Scale Effects on the Hydrodynamics of Bubble Column


The main object of this study is to investigate the influence of the columngeometric and operating variables ( i.e., column diameter, superficial gas velocityand liquid viscosity) on the hydrodynamic parameter ( i.e. , gas holdup, bubbledynamics and liquid phase axial dispersion coefficient ). The experimental dataobtained showed that the gas holdup increases linearly with superficial gasvelocity at both homogeneous and heterogeneous regimes but the rate ofincreasing is slower at the heterogeneous one. The bubble rise velocity was foundto decrease with increasing superficial gas velocity until a transition point wasreached and after that the relationship was linearly increasing. It was observedthat with an increase in liquid phase viscosity and increase in column diameters, adecrease in gas holdup and an increase in bubble size were obtained. It wasobserved that increasing axial position led to an increase in bubble diameter and adecrease in bubble rise velocity. Axial dispersion coefficient which is measuredby tracer response technique was found to increase with gas superficial velocity,increases with column diameter, increases with axial position and decreases withliquid viscosity. This work also presents a theoretical analysis that is used tocalculate the axial dispersion coefficient. The measured axial dispersioncoefficient was generally consistent with the predictions of the well establishedcorrelations from the literature. The validity of the model was settled bycomparing its predication with the objective function of the well-Known empiricalcorrelation formulated by ( Hikita and Kikukawa , 1974) .The comparison showsthat the present model is statistically significant at a 95% confidence level byusing goodness – of – fit test .Also a statstical analysis was performed to get a general correlation for the gasholdup (εg) as a function of the parameters studied:= 0.15325 Fr 0.29617 Ga 0.09223 Bo -0.0424 g eWhere the correlation coafficient ( R ) was equal to ( 0.957) and the absoluteerror (3.5%).