ORIGINAL_ARTICLE
Experimental and Numerical Studies on Water Cooling Tower Performance
Theoretical and experimental studies were conducted on forced draftwater cooling tower. In such towers, the heat and mass transfer take placefrom the hot water to the bulk air, which passes through the tower. Thetheoretical study includes two parts, the first part describes the numericalsolution for the water cooling tower governing equations, a two dimension airmomentum equation (Navier-Stocks equations) and air enthalpy equation(energy equation), moisture content and water enthalpy equation. The effectof turbulence was simulated using the k-ε model. The packing-air resistance isdescribed and added to the air momentum equation in y-direction only. Thesecond part highlights the use of three different packing types. This includesthe use of a ceramic packing in two different heights (0.66, 0.48m) in additionto an aluminum packing. A simple comparison between all the above types ofpacking behavior is conducted. The experimental study was conducted usingHilton water cooling tower, which is a counter flow type. The variation inmany variables, which affect the tower efficiency, are described in this part ofthe research including variation heating loads, entering water mass flow ratesand incoming air volume flow rates. The flow field velocity vector for airthrough the tower is plotted, and an accurate behavior of both air and waterproperties was found.
https://etj.uotechnology.edu.iq/article_181335_a30c3995dafa2e6a5ab22613bf18d95b.pdf
2007-04-25
512
533
10.30684/etj.25.4.1
Waheed
Mohammad
1
AUTHOR
Jalal
Jalil
2
AUTHOR
ORIGINAL_ARTICLE
Numerical Study of Flow InMechanically Ventilated Rooms Under Non- Isothermal Conditions
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 roomflow patterns in mechanically ventilated spaces. The procedure is based on thesolution in finite-volume form of 3D equation for the conservation of mass,momentum, energy, kinetic energy and dissipation rate. Effect of buoyancy onthe turbulence model has been included. The results are shown to be inreasonable agreement with experimental data
https://etj.uotechnology.edu.iq/article_181336_5367a938fe1064a223f311dbc23f263d.pdf
2007-04-25
534
542
10.30684/etj.25.4.2
Jalal
Jalil
1
AUTHOR
Talib
Murtadha
talib_km@mutah.edu.jo
2
AUTHOR
Hanaa
Ali
3
AUTHOR
ORIGINAL_ARTICLE
The Effect of Size and Location of a Heating Source on the Buoyant Flow in a Heated Space
A numerical study of two-dimensional turbulent buoyant recirculating flowswithin a heated space is presented. The study involves the solution of elliptic partialdifferential equations for the conservation of mass, momentum, energy, turbulenceenergy and its dissipation rate. These equations were solved together with algebraicexpressions for the turbulent viscosity and heat diffusivity in a finite difference form.The simulations of the turbulent buoyant flow within the space were undertakenusing two principle geometrical arrangements (A & B) of the room with differentlocations and sizes of a heating source (b/h=0.08, 0.28, and 0.5 for geometry A andb/h=0.75, 1.45, and 6.0 for geometry B). The study demonstrates that for a thermalcomfort conditions in the space the location and size of the heating source are of greatimportance. When the heating source is located in the middle of the floor it is found togenerate a high velocity air stream resulted from vortices produce a local thermaldiscomfort in the occupation zone. On the other hand its location under a coldwindow offsets the losses in heat and avoiding the form of the high velocity airstreams in the occupation zone. The size of the heating source is also found toinfluence the occupation zone condition through the effect on the heat transfer rateinside the conditioned space.
https://etj.uotechnology.edu.iq/article_181337_2660714d49eb9547ecdfce043d74b987.pdf
2007-04-25
543
557
10.30684/etj.25.4.3
Waheed
Mohammed
1
AUTHOR
Gazy
Saloomy
2
AUTHOR
Abdul-Jabar
Ahmed
3
AUTHOR
ORIGINAL_ARTICLE
Dopping Effect On Optical Constants of Polymethylmethacrylate (PMMA)
The optical constants (refractive index (n) , extinction coefficient (k) , realand imaginary parts of dielectric constant(ε1&ε2)) of polymethyl methacrylate(PMMA) doped with methylene blue (mb) and methyl red (mr) withthickness in the range (0.1-0.2) mm were measured in the wavelength range(200-900) nm. Refractive index (n) and extinction coefficient (k) showedirregular changes with increasing (mb) dopant concentrations, while (n) and(k) of PMMA doped with (mr) declared a systematic increase with increasingdopant concentrations. The data showed that (n) values of PMMA doped with(mr) are lower than the values of samples doped with (mb) which isatteributed to the progressive increase of absorbance in the wavelength range(400-550) nm with increasing (mr) concentration .
https://etj.uotechnology.edu.iq/article_181338_8d782f6229e3bf81f5bb4d22a04e42f0.pdf
2007-04-25
558
568
10.30684/etj.25.4.4
Optical Constants
Polymethylmethacrylate(PMMA)
Ahmad
H
1
AUTHOR
Awatif
M
2
AUTHOR
Zeid
N
3
AUTHOR
ORIGINAL_ARTICLE
A Finite Element Analysis of Orthogonal Machining Using Different Tool Edge Geometries
This paper summarizes the effects of edge preparation of the cutting tool inorthogonal cutting on the following variables: stress distributions at the toolrake face, cutting forces and tool-chip contact length. The Finite ElementMethod (FEM) is selected using the ANSYS /V4.5 code. Six models of cuttingtools have been suggested having edge radii of (0.01, 0.05, 0.1, 0.15, 0.2, and0.25) mm. The results obtained provide a fundamental understanding of theprocess mechanics for cutting with realistic cutting tool edge radius in order toassist in the optimization of tool edge design. The results show that theoptimum edge radius from the six simulated models is (0.05) mm; this edgeradius gives minimum value of effective stress. The results show also that theoptimum edge radius that shows minimum tangential cutting and feed forcesis (0.01) mm. The results investigated that the tool-chip contact length isincreased, until reaching maximum value of (2.4) mm at (r=0.15mm), andminimum value of (0.75) mm at (r=0.01mm). The maximum relativedifference between simulated results of this work and other previous paperresults is (2% - 17%) for the tool effective stresses, (5%) for the tangentialforce, and (11%) for the feed force.
https://etj.uotechnology.edu.iq/article_181339_453bf8064bb2df16ad01223c7252b3d0.pdf
2007-04-25
569
583
10.30684/etj.25.4.5
FEM
edge radius
orthogonal machining
Maan
Tawfiq
70057@uotechnology.edu.iq.
1
AUTHOR
Suha
Shahab
2
AUTHOR
ORIGINAL_ARTICLE
Normalized Characteristics of Laser-Induced Diffusion of Arsenic Dopants in Silicon
In this work, normalized characteristics of laser-induced diffusion ofarsenic in silicon are presented. These characteristics are considered as areenhancing the As-doped silicon-based devices. This enhancement is attributedto the increasing in the diffusion length within a certain layer of the activeregion in the device. Laser-induced diffusion is a perfect technique forimproving the characteristics of electronic devices because it is flexible,contactless, clean and well controlled.
https://etj.uotechnology.edu.iq/article_181340_8ee05de2f8dd5fd277770343f2eb21e0.pdf
2007-04-25
584
590
10.30684/etj.25.4.6
Laser-induced diffusion
Arsenic-doped silicon
Transistor current gain
Oday
Hamadi
1
AUTHOR
Salma
Hussain
2
AUTHOR
ORIGINAL_ARTICLE
The Effect of Surfactants on Characteristics of Hydrodynamic and Mass Transfer Coefficient in Gas-Liquid Dispersion Column
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) andsuperficial air velocity (1-15cm/s) on the gas holdup and mass transfercoefficient in air-liquid dispersion column. The experimental procedure wascarried out by QVF column (10 cm i.d, 1.5 m height) and air bubbling bymulti-orifice distributor (2 mm, 49 holes in square pitch). The experimentalresults are presented in two and three dimension graphs, these graphsindicate, increases in holdup and mass transfer coefficient with increasingweight percent of alcohols, temperature, and superficial velocity of air. Thegas holdup and mass transfer coefficient are in the following ordern-butanol > i-propanol > water. Also the experimental results were correlatedby fitting empirical correlations.Some of the results have been correlated on the basis of drift flux modelin order to express the effect of surface active agent on radial uniformity flowand gas holdup profiles
https://etj.uotechnology.edu.iq/article_181341_c68ee8e24fb9c674c26f455274b02cc4.pdf
2007-04-25
591
607
10.30684/etj.25.4.7
Gas-liquid dispersion column
surface active agent
Gas holdup
Mass transfer coefficient
Thamer
Mohammed
thamer_jasim58@yahoo.com
1
AUTHOR
Fadi
Hanna
2
AUTHOR
ORIGINAL_ARTICLE
Modelling Pressure Drop to Calculate Conversion of Silicon and Methyl Chloride in a Fluidized bed Reactor
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, inorder 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 fluidizationvelocity [velocity selected 2.6 cm/s, minimum fluidization velocity 1.8 cm/s] for the solidparticles (size used 130 μm). A digital pressure drop measuring device was used at threepoints of the reactor (before and after the distributor and finally 50 cm above thedistributor), to determine the pressure drop along the column, also an online GC wasconnected to the outlet reacted gas to analyze the product.A comparison between the conversions of methyl chloride and silicon calculatedfrom pressure drop data and that detected by the online GC, show a proper agreementwith less than 5 %absolute average error.Two equations [16, 18], derived analytically, were equation [8, 18] used tocalculate 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 ofmethyl chloride.
https://etj.uotechnology.edu.iq/article_181342_b032ad64963920f38e417bbaf1f9deec.pdf
2007-04-25
608
618
10.30684/etj.25.4.8
fluidized bed reactor
Pressure drop
reactor modelling
Ihsan
Hamawand
1
AUTHOR
ORIGINAL_ARTICLE
A Numerical Model For Thermal-Hydraulic Design of a Shell And Single Pass Low Finned Tube Bundle Heat Exchanger
This investigation represents a computerized model for the thermal-hydraulicdesign of a single shell – single pass of enhance tube bundle heat exchanger usingthe step by step technique (SST). The design procedure suggested in this study isalso suitable for multi-tube passes using the most familiar methods of design ofshell and tube heat exchanger such as Kern and Bell-Delaware. The (SST) wasconsidered as a basic in order to incorporate the effect of the physical propertychange due to temperature variation along the heat exchanger. The model basicdesign depends on the selection of the low finned tube characteristics. The use ofsuch surface will have the advantage of avoiding the space restrictions of theequipment layout in the industrial applications and reduction in the cost ofmanufacture machining as well. The model was intended to be a choice for thelubricating oil cooling system of a gas turbine power station in Debis-Kirkukplant. The verification of the model showed that using such enhanced tubes in thecooling system will improve the operating conditions especially during summerseason in Iraq.
https://etj.uotechnology.edu.iq/article_181343_6686b3d8695ca27bedfe3bc1c9512fd8.pdf
2007-04-25
619
645
10.30684/etj.25.4.9
Heat Exchangers Design
Single Phase
Shell and Tube
Enhanced Surfaces
Low Finned Tube
Ali
Tarrad
1
AUTHOR
ORIGINAL_ARTICLE
Secure E-Mail System Using S/Mime and Ib-Pkc
Although e-mail security solutions have been introduced formore than two decades, most of the e-mail messages are sent nowadayswithout being secured by any of these techniques. This is due to thecomplexity of using these secure e-mail systems and protocols. Thecomplexity mainly arises from the difficulty associated with managingcertificates and public keys. The main objective of this study was to finda solution that can make secure e-mail systems easier to use whilemaintaining the same level of security. This paper proposes a secure emailsystem that is based on the S/MIME standard where the publickey and signature algorithms have been replaced by their Identity-Based Cryptography analogue algorithms.Using Identity-Based Cryptography has eliminated the need fordigital certificates, and provided a solution to the usability problempresent in the existing secure e-mail systems. Users can determine thepublic key of the recipient without having to contact any trusted thirdparty, and can start encrypting or verifying messages as long as theyhave the public system parameters that can be publicly available. Usersneed to contact the Private Key Generator (PKG) only once in order toretrieve their private key before being able to decrypt or sign messages
https://etj.uotechnology.edu.iq/article_181344_6ea9aef8f59e61b1bf184061436acde3.pdf
2007-04-25
646
668
10.30684/etj.25.4.10
Secure E-mail
S/MIME
Identity-Based Cryptography
IBE
IBS
security
Usability
Sufyan
Faraj
1
AUTHOR
Mohammed
Ibrahem
2
AUTHOR