Dynamic modelling of gas hold-up in different electrolyte systems

Abstract

In measurements of gas hold-up of oxygen and hydrogen as a function of the gas flow rate it was found that the gas hold-up epsiv(ug0) depends on the type of electrolyte and its concentrations as well as on the type of gas. Using an ultrasonic Doppler velocimeter, bubble rise velocities were investigated. It was observed that the single bubble rise velocity in electrolyte solutions depended strongly on the concentration. A model, developed to take into account the impediment to coalescence by electrolytes, was used to evaluate the dependence of gas hold-up on electrolyte concentration. An almost linear correlation between the system specific parameter, epsivmax, of this model and the ionic strength was found. However, this correlation is not too accurate and can only be seen as a rough approximation. Experimental results indicate that another mechanism is responsible for the dependence of the gas hold-up on electrolyte concentration. Thus, a new model was derived, which incorporated results of measurements of bubble rise velocities. This model was also applied to describe the gas hold-up in different electrolyte solutions as a function of gas flow rate. It also includes a system-specific parameter. The dependence of this parameter on the concentration of electrolytes was found to be in accordance with current theories on the bubble coalescence.