NUMERICAL SIMULATION OF LIQUID-SOLID SLURRY FLOW USING THE EULERIAN-EULERIAN TWO-FLUID MODEL

Abstract

A numerical study was conducted to assess the performance of a Two-Fluid Model (TFM) developed for gas-solid flow in predicting liquid-solid flow, as well as a TFM specifically modified for liquid-solid flow. The physics involved in gas-solid and liquid-solid flows are intuitively different, and some model terms that can be neglected in a gas-solid formulation turn out to be highly relevant in liquid-solid flow. The difference in these two flows is partly due to the fact that the most important physical properties of the fluid, e.g., density and dynamic viscosity, are much higher in a liquid compared to a gas. In order to investigate the differences between the two base case models, three intermediate models were proposed, and together with the two base case models, assessed in terms of their predictions for an experimental test case. The specific test case was fully developed, turbulent, steady flow of a liquid solid mixture in a vertical pipe. The main differences in the model formulations pertain to the fluid momentum, granular temperature and turbulence kinetic energy transport equations. The other model terms remained similar, i.e., the eddy viscosity constitutive relation, the LRN k-ε closure and the turbulence modulation relations. The present study focused on the predictions for the velocity profile of both the liquid and solid phases, the solids volume fraction profile and budgets of the transport equations for the granular temperature and turbulence kinetic energy. The results obtained were used to identify the model terms that are most significant. These include new formulations for the solids viscosity and granular temperature conductive coefficient, which include the effects of the interstitial fluid effect. The single most important term was the model for the long-range particle fluctuations through the fluid, which played a dominant role in the balance of the turbulence kinetic energy and granular temperature transport equations. The present thesis proposes that this term, which was specifically developed for the case of liquid-solid flow, should be configured as a sink term in the granular temperature equation and a source term in the turbulence kinetic energy equation. With this modification, the numerical predictions were much closer to the experimental data, especially in terms of the solids volume fraction profile in the near-wall region.