الفهرس 
Classifications of Two Phase FlowOnly 14 pages are availabe for public view
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Abstract
Expanded ducts play a pivotal role in converting kinetic energy into pressure
energy within fluid systems, finding applications in fluid transport, aircraft combustion chambers, power generation, and pollution control. The efficiency of these ducts relies on minimizing energy losses, particularly associated with separation behind their step walls, necessitating a profound understanding of diffusion processes within them. Similarly, diffusers, crucial for transforming kinetic energy into pressure energy, have diverse applications in fluid machinery and aircraft components. The effectiveness of these devices, evaluated by the pressure rise they achieve, underscores the significance of understanding their unique diffusion processes. This study delves into the role of solid-phase elements in gas-solid two-phase flows through sudden expansions and diffusers, contributing valuable insights into these vital components. The thesis employs numerical investigations into gas-solid flow within sudden expansion pipes and diffusers, facilitated by a self-written FORTRAN program. A developed cut cell technique proves effective in assessing diffuser performance, particularly near walls and within separation zones. The numerical approach utilizes the Eulerian-Lagrangian framework to model the two phases. The continuous phase (gas)
is simulated using the Eulerian framework, solving the Reynolds-Averaged NavierStokes equations (RANS). Simultaneously, the dispersed phase (solid) is simulated using the particle tracking method, with particle equations solved via the 4th-order Runge-Kutta method. The SIMPLE algorithm ensures pressure-velocity coupling, incorporating particle source terms and void fractions into the continuous phase
calculation to account for particle-particle collisions (4-way coupling). Lift forces, particle dispersion, and particle-wall collisions are considered in the solid phase simulation. Three turbulence models—the standard k-epsilon model, the standard Chen-Kim model, and the proposed coefficient-enhanced Chen-Kim model—are evaluated to determine the most suitable model. The study began by comparing outcomes from three turbulence models with data from prior research on single and two-phase flows through sudden expansions and diffusers. This analysis identified the most suitable turbulence model. After model selection,
validation continued using the chosen turbulence model for simulating gas-solid twophase flows across various geometries. To showcase the numerical model’s efficacy, a comprehensive comparison between current numerical results and experimental findings was executed. Consistently, strong concurrence between numerical and
experimental datasets was observed. Notably, the Chen-Kim model, enhanced with suggested coefficients, emerged as the top performer in predicting the hydrodynamic field compared to the other two models. Various geometrical configurations of sudden expansions and diffusers, featuring different area ratios (𝐴𝑅 = 2.56 , 3.71, 𝑎𝑛𝑑 7.11) and diffuser cant angles (𝛼 = 3.4, 7, 𝑎𝑛𝑑 10 𝑑𝑒𝑔𝑟𝑒𝑒𝑠), are investigated across a range of inlet Reynolds numbers (𝑅𝑒 = 3 × 104 𝑡𝑜 3 × 105), solid mass loading ratios (𝑀𝑅 = 0.5 𝑡𝑜 1.5), particle materials
(𝜌𝑝 = 800, 2500, 2700, 8940, 𝑎𝑛𝑑 19320 𝑘𝑔/𝑚3), and sizes (𝐷𝑝 = 50 𝑡𝑜 770 𝜇𝑚).
This parametric study investigates the impact of flow and geometrical parameters on gas and particle velocities, gas streamlines, particle trajectories, pressure, skin friction
coefficient, boundary layer development, turbulent kinetic energy development, and loss coefficient.