Pressure drops and flow patterns in sand-mixture pipes V. Matousek * Delft University of Technology, Chair of Dredging Technology, Mekelweg 2, 2628 CD Delft, The Netherlands Accepted 8 November 2001 Abstract The paper discusses a relation between the flow friction and the flow pattern in a pipe transporting a sand–water mixture. The studyisbasedonthelaboratoryexperimentsthatwerecarriedoutina150-mmpipeforflowsofvarioussandfractionsanddifferent flow patterns. Three pipe inclinations (horizontal, vertical and 35° descending pipes) were used to establish different flow patterns. During the tests the flow patterns varied from fully stratified to fully suspended. In the fully stratified flow all particles were transported in a granular bed sliding over the bottom of a pipe or in a shear layer linked to the granular bed (all particles were transported as the contact load). In the fully suspended flow no bed was present in a pipe and all particles were dispersed within a carryingliquid(allparticlesweretransportedasthesuspendedload).Inmanycasestheflowwaspartiallystratified,i.e.aproportion ofsolidparticlesoccupiedagranularbedatthebottomofapipeandtherestoftheparticlesweredispersedwithinacarryingliquid abovethebed.Thetestedsolidswerethreenarrowlygradedfractionsofsand(d 50 ¼ 0:12,0.37and1.85mm)andtwosortsofmixed sand (blended from two narrowly graded fractions: the 0.37-mm sand þ the 0.12-mm sand or the 1.85-mm sand þ the 0.12-mm sand). The distribution of solids across the pipe cross-section was measured to identify the flow pattern. Integral flow parameters (mean mixture velocity, delivered concentration of solids, differential pressure) were measured to determine the flow friction for various flow conditions. The paper presents a survey of selected results from a large database collected during a long measuring campaign. It shows the way the measured solids distributions across a pipe cross-section were analyzed to distinguish between the contact load and the suspended load and compares the frictional pressure drops in mixtures of different flow patterns. The measurements confirmed that flows with a higher degree of flow stratification exhibit considerably higher friction than flows with a lower degree of stratification. For the horizontal flow of the mixture of the volumetric concentration 0.12–0.13 at velocities slightly above the deposition-limit threshold (around 3 m/s) the frictional pressure drop in the 0.12-mm sand mixture was approximately two thirds of that in the 0.38- mm sand mixture and less than one half of that in the 1.85-mm sand mixture. The addition of the 0.12-mm sand (the solids concentration 0.13–0.15) to the mixture of the concentration 0.12–0.13 of either the 0.37-mm sand or the 1.85-mm sand reduced the solids effect on the total frictional pressure drop to approximately one half at velocities slightly above the deposition-limit threshold. The vertical flows exhibit slightly less solids friction than the horizontal non-stratified flows. For the mixtures of concentration 0.26 of both the 0.37-mm sand and the mixed sand blended of the 0.37-mm sand and the 0.12-mm sand, the solids effect on the total frictionalpressuredropinverticalflowwasapproximatelytwothirdsofthatinanon-stratifiedhorizontalflow.Acomparisonofthe experimental data with the predictive models for the frictional pressure drop suggests that more reliable models are available for stratified flows than for non-stratified flows. Ó 2002 Elsevier Science Inc. All rights reserved. Keywords: Slurry flow; Concentration distribution; Flow friction 1. Introduction It is well known that friction losses in pipeline flows of sand–water mixtures are strongly dependent on the flow pattern developed in a pipeline. Sand–water mix- tures are settling mixtures. If the mean velocity of a mixture in a horizontal pipe is low they form a granular bed at the bottom of a pipe. The bed is stationary at velocities below the deposition-limit threshold and slides over the pipeline wall at velocities above this threshold. In principle, the velocity range within which the contact bed occurs in the mixture flow depends on the pipe size, the particle size and the mean concentration of solids in a mixture flow. A contact bed is a major contributor Experimental Thermal and Fluid Science 26 (2002) 693–702 www.elsevier.com/locate/etfs * Tel.: +31-15-278-3717; fax: +31-15-278-2492. E-mail address: v.matousek@wbmt.tudelft.nl (V. Matousek). 0894-1777/02/$ - see front matter Ó 2002 Elsevier Science Inc. All rights reserved. PII:S0894-1777(02)00176-0