الفهرس 
CHAPTER 1: INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The pipe sudden expansions are very important devices used to convert kinetic
energy into pressure energy. Sudden expansions are subjected to many applications
such as fluid transportation, combustion chambers used in aero planes, power plants
and engines as well as cyclone separators and dust collectors, etc. The energy losses
due to separation behind the step wall is the main measure of sudden expansion
performance, therefore there is a need to understand the diffusion phenomena within
the sudden expansion. The aim of this thesis is computationally to study the effects of
solid-particles suspended in downward turbulent-air flow through a pipe with sudden
expansion with different parameters. There are different parameters concerning sudden
expansion design (geometric) and working (dynamic and thermal) that affect the
performance of such important flow geometry. Also, the parameters of solid-phase will
be taken into consideration in the present study.
In this thesis, a numerical study has been carried out based on a self-written
code to investigate gas-solid flow in a vertical downward sudden expansion pipe.
Eulerian-Lagrangian approach is used to simulate the two phases. The continuous
phase (gas) is simulated using Eulerian approach by solving Reynolds-Averaged
Navier-Stokes equations (RANS). The finite volume discretization with hybrid scheme
is used to simulate the gas phase which consists of a system of non-linear partial
differential equations. The dispersed phase (solid particles) is simulated using particle
tracking method by solving particle equations (system of non-linear ordinary
differential equations) using 4th order Runge-Kutta method. The pressure-velocity
coupling is achieved using SIMPLE algorithm. Coupling between the two phases is
established by adding particle source terms and void fraction to the calculation of the
continuous phase taking into account the effect of particle-particle collisions (i.e. 4-
way coupling). The lift force, drag force, gravity force, particle dispersion and particlewall
collisions are also considered in the simulation of solid-phase. The used
turbulence model is standard k-ε model to simulate the turbulence behavior. Also,
ii
energy equation is solved to study thermal field in the geometry. The study is carried
out on different geometries of sudden expansion with different area ratios at various
inlet Reynolds numbers and different solid mass loading ratios, while a constant wall
heat flux is considered in the thermal cases.
Comparisons between the results of the simulations and experimental data taken
from previous published papers for hydrodynamic and thermal properties of flow are
done to verify the code. The comparisons indicate good agreement between numerical
and experimental data.
The results indicate that the presence of particles affects strongly the
performance of sudden expansion. The finest particles can improve the performance of
sudden expansion by reducing the loss coefficient. It is noticed that the finest particles
can enter the separation region behind the step so it enlarges the separation length
compared with what is done by the bigger particles. The increasing mass loading ratio
also improve the performance and a bigger separation region is generated. This thesis
also introduces the effect of different parameters with the presence of heat transfer on
the sudden expansion pipe. The heat transfer represented by Nusselt number increases
with increasing Reynolds number in single phase flow, while the presence of particles
in the field will enhance the heat transfer rate in the separation phenomena. In the
detachment region the big size particles enhance the heat transfer better than the finest
one.