Abstract
The contributions of pressure drop due to wall frictional losses to the total gas holdup of two-phase viscous non-Newtonian systems were experimentally investigated using a 150 dm3 circulating bubble column. The column had a downcomer-to-riser cross-sectional area ratio of 0.54 and a dispersion height of 2.5 m. Aqueous solutions of xanthan gum and carboxymethyl cellulose were used to simulate a wide range of rheological properties. The average wall shear stress was estimated from Al-Masry's (1999) correlation for the average wall shear rate in external loop airlift reactors. Pressure drop due to wall shear stress was found significantly contributed by 10–70 % to the total gas holdup. This contribution has always been ignored in the data presented in the literature due to the absence of reliable and simple correlations for the average shear rate and shear stress. Corrections to gas holdup were found necessary for non-Newtonian solutions with concentrations of ≥ 0.5 wt/wt.-%.
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