A model of bubble coalescence in the presence of a nonionic surfactant with a low bubble approach velocity

A bubble coalescence model for a solution with a nonionic surfactant and with a small bubble approach velocity was developed, in which the mechanism of how coalescence is hindered by Marangoni stress was quantitatively analyzed. The bubble coalescence time calculated for ethanol-water and MIBC-water systems were in good agreement with experimental data. At low surfactant concentrations, the Marangoni stress and bubble coalescence time increased with bulk concentration increase. Conversely, in the high concentration range, the Marangoni stress and coalescence time decreased with bulk concentration. Numerical results showed that the nonlinear relationship between coalescence time and surfactant concentration is determined by the mass transport flux between the film and its interface, which tends to diminish the spatial concentration variation of the interface, i.e., it acts as a “damper”. This damping effect increases with increased surfactant concentration, therefore decreasing the coalescence time at high concentrations.

The Reactant Concentration Simulation at Catalyst Membrane Interface of a MICRO PEM Fuel Cell

Modeling is increasingly widely used to optimization, improvement and cost reduction efforts of the fuel cell technology. Although there are many computational models in literature that describe the behavior of Polymer Electrolyte Membrane (PEM) fuel cell, there is a only few models that simulates the catalyst surface concentration of reactant gases at the catalyst-membrane layer interface. A modeling of a PEM fuel cell is presented to determine both the bulk reactant concentrations and the catalyst surface concentrations at the catalyst layer-membrane layer interface. The results suggest that the reactant deficiencies experienced at high current densities are localized to the catalyst surface. However, the bulk concentration of reactant is not zero, and, in most cases, the bulk concentration of the reactant gases is significantly greater than zero. In actuality, it is the catalyst surface, which is being depleted of reactant, and, at the limiting current density, the surface concentrations of reactant gases are zero. This treatment develops explicitly link between the fuel cell overpotentials and the movement of reactants. DOI: http://dx.doi.org/10.3126/jie.v9i1.10662Journal of the Institute of Engineering Vol. 9, No. 1, pp. 1–17