Two-Fluid Modeling of Dilute and Dense Liquid-Particle Flows
Date
2025-01-14
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Type
Thesis
Degree Level
Masters
Abstract
This thesis explores the use of computational fluid dynamics (CFD) to model multiphase flows. Specifically, a multiphase Eulerian-Eulerian model, referred to as the two-fluid model (TFM), is explored with applications to turbulent liquid-solid vertical pipe and horizontal channel flows. The TFM provides a computationally efficient method to solve multiphase flows, but requires several closures and constitutive relations. The TFM used in this research is implemented in a one-dimensional (1-D) in-house code that uses a low-Reynolds number (LRN) 𝑘 − 𝜀 turbulence model with a volume fraction solver based on the particle-phase radial/transverse momentum balance. The goals of this research were to benchmark the use of the in-house TFM to solve relatively dilute turbulent liquid-solid vertical pipe flows, explore the effects of different turbulence modulation terms, extend the use of the TFM to dense vertical pipe flows and explore the performance of the TFM for horizontal liquid-solid open-channel flows. Within the context of these goals, new particle-phase boundary conditions developed by Schneiderbauer et al. (2012b) were implemented and a particle-phase frictional stress model based on Schneiderbauer et al. (2012a) was introduced.
The benchmarking of the vertical dilute liquid-solid pipe flow showed that the model adequately predicted the fluid-phase mean and fluctuating velocities but underpredicted the particle-phase mean and fluctuating velocities. Of the turbulence modulation models explored, the so-called New model was the only one capable of predicting both turbulence attenuation and turbulence enhancement, depending on the particle diameter. The application of the TFM to dense vertical pipe flows showed that the code can predict 10% bulk volume fractions flows but struggles to predict denser 30% bulk volume fraction flows. The new boundary conditions were successfully implemented, which represents an improvement over the previous heuristic boundary conditions used in the code. The use of the TFM in liquid-solid open-channel flow showed that the model could predict the mixture velocity profiles for neutrally buoyant, small particles, but failed to predict the experimental volume fraction profiles from Wang and Qian (1989). The particle-phase frictional model was implemented for these horizontal flows, but its contribution was limited and confined to the near-wall region.
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Keywords
Multiphase Flow, CFD, Two-Fluid Modeling, Liquid-Particle Flow
Citation
Degree
Master of Science (M.Sc.)
Department
Mechanical Engineering
Program
Mechanical Engineering