Particle Distribution Studies in Highly Concentrated Solid-Liquid Flows in Pipe using the Mixture Model

摘要

The hydraulic conveying of solid-liquid concentrated suspensions in pipelines corresponds to complex flows where particles with different sizes, concentrations and flow velocities exhibit different flow regimens. Predicting their behavior is fundamental for the adequate design of pumping equipment and flow rigs. In traditional numerical approaches the turbulence production is assumed to be directly dependent on the increase of the particle size; this contradicts data from the literature where small particles cause an augmentation of turbulence and medium size particles attenuate turbulence. Also, in the traditional approach the same drag correlation is assumed to account for particle-fluid interaction in different flow regimes, which, in the case of turbulence augmentation and attenuation can differ considerably. In the present work numerical studies were conducted to simulate highly concentrated flows of settling medium sized particles using a Mixture Model, incorporating a Low Reynolds turbulence closure and a Schiller-Naumann drag correlation to depict the flow of concentrated solid-liquid suspensions. Since not all particle distributions were accurately portrayed, different drag correlations were implemented to provide a more adequate representation of the relative velocity between phases and particle distributions. Amongst the drag correlations implemented the Schiller & Naumann showed the best agreement for the highest particle concentrations at intermediate velocities, whilst the Haider & Levenspiel displayed the best fit with the experimental data for the highest flow velocities and particle concentrations. The Gidaspow-Schiller-Naumann drag correlation was more adequate for low flow velocities and with intermediate particle concentrations. With this work it is shown that using the same drag correlation for the numerical description of experimental data for highly concentrated settling solid-liquid flows does not adequately reproduce the different flow regimes.