Simulation of two-phase bubbly flows: an inert bubble introduced into a hot liquid

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Lai, H., 2003. Simulation of two-phase bubbly flows: an inert bubble introduced into a hot liquid. PhD, Nottingham Trent University.

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Abstract

This thesis numerically studies the behaviour and heat and mass transfer relevant to an inert bubble introduced into a hot liquid. This study is a starting point of investigating the mechanism of transfer phenomena in two-phase bubbly flow based chemical reactors whose production capacity depends on the surface area of the bubbles and on the concentration gradients of species in each phase coupled with the local rate of reaction.

This entirely numerical and theoretical research starts with physical and mathematical modelling. The physical problem is modelled as unsteady conjugate heat and fluid flows around and inside a single rising inert bubble while full Navier-Stokes equations with well-posed boundary conditions are employed as the mathematical description of the problem.

Numerical algorithm for solving the mathematical model has been proposed and developed into Fortran codes. Firstly, a procedure for heat and flows in complex geometries with time-dependent moving boundaries is proposed. This procedure incorporates a multi-block iteration strategy with a moving mesh arrangement and is designed to calculate the heat and flows inside and around a single inert bubble; high order discretisation schemes are introduced and employed to obtain high resolution of the numerical results. Secondly, interfacial treatments are introduced and the algorithm is further developed to calculate gas-liquid interfacial flows in bubbles. Validations are widely carried out by available experiments and benchmark numerical data, robustness and potentials of the numerical algorithm and the codes are well shown.

Steady heat and fluid flows inside and around inert bubbles are carefully studied. Considering the importance of spherical bubble model, interfacial characteristics and flow structures of spherical bubbles are carried out. As the main work, detailed numerical studies are applied to moderately deformed bubbles in the ranges of (Re(2)We)=[o, 200]x[0, 6]. Bubble shape, interfacial characteristics, flow structure, drag coefficient, and heat and mass transfer are carefully analysed to study the mechanism of interfacial transfer phenomena. The effects of bubble wake on the recovery of heat and mass transfer are identified and physically explained.

Based on some supplementations of the numerical procedure, time-accurate simulations on the rising-up of single inert bubbles are carried out to observe the unsteady heat and mass transfer and the relevant mechanisms. Full story of the bubble rising, evolution of bubble shape, development and propagation of temperature and concentration fields are numerically observed and analysed.

Item Type:

Thesis

Creators:

Lai, H.

Date:

2003

ISBN:

9781369324969

Identifiers: