DYNAMIC MODELING OF GAS HOLD-UP IN DIFFERENT ELECTROLYTE SYSTEMS

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 epsilon(u(g)(0)) depends on the type of electrolyte and its concentrations as well as o n the type of gas. Using an ultrasonic Doppler velocimeter, bubble ris e velocities were investigated. It was observed that the single bubble rise velocity in electrolyte solutions depended strongly on the conce ntration. A model, developed to take into account the impediment to co alescence by electrolytes, was used to evaluate the dependence of gas hold-up on electrolyte concentration. An almost linear correlation bet ween the system specific parameter, epsilon(max), of this model and th e ionic strength was found. However, this correlation is not too accur ate and can only be seen as a rough approximation. Experimental result s indicate that another mechanism is responsible for the dependence of the gas hold-up on electrolyte concentration. Thus, a new model was d erived, which incorporated results of measurements of bubble rise velo cities. This model was also applied to describe the gas hold-up in dif ferent electrolyte solutions as a function of gas flow rate. It also i ncludes a system-specific parameter. The dependence of this parameter on the concentration of electrolytes was found to be in accordance wit h current theories on the bubble coalescence.