An experimental and theoretical study of the hydraulic transport of coarse solids in both water and shear-thinning fluids has been carried out with a view to developing an improved procedure for the prediction of pressure drop for flow in horizontal pipes. An examination of the experimental results and correlations used by previous workers has shown that none of the presently available methods of calculating the pressure drop is capable of forming a reliable basis for a design procedure. Results obtained by different workers under seemingly similar experimental conditions can yield pressure drops differing by as much as 11-fold. It is suggested that two important factors have not been adequately taken into account in the past. The first is that cognisance has not been taken of the fact that the in-line concentration of solids (which determines the flow conditions within the pipe) may be considerably different from the concentration in the mixture discharged from the pipe because of the existence of a 'slip' between the liquid and the particles. Secondly, very few workers have measured the coefficient of friction between the solid particles and the pipe wall, a variable which has a very strong influence on the pressure drop when bed formation occurs. In the experimental programme during which suspensions were transported in a recirculating loop consisting of 38 mm diameter piping, measurements were made of in-line concentrations and of mean liquid velocities within the pipe. In addition, off-line measurements of solids-wall coefficients of friction were made. The experimental results were interpreted using a simplified form of the 'two-layer' model, in which it was assumed that all particles were conveyed in the bed-layer. By use of the conclusion from the experimental work that the slip velocity is close to the terminal settling velocity of the particles, it has not been necessary to make any assumption concerning the interfacial shear between the surface of the bed and the liquid in the upper part of the pipe. The model has been found to predict results of this present study to within ±15%. Comparison with the results of other investigators has been limited because rarely have they measured the coefficient of solids friction. An empirical correlation has been developed for transport in shear-thinning liquids which predicts results for a wide range of data to within ±22%. In addition, a proportion of these results have been interpreted in terms of the proposed model.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:638540 |
| Date | January 1991 |
| Creators | Pirie, R. L. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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