Print ISSN: 1681-6900

Online ISSN: 2412-0758

Volume 25, Issue 4

Volume 25, Issue 4, June 2007, Page 512-668

Experimental and Numerical Studies on Water Cooling Tower Performance

Waheed Sh.Mohammad; Jalal M. Jalil; Essam O. Ali

Engineering and Technology Journal, 2007, Volume 25, Issue 4, Pages 512-533

Theoretical and experimental studies were conducted on forced draft
water cooling tower. In such towers, the heat and mass transfer take place
from the hot water to the bulk air, which passes through the tower. The
theoretical study includes two parts, the first part describes the numerical
solution for the water cooling tower governing equations, a two dimension air
momentum equation (Navier-Stocks equations) and air enthalpy equation
(energy equation), moisture content and water enthalpy equation. The effect
of turbulence was simulated using the k-ε model. The packing-air resistance is
described and added to the air momentum equation in y-direction only. The
second part highlights the use of three different packing types. This includes
the use of a ceramic packing in two different heights (0.66, 0.48m) in addition
to an aluminum packing. A simple comparison between all the above types of
packing behavior is conducted. The experimental study was conducted using
Hilton water cooling tower, which is a counter flow type. The variation in
many variables, which affect the tower efficiency, are described in this part of
the research including variation heating loads, entering water mass flow rates
and incoming air volume flow rates. The flow field velocity vector for air
through the tower is plotted, and an accurate behavior of both air and water
properties was found.

Numerical Study of Flow In Mechanically Ventilated Rooms Under Non- Isothermal Conditions

Hanaa M. Mohammed Ali; Talib K. Murtadha; Jalal M. Jalil

Engineering and Technology Journal, 2007, Volume 25, Issue 4, Pages 534-542

A computational procedure was conducted in (3x3x3 m) rooms and in a full–
scale model building to study the effect of supply temperature on the room
flow patterns in mechanically ventilated spaces. The procedure is based on the
solution in finite-volume form of 3D equation for the conservation of mass,
momentum, energy, kinetic energy and dissipation rate. Effect of buoyancy on
the turbulence model has been included. The results are shown to be in
reasonable agreement with experimental data.

The Effect of Size and Location of a Heating Source on the Buoyant Flow in a Heated Space

Waheed S. Mohammed; Gazy F. Saloomy; Abdul-Jabar Muttair Ahmed

Engineering and Technology Journal, 2007, Volume 25, Issue 4, Pages 543-557

A numerical study of two-dimensional turbulent buoyant recirculating flows
within a heated space is presented. The study involves the solution of elliptic partial
differential equations for the conservation of mass, momentum, energy, turbulence
energy and its dissipation rate. These equations were solved together with algebraic
expressions for the turbulent viscosity and heat diffusivity in a finite difference form.
The simulations of the turbulent buoyant flow within the space were undertaken
using two principle geometrical arrangements (A & B) of the room with different
locations and sizes of a heating source (b/h=0.08, 0.28, and 0.5 for geometry A and
b/h=0.75, 1.45, and 6.0 for geometry B). The study demonstrates that for a thermal
comfort conditions in the space the location and size of the heating source are of great
importance. When the heating source is located in the middle of the floor it is found to
generate a high velocity air stream resulted from vortices produce a local thermal
discomfort in the occupation zone. On the other hand its location under a cold
window offsets the losses in heat and avoiding the form of the high velocity air
streams in the occupation zone. The size of the heating source is also found to
influence the occupation zone condition through the effect on the heat transfer rate
inside the conditioned space.

Dopping Effect On Optical Constants of Polymethylmethacrylate (PMMA)

Ahmad A.H; Awatif A.M; Zeid Abdul-Majied N

Engineering and Technology Journal, 2007, Volume 25, Issue 4, Pages 558-568

The optical constants (refractive index (n) , extinction coefficient (k) , real
and imaginary parts of dielectric constant(ε1&ε2)) of polymethyl methacrylate
(PMMA) doped with methylene blue (mb) and methyl red (mr) with
thickness in the range (0.1-0.2) mm were measured in the wavelength range
(200-900) nm. Refractive index (n) and extinction coefficient (k) showed
irregular changes with increasing (mb) dopant concentrations, while (n) and
(k) of PMMA doped with (mr) declared a systematic increase with increasing
dopant concentrations. The data showed that (n) values of PMMA doped with
(mr) are lower than the values of samples doped with (mb) which is
atteributed to the progressive increase of absorbance in the wavelength range
(400-550) nm with increasing (mr) concentration

A Finite Element Analysis of Orthogonal Machining Using Different Tool Edge Geometries

Suha Kareem Shahab; Maan Aabid Tawfiq

Engineering and Technology Journal, 2007, Volume 25, Issue 4, Pages 569-583

This paper summarizes the effects of edge preparation of the cutting tool in
orthogonal cutting on the following variables: stress distributions at the tool
rake face, cutting forces and tool-chip contact length. The Finite Element
Method (FEM) is selected using the ANSYS /V4.5 code. Six models of cutting
tools have been suggested having edge radii of (0.01, 0.05, 0.1, 0.15, 0.2, and
0.25) mm. The results obtained provide a fundamental understanding of the
process mechanics for cutting with realistic cutting tool edge radius in order to
assist in the optimization of tool edge design. The results show that the
optimum edge radius from the six simulated models is (0.05) mm; this edge
radius gives minimum value of effective stress. The results show also that the
optimum edge radius that shows minimum tangential cutting and feed forces
is (0.01) mm. The results investigated that the tool-chip contact length is
increased, until reaching maximum value of (2.4) mm at (r=0.15mm), and
minimum value of (0.75) mm at (r=0.01mm). The maximum relative
difference between simulated results of this work and other previous paper
results is (2% - 17%) for the tool effective stresses, (5%) for the tangential
force, and (11%) for the feed force.

Normalized Characteristics of Laser-Induced Diffusion of Arsenic Dopants in Silicon

Aseel A.K. Hadi; Salma M. Hussain; Oday A. Hamadi; Rana O. Mahdi

Engineering and Technology Journal, 2007, Volume 25, Issue 4, Pages 584-590

In this work, normalized characteristics of laser-induced diffusion of
arsenic in silicon are presented. These characteristics are considered as are
enhancing the As-doped silicon-based devices. This enhancement is attributed
to the increasing in the diffusion length within a certain layer of the active
region in the device. Laser-induced diffusion is a perfect technique for
improving the characteristics of electronic devices because it is flexible,
contactless, clean and well controlled

The Effect of Surfactants on Characteristics of Hydrodynamic and Mass Transfer Coefficient in Gas-Liquid Dispersion Column

Ihsan B. Hamawand; Fadi Z. Hanna; Thamer J. Mohammed

Engineering and Technology Journal, 2007, Volume 25, Issue 4, Pages 591-607

This work studis the effect of liquid properties (water, solution 0.2-1.5 wt
% for each of i-propanol, and n-butanol), temperature (26-55 oC) and
superficial air velocity (1-15cm/s) on the gas holdup and mass transfer
coefficient in air-liquid dispersion column. The experimental procedure was
carried out by QVF column (10 cm i.d, 1.5 m height) and air bubbling by
multi-orifice distributor (2 mm, 49 holes in square pitch). The experimental
results are presented in two and three dimension graphs, these graphs
indicate, increases in holdup and mass transfer coefficient with increasing
weight percent of alcohols, temperature, and superficial velocity of air. The
gas holdup and mass transfer coefficient are in the following order
n-butanol > i-propanol > water. Also the experimental results were correlated
by fitting empirical correlations.
Some of the results have been correlated on the basis of drift flux model
in order to express the effect of surface active agent on radial uniformity flow
and gas holdup profiles.

Modelling Pressure Drop to Calculate Conversion of Silicon and Methyl Chloride in a Fluidized bed Reactor

Ihsan B. Hamawand

Engineering and Technology Journal, 2007, Volume 25, Issue 4, Pages 608-618

Three experiments were curried out at different reaction temperatures [ 250, 300,
330 oC ], for the reaction of silicon with methyl chloride in a fluidized bed reactor, in
order to evaluate a new predicted model that calculate both conversions of reacted solid
(silicon) and reacted gas (methyl chloride) as function of pressure drop along the bed.
The reacted gas velocity was selected to be above the minimum fluidization
velocity [velocity selected 2.6 cm/s, minimum fluidization velocity 1.8 cm/s] for the solid
particles (size used 130 μm). A digital pressure drop measuring device was used at three
points of the reactor (before and after the distributor and finally 50 cm above the
distributor), to determine the pressure drop along the column, also an online GC was
connected to the outlet reacted gas to analyze the product.
A comparison between the conversions of methyl chloride and silicon calculated
from pressure drop data and that detected by the online GC, show a proper agreement
with less than 5 % absolute average error.
Two equations [16, 18], derived analytically, were equation [8, 18] used to
calculate the conversion of silicon and methyl chloride as function of pressure drop,
equation [16] used to calculate the conversion of silicon as function of conversion of
methyl chloride.

A Numerical Model For Thermal-Hydraulic Design of a Shell And Single Pass Low Finned Tube Bundle Heat Exchanger

Ali Hussain Tarrad

Engineering and Technology Journal, 2007, Volume 25, Issue 4, Pages 619-645

This investigation represents a computerized model for the thermal-hydraulic
design of a single shell – single pass of enhance tube bundle heat exchanger using
the step by step technique (SST). The design procedure suggested in this study is
also suitable for multi-tube passes using the most familiar methods of design of
shell and tube heat exchanger such as Kern and Bell-Delaware. The (SST) was
considered as a basic in order to incorporate the effect of the physical property
change due to temperature variation along the heat exchanger. The model basic
design depends on the selection of the low finned tube characteristics. The use of
such surface will have the advantage of avoiding the space restrictions of the
equipment layout in the industrial applications and reduction in the cost of
manufacture machining as well. The model was intended to be a choice for the
lubricating oil cooling system of a gas turbine power station in Debis-Kirkuk
plant. The verification of the model showed that using such enhanced tubes in the
cooling system will improve the operating conditions especially during summer
season in Iraq.

Secure E-Mail System Using S/Mime and Ib-Pkc

Sufyan T. Faraj; Mohammed T. Ibrahem

Engineering and Technology Journal, 2007, Volume 25, Issue 4, Pages 646-668

Although e-mail security solutions have been introduced for
more than two decades, most of the e-mail messages are sent nowadays
without being secured by any of these techniques. This is due to the
complexity of using these secure e-mail systems and protocols. The
complexity mainly arises from the difficulty associated with managing
certificates and public keys. The main objective of this study was to find
a solution that can make secure e-mail systems easier to use while
maintaining the same level of security. This paper proposes a secure email
system that is based on the S/MIME standard where the public
key and signature algorithms have been replaced by their Identity-
Based Cryptography analogue algorithms.
Using Identity-Based Cryptography has eliminated the need for
digital certificates, and provided a solution to the usability problem
present in the existing secure e-mail systems. Users can determine the
public key of the recipient without having to contact any trusted third
party, and can start encrypting or verifying messages as long as they
have the public system parameters that can be publicly available. Users
need to contact the Private Key Generator (PKG) only once in order to
retrieve their private key before being able to decrypt or sign messages.