conventional Helmholtz instability, film incipience in these systems was previously formulated by equating the gas/vapor generation rate with the non-coalesced bubble advection rate from the surface. This study proposes new correlations for CCD and CHF, which address the limitations of previous studies that neglected bubble-bubble interactions and considered the drag coefficient independent of bubble Reynolds number. Presently, the drag coefficient is calculated using the drag law for a spherical bubble swarm with appropriate bubble diameters and Reynolds numbers (Re) before film formation. Correlations based on nonlinear solutions of Re and bubble diameter from experimental data are arrived at, which state that CHF is proportional to the square root of bubble diameter (<10% error), and CCD is proportional to bubble diameter to the power of 1.21 (<5% error). At higher surfactant concentrations, the accuracy of the proposed correlations improves because foaming primarily influences the film incipience phenomenon, rather than conventional bubble column instability. Overall, the proposed correlations in the present study elucidate the physics of film formation in surfactant based electrolysis and pool boiling systems.