(98d) Performance Characterization of the GS-4 Gas Induction Impeller

The GS-4 impeller is a novel gas induction impeller that is differentiated by its large openings for gas flow and generation of an axial flow pattern. This impeller is characterized based on the power number, pressure coefficient, and modeling of the induced gas flow rate. The power number at ungassed conditions is independent of impeller size and submergence, but is higher when up-pumping than down-pumping. This parameter decreases as gas is induced, and is modeled using the relative power number as a function of the relative speed. The pressure coefficient is examined using two approaches, one using speeds below the onset of induction and the other using the critical speed. Comparison of these methods shows that the pressure coefficient is more accurately determined independently of the minimum induction speed, and that there is a pressure loss encountered within the impeller as gas is forced outward from the center. This information is used to relate the available pressure difference to the gas flow rate. This relationship is affected by impeller diameter, with larger impellers inducing a higher flow rate than smaller impellers for a given pressure difference. The accuracy of the model is improved by assuming that the gas flow rate is also a function of the gas-liquid contact area within the impeller. The gas flow rate is also analyzed using a model that relates induction to an injection process, however it is difficult to evaluate the validity of this model due to the pressure drop introduced by the gas flow rate measurement method.