الفهرس 
LITERATURE REVIEWOnly 14 pages are availabe for public view
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Abstract
ABSTRACT
The main objective of the present work is to predict the flow properties of an evaporating spray
injected into a heated air stream flowing in an annulus in a pipe with a sudden expansion ratio of
3. The spray is generated by a hollow-cone atomizer, with isopropyl alcohol as a liquid of high
evaporation rate. This work finds its practical importance in many engineering areas such as gas
turbines, sprays and drying processes.
The effect of two-way coupling on both the mean and fluctuating levels is investigated. The mean
interactions include the mass, momentum, and energy transfer between the carrier phase and the
dispersed phase. On the turbulence level, the interaction is caused by the inability of- the
droplets to follow the carrier phase turbulence eddies.
The numerical study presented in this thesis is performed using the widely used computer program
”KIVA -Il code”. In this code a finite volume discretization scheme and an iterative procedure
based on the SIMPLE algorithm are adopted. The governing equations are formulated using an
Eulerian/Lagrangian approach. It is assumed that no droplet coalescence or breaku p occurs. This
implies that the droplets are sufficiently dispersed so that the droplet collisions are infrequent.
The evaporati ng spray is assumed dilute because of the small mass-loading ratio of the liquid to
air.
The Eulerian model was adopted for the carrier phase where the conservation equations of mass,
momentum and energy were formulated in steady, axisymmetric cylindrical coordinates. The turbulence
model used is k-e model. The source terms in the turbulence kinetic energy (k) and its dissipation
rate (e) equations are changed to include the droplet volume fraction and time scales characterizi
ng the droplet response and large-scale turbulent motion.
The droplet phase was treated by the Stochast ic Lagrangian approach, where a large number of
droplet parcels representing a number of real droplets with the same
properties were traced through the flow field. The droplet parcels were traced through the flow
field by solving a set of ord inary differential equations for the droplet location, diameter,
velocity components, and temperature. Forces due to pressure gradient in the flow, added mass
force and Basset history force are negligible since a large density
ratio was considered.
The source terms in the gas phase equations for mass, momentum, energy and K- turbulence model were
evaluated by averaging a number of droplet trajectories. The calculation of the source terms
was based on a modified PSI-CELL approach
introduced by Crowe et al. (1977).
The predictions provide the radial distributions of the axial and radial droplet velocit ies,
Sauter mean diameter and droplet mass flux at different axial locations of the pipe section. The
predictions also provide the radial distribut ions of the carrier phase such as axial mean
velocity, rad ial mean velocity, root mean square of the axial gas velocity and the mean gas
temperature. The computational results are compared with the available date of Sommerfeld et al.
( 1998), and reasonable agreement was obtained.
The results indicated that the effect of the turbulence coupling between the two phases is
proportional to the mass loading ratio. This effect becomes more important with the loading ratios
encountered in many engineeri ng applications e.g. internal combustion engines and drying
processes. Different ratios of injected spray mass flow rate to that of the carrier phase are
considered to study the effect of the modified source terms on the flow properties of both the
carrier phase and the dispersed phase.