synopsisThe problem of drag reduction in a helically coiled tube is examined experimentally. The general problems involved in the correlation of drag reduction data are analyzed critically, and some important recommendations are made based on the findings of this work. A phenomenological approach is suggested for correlating the drag reduction data. An examination of the straight-tube data from the literature and the coiledtube data obtained in this work shows that for a variety of aqueous polymer solutions the data could be uniquely correlated by the following equation:where fl = reduced friction factor and De' = modified Deborah number.The problem of drag reduction under turbulent flow conditions by the addition of small quantities of high molecular weight polymers has been extensively studied in the literature. The majority of the work has been done in straight tubes, and there is little information in the literature on drag reduction under conditions when the fluids are flowing in flow situations other than straight tubes. Many tentative explanations have been offered to explain the phenomenon of drag reduction but none of them is entirely convincing. Many phenomenological and molecular approaches have been used to correlate the drag reduction data but I I critical analysis of these approaches has not been attempted before.In view of the factors mentioned above, we have undertaken an experimental study of drag reduction in one such interesting situation, namely, in helically coiled tubes. We have critically analyzed the general problem of correlation of drag reduction data and we have proposed a phenomenological approach for correlating such data. We have then shown that such a correlation enables us to correlate the data for different dilute aqueous polymer solutions flowing in a variety of flow situations.

synopsisThe use of a rotating sphere viscometer for the measurement of parameters in the flow curves of inelastic as well as viscoelastic liquids is examined. An experimental investigation of the primary flow around a sphere rotating in Newtonian and viscoelastic liquids is carried out by using a new "three-dimensional particle technique." Currently available theoretical analyses of rotation of a sphere in viscoelastic liquids are shown to be inadequate to describe the experimental primary velocity distribution data. Theoretical results for the primary distribution derived on the basis of a creeping flow of a power law liquid are found to describe the experimental data well. This distribution is then used to derive torque-angular velocity relationships, which are then confirmed experimentally for both inelastic and viscoelastic liquids. The results of this work justify the use of a rotating sphere viscometer as a useful tool for the measurement of parameters of flow curves of inelastic and visccelastic liquids.

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