Numerical study of unsteady laminar multiphase flow through a rectangular curved duct .

Abstract

Multiphase flows in curved ducts are used in many industrial processes, such as water treatment, oil production, water desalination, refrigeration, air conditioning, and other food systems and material handling processes. Fluid flow in curved ducts differs from straight ducts due to centrifugal force from curvature, which induces secondary vortices and rapid fluid motion. These phenomena, pivotal for heat transfer enhancement, can lead to fluid instability and mixing. This thesis critically assesses current research on secondary flow in rectangular and curved ducts, identifying gaps in understanding and evaluating published numerical and experimental studies. This study introduces a novel design methodology and mesh system to develop a groundbreaking three-dimensional numerical model for multiphase fluid flow in curved ducts, addressing prior constraints. The model utilizes a finite element method employing the Galerkin approach of weighted residuals to solve the governing Navier-Stokes and Level-set equations, effectively capturing the physical phenomena with appropriate boundary conditions. The current study focuses on numerically examining the characteristics of unsteady laminar multiphase flow within a rectangular curved duct. Subsequently, the investigation extends to incorporate the presence of a porous medium and the influence of an external magnetic force. Additionally, heat transfer analysis is conducted to evaluate its impact within the duct. The study investigates the influence of particle concentration, aspect ratio, curvature, Hartmann number, and Dean number on velocity contour, vector plot of flow field, axial velocity and temperature distribution. Additionally, it provides a comparison of two-phase flow among different fluids. The results indicate that as curvature, Dean number, and high-viscosity flow increase, the instability characteristics of the flow decrease. Furthermore, the study presents average velocity magnitudes pertinent to viscosity, porosity, particle concentration, curvature, and Dean number.