2009
43
1
1
0
1

ارزیابی عملکرد نوارهای پیچیده شده درافزایش انتقال حرارت چگالشی و تأثیر آن برمیزان افت فشار
https://jac.ut.ac.ir/article_7669.html
1
In this research, heat transfer enhancement and simultaneous effect of that on pressure drop inside condensers with twisted tape inserts are investigated. A refrigeration system is designed for attaining to maximum level of heat transfer with minimum pressure drop. The test condenser is a double pipe heat transformer with inner and outer diameter of 10.7mm and 12.7mm for internal pipe, respectively. The test tube’s length is 104mm. Experiments are performed for a plain tube and four tubes with twisted tape inserts with different twist ratios of 6, 9, 12 and 15. Also data are collected for mass velocities of 56.44, 69.49, 82.38, 96.52, 113.32 and 130.9kg/m2s. In conclusion, data analysis showed that insertion of twisted tapes inside tubes has increased the heat transfer and pressure drop by as much as 40% and 240% above the plain tube values on a nominal area basis, respectively.
0

1
9


Mohammad Ali
Akhavan
Iran


Vahid
Hejazi
Iran
Pressure Drop
Twisted Tape
R134a
Twist Ratio
Condensation
Heat Transfer
1

تحلیل و بهینهسازی سازههای ساندویچی با هسته سینوسی
https://jac.ut.ac.ir/article_7670.html
1
In this paper a special sandwich panel with a sinusoidal core under distributed load on upper and lower plates has been studied. By drawing free body diagrams, and using energy method and Castagiliano theory the forces and moments involved in the core has been determined. Then, the stresses, normal and horizontal displacements due to above forces and moments are calculated. In order to ensure the accuracy of the analysis, the results obtained are verified by using ANSYS software. Finally, by use of displacement as a constraint for sandwich panel, optimization is carried out for this problem by genetic algorithm and MOEA toolbox in MATLAB environment. The results obtained from optimization and other analysis show a very good agreement.
0

11
20


Mohammad Kazem
Besharati Givi
Iran


Mehdi
Ghasemi
Iran


Seyyed Mahmoud
Mousavi Mashhadi
Iran
MATLAB
ANSYS
genetic algorithm
MOEA
Sandwich Materials
1

تحلیل کرانه فوقانی اکستروژن مستقیم چرخ دنده های ساده باپروفیل دندانه اصلاح شده
https://jac.ut.ac.ir/article_7671.html
1
This paper describes an upper bound analysis of cold forward extrusion of spur gears with modified tooth profile. Spur gear geometrical parameters such as module, number of teeth, pressure angle, bore radius and addendum modification factor were input to a computer program written in Visual Basic. Then spur gear, billet and extrusion die cavity were modeled automatically in SolidWorks. For upper bound analyses, half pitch of a tooth was considered as a deformation unit and it has been divided into twelve regions and it is assumed that material flow in each region is axisymmetric. Comparison between present theoretical results and the experimental data of other researchers’ work were carried out to illustrate the validity of this proposed model. Finally effects of various parameters on the extrusion load were studied.
0

21
29


Ehsan
Khademi
Iran


Heshmatollah
Haghighat
Iran
Forward Extrusion
Upper bound
Geometric Modeling
Spur Gear
1

بررسی ناپایداری جریان های دوبعدی موازی در سیالات ویسکوالاستیک با استفاده از روش های شبه طیفی
https://jac.ut.ac.ir/article_7672.html
1
In the present work, the effect of fluid’s elasticity was investigated on the hydrodynamic instability of Blasius flow. To determine the critical Reynolds number as a function of the elasticity number, a twodimensional linear temporal stability analysis was invoked. The viscoelastic fluid is assumed to obey the Walters’ B fluid model for which base flow velocity profiles were fortunately available from literature. Neglecting terms nonlinear in the perturbation quantities, a Generalized OrrSommerfeld equation was obtained incorporating an elastic term. The eigenvalue problem so obtained was solved numerically using the Chebychev collocationpoint method. Based on the results obtained in this work, fluid’s elasticity is predicted to have a destabilizing effect on the Blasius flow.
0

31
37


Navid
Khabbazi
Iran


Keyvan
Sadeghi
Iran
Hydrodynamic Instability
Elasticity Number
Critical Reynolds Number
Blasius Flow
Second Order Fluid
Non Newtonian Fluids
1

کاربرد مدل های k? خطی و غیر خطی در پیش بینی جریان و انتقال حرارت جا به جائی در کانال های با موانع منفصل
https://jac.ut.ac.ir/article_7673.html
1
Roughness elements or turbulence promoters have been widely used to enhance heat transfer in cooling passages of modern gas turbine blades. Although such ribs substantially enhance heat transfer, the heat transfer coefficient is reduced immediately at corner downstream of each rib, creating hot spots. To remove such hot spots some of the ribs can be detached from the channel walls. In this paper, this idea is investigated using numerical methods. In this study, turbulent flow and heat transfer through three types of channels, namely: 1) a channel with detached ribs from a wall 2) a channel with detached ribs from both walls and 3) a channel with alternative attacheddetached ribs on both walls have been investigated. Computations presented in this research have been obtained with the linear and nonlinear k? models. The numerical method in this work is finite volume methodology and simple algorithm. The governing equations are discretized in a semistaggered grid system. In all equations the convective terms are approximated using Hybrid scheme. The numerical results for the channel with detached ribs close to one principal wall showed that both the linear and nonlinear k? models are able to predict the length and width of the wake downstream of the detached ribs, although both models produce weaker wakes compared with experimental data. Both models "specially the nonlinear k? model" predict lower streamwise velocity and turbulent intensities closed to the ribbed wall. As a result, both turbulence models "and specially the nonlinear k? model" substantially underpredict the wall heat transfer. For the channel with ribs detached close to both walls, both turbulence models produce better heat transfer predictions though still predict lower heat transfer levels. Finally, for the channel with alternative attacheddetached ribs, both turbulence models fail to predict reliable heat transfer levels in first half of the channel but return acceptable Nusselt levels in the second half of the channel.
0

39
49


Mehrdad
Raisee Dehkordi
Iran


Arman
Rokhzadi
Iran
Turbulent Heat Transfer
Gas Turbine
Cooling
1

کمانش پوستههای استوانهای با گشودگی شبه بیضوی تحت فشار محوری
https://jac.ut.ac.ir/article_7674.html
1
Understanding how a cutout influences the load bearing capacity and buckling behavior of cylindrical shells is fundamental in the design of structural components used in automobiles, aircrafts, and marine structures. In this article, simulation and analysis of steel cylindrical shells with various lengths, include quasi elliptical cutout, subjected to axial compression were systematically carried out using finite element numerical method and the investigation examined the influence of the cutout size, cutout angle and the shell aspect ratio (L/D) on the buckling, and postbuckling responses of the moderately thick steel cylindrical shells. For several specimens an experimental investigation was also carried out via an INSTRON 8802 servo hydraulic machine. And the results obtained from the experiments were compared with numerical results. A very good accordance was observed between the results obtained from the finite element simulation and the experiments. Finally, corresponding to experimental and numerical results, an equation was presented for finding buckling load of such structures.
0

51
63


Mahmoud
Shariati
Iran


Masoud
Mehdizadeh Rokhi
Iran
Finite Element Method
Semi Elliptical Cutout
Buckling
Cylindrical Shells
Experimental Method
1

بررسی شکل دهی معکوس شوندة صفحات نازک با در نظر گرفتن پدیدة باشینگر
https://jac.ut.ac.ir/article_7675.html
1
This paper investigates the forming of sheet metal forming under cycling loading by considering the Bauschinger effect. Different proposed plasticity models which can handle this kind of deformation process have been reviewed in details. For instance, isotropic, kinematic and combined forms in the linear and nonlinear cases including the wellknown Yoshida and Chaboche's models have been studied. The ability of the best proposed model has been examined in the forming of reverse cup drawing and the obtained results have been compared with some other experimental results. The normalized axial stress, vonmises stress and the punch forces for both first and second stages have been calculated for different materials and thicknesses.
0

65
77


Mehran
Kadkhodayan
Iran


Javad
Mosayyebi
Iran
Sheet Metal
Bauschinger Effect
Reverse Cup Drawing
1

تحریک لایه مرزی آشفته توسط جت و وِیک و اثر آن بر ضریب انتقال حرارت از صفحه تخت
https://jac.ut.ac.ir/article_7676.html
1
0

79
88


Mohsen
Kahrom
Iran


Behrouz
Zafarmand
Iran


Ali
Farahbod
Iran
Boundary Layer Disturbed
Jet and Wake Effect
Heat Transfer Enhancement
Numerical Method
1

تأثیر مدلسازی تراک1 در محاسبه خواص موج بلاست ناشی از انفجار ابر هوا سوخت
https://jac.ut.ac.ir/article_7677.html
1
In this work the effect of the accuracy of a FAE detonation modeling on the generated blast wave is investigated. First, a onedimensional numerical simulation with a reduced chemical kinetics of C2H2O2Ar, involving 25 elementary reactions, is used as the base model. The properties of the blast calculated with this model is compared with those of simpler models, the similarity solution of Taylor, the constant volume (CV) explosion model, and the CJburn model. It is found that the result of Taylor's similarity model is in very good agreement with the result of the base model. The blast properties that calculated with the CJburn model are also in close agreement with those of the base and Taylor's models. However, the CV model prediction shows considerable difference with the base model. Considering the computational cost and the accuracy, the Taylor's model is recommended as the favorite model for the calculation of the FAE blast properties.
0

89
102


Kiumars
Mazaheri
Iran


Ali
Tarokh
Iran
Chemical Kinetics
PPM
Blast Wave
FAE
Numerical simulation
Detonation Wave
1

بهینه سازی تک معیاره و چند معیاره برج خنک کن خشک هلر در نیروگاههای سیکل ترکیبی با استفاده از الگوریتم ژنتیک
https://jac.ut.ac.ir/article_7678.html
1
In this paper the effect of site conditions, which are Altitude, Temperature and Relative Humidity and also Heat Dissipation Capacity are investigated on the optimized design of natural draft dry cooling towers with specific kind of heat exchangers, known as Forgo T60 type. A genetic algorithm program has been developed for optimized design of these cooling towers. Objective function includes both cost and performance of the tower. The optimized dimensions of the tower, the number of heat exchangers and mass flow rate of water and air are the results of this optimization program. The results show it is possible to find the variation of the optimized value of each design variable versus the variations of the site conditions and heat dissipation capacity. Also finding an optimum for all design parameters for any site condition is possible; however it is very dependent on how exact the cost analysis is.
0

111
124


Hassan
Shokouhmand
Iran


Mohammad Ali
Nazari
Iran


Babak
Ghaem Panah
Iran


Mohammad Reza
Aligoodarzi
Iran
Dry Cooling
genetic algorithm
Temperature Variation
Characteristic Curve
Performance
Natural Draft
Forgo type Heat Exchanger
Optimization
1

پیش بینی زبری سطح در تراش کاری خشک به کمک شبکه های فازی عصبی تطبیقی
https://jac.ut.ac.ir/article_7679.html
1
Optimization of machining parameters is very important and the main goal in every machining process. Surface finishing prediction is a prerequirement to establish a center for automatic machining operations. In this research, a neurofuzzy approach is used in order to model and predict the surface roughness in dry turning. This approach has both the learning capability of neural network and linguistic representation of complex and indefinite phenomena in lingual phrases forms. A model which represents the influence of machining parameters and tool properties on surface roughness is established first. Then, this model is edited via the usage of results of training data. Finally, the efficiency of neurofuzzy model is evaluated via the comparison between the model's output and the output of surface roughness obtained from the theoretical formula.
0

103
110


Ramezan Ali
Mahdavi Nejad
Iran


Kamran
Tamimi
Iran
Fuzzy Rules
Adaptive Neural Fuzzy Intelligent System
Surface Roughness
Membership Function
1

پیشبینی جریان و انتقال حرارت در کانالهای ریبدار سه بعدی توسط مدلهای ?K خطی و غیرخطی
https://jac.ut.ac.ir/article_7680.html
1
The present paper deals with the prediction of threedimensional fluid flow and heat transfer in ribroughened ducts of square crosssection. Such flows are of direct relevance to the internal cooling system of modern gas turbine blades. The main objective is to assess how a recently developed variant of a cubic nonlinear model (proposed by Craft et al. (1999)), that has been shown to produce reliable thermal predictions through axisymmetric and plane twodimensional ribbed passages (Raisee et al. (2004)), can predict flow and heat transfer characteristics through more complex threedimensional ribbed ducts. To fulfil this objective, the present paper discusses turbulent air flow and heat transfer through two different configurations, namely: (I) a square duct with “inline” ribs normal to the flow direction at and (II) a square duct with normal ribs in a “staggered” arrangement at . In this paper the flow and thermal predictions of the linear model (EVM) are also included, as a set of baseline predictions. Both turbulence models have been used with the form of lengthscale correction term to the dissipation rate originally proposed by ‘Yap’ and also a differential version of this term, ‘NYP’. The mean flow predictions show that both linear and nonlinear models can successfully reproduce most of the measured data for streamwise and crossstream velocity components. Moreover, the nonlinear model, which is sensitive to turbulence anisotropy, is able to produce better results for the turbulent stresses. As far as heat transfer predictions are concerned, it was found that both EVM and NLEVM2, the more recent variant of the nonlinear , with the algebraic lengthscale correction term, overestimate the measured Nusselt numbers for both geometries examined. While the EVM with the differential lengthscale correction term underestimates heat transfer levels, the Nusselt number predictions with the NLEVM2 and the ‘NYP’ term are in close agreements with the measured data. Comparisons with our earlier work, Iacovides and Raisee (1999), show that the NLEVM2 thermal predictions are of similar quality to those of a secondmoment closure. This modified version of the nonlinear model, that in earlier studies was shown to improve thermal predictions in axisymmetric and plane ribbed passages, is thus now found to also produce reasonable heat transfer predictions in threedimensional ribbed ducts.
0

125
138


Hooman
Naimi
Iran


Mehrdad
Raisee
Iran
Heat Transfer
Turbulence
Modeling
Gas Turbine