| Summary: | Bibliography: v. 1, p. 392-418. === Mixed regime slurries are those slurries comprised of broad particle size distributions. Slurries of this type with volume concentration up to 50 (relative density of approximately 1.8) are considered.. An analytical model has been developed for such slurries. The inputs to the model are mean mixture flow rate, delivered. concentration and the particle and pipeline characteristics.. In order to calculate in situ concentration, the concentration distribution is found by using a diffusion model. A logarithmic velocity distribution is also required and is used to ascribe velocity values to volume elements in a concentric computational grid. Calculated values of mean mixture flow rate and delivered concentration are compared to the input values and an iterative procedure is employed to ensure equality with a result being the computation of in situ concentration. The model is applicable over the complete range of flow regimes including stationary bed, sliding bed and suspended flow. The particular regime prevalent for the input values will be ascertained by the model aid the energy gradient calculated. The model is compared to 3 existing correlations in the literature, for mixed regime flow, using 1345 data points collected at the University of Cape Town test facility and 1630 data points from other institutions. The test facility used comprises two systems each with two pipelines and separate centrifugal pumps. The four pipelines range from 50mm inside
diameter to 140mm inside diameter. A data acquisition system continuously monitors pressures, velocity and temperature. Mixture concentration and velocity are checked using a weigh tank which is filled over a time interval by diverting the slurry flow. Pressures are checked with water manometers. The data acquisition system is interfaced to a microcomputer that calculates required. values and outputs tables and graphs of measured values. Detailed observations of the flow conditions are made through clear viewing sections in each pipeline.
A qualitative investigation of periodic flow phenomena observed is presented. These are a result of sliding bed flow and include dunes, waves and slugs. A two-fluid model is proposed and the mechanisms whereby these structures form, grow and eventually disperse is discussed.
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