| Summary: | The rheological properties of kaolin suspensions in water have been studied using a capillary tube viscometer. A method has been presented which permitted the selection , of a kaolin-water-glycerol mixture of required rheological properties. The effects of air injection into Newtonian liquids and shear-thinning suspensions have been studied in a horizontal test section of 41.7 mm internal diameter and 4.57 m long. Experimental observations entailed the measurements of flow rates of air and liquid, average pressure drops and the average and the instantaneous values of holdup. Over the range of air and liquid flow rates studied, both the plug (elongated bubble) flow and the slug flow regimes were obtained. For Newtonian liquids a 33-fold range of viscosities could conveniently be obtained; the injection of air resulted always in a monotonic increase in pressure drop whether the flow of liquid was laminar or turbulent. Results could be satisfactorily correlated by the Lockhart-Nartinelli method, incorporating the Chisholm-Sutherland correction factor where necessary. Furthermore, correlations have been developed to estimate the average liquid holdup and the average liquid holdup in the liquid slug and in the liquid film. Using the estimated values from these correlations, it has been shown that the Hubbard-Dukler slug flow model could be used to predict the average pressure drop for Newtonian liquids, initially in both laminar as well as in turbulent flow. The laminar flow of flocculated suspensions could be described adequately by the power law model, and for a range of concentrations of kaolin-water-glycerol, n' varied from 1.0 to 0.14 and K' from 0.02 to 29 Nsn'.m-2. The injection of air into these materials when in laminar flow could result in a substantial pressure drop reduction. A method has been presented to estimate the minimum pressure drop attainable at any flow rate of a liquid of given rheological properties; and also to estimate the corresponding air flow rate needed. Moreover, by modifying the Lockhart-Martinelli parameter X to take account of shear-thinning properties of liquids, it has been possible to use the same correlations as for Newtonian liquids. Hence the Hubbard-Dukler slug flow model could be used to estimate the minimum pressure drop. If the shear-thinning suspensions were initially in turbulent flow, the injection of air always resulted in an increased pressure drop. The average values of liquid holdup and of pressure drop could then be estimated from the correlation which were applicable to the flow of Newtonian liquids.
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