2020-09-30T05:58:21Z
https://ajme.aut.ac.ir/?_action=export&rf=summon&issue=113
AUT Journal of Mechanical Engineering
AJME
2588-2945
2588-2945
2017
1
1
Investigation of Mixed Electro-Osmotic/Poiseuille Slip Flows of Viscoelastic Fluids in Rectangular Microchannels with Hydrophobic Surfaces
M.
Reshadi
M. H.
Saidi
In this paper, we conduct a numerical study of mixed electro-osmotic/Poiseuille slip flows ofviscoelastic fluids in microchannels with rectangular cross sections by means of second order finite differencemethod. In this regard, the complete form of the PTT-constitutive equation is used to describe the rheologicalbehavior of the fluid. The numerical results being validated by the same simplified theoretical study reveal anexcellent accuracy with relative error less than 0.3%. Afterward, the extended numerical study is used to investigate the 2D velocity distribution and volumetric flow rate in the presence of wall surface hydrophobicity through rectangular microchannels. In addition, in this investigation, the exact solution of unidirectional electroosmotic flow of PTT-viscoelastic fluids is derived for slit hydrophobic microchannels, and after validating, the solution is used to investigate the rheological behavior of viscoelastic fluids in the range of operating parameters. The results exhibit a uniform effect of hydrophobicity in increasing the profile of 1D velocity distribution in slit microchannels. Finally, in order to determine the stability of the grid network, various under relaxation factors are applied to determine the speed of convergence of finite difference method, and then, by using the analytical procedure, the critical Weissenberg number is introduced as a function of velocity scale ratio and Debye–Hückel parameter. The evaluation of the numerical method in the critical area indicates the stability of viscoelastic fluid flow for the values of the Weissenberg number less than the corresponding critical value in the theoretical analysis.
Electro-osmosis
Viscoelasticity
Hydrophobicity
Microfluidics
2017
06
01
3
12
https://ajme.aut.ac.ir/article_715_9d4fe4f0850d2e5540a94fc246a76806.pdf
AUT Journal of Mechanical Engineering
AJME
2588-2945
2588-2945
2017
1
1
Numerical Investigation of Nano Particles Dispersion and Deposition in Fully Developed Laminar Pipe Flows
P.
Talebizadeh
H.
Rahimzadeh
G.
Ahmadi
R.
Brown
K.
Inthavong
The aim of this paper is to study the deposition and dispersion of nano particles in fully developed laminar pipe flows numerically. To simulate particle transport and to locate the position of particles, the Eulerian - Lagrangian method is used under the conditions of one-way coupling. Due to studied range of particle diameters from 5 nm to 100 nm, the main effective force for particle deposition is the Brownian diffusion force. After studying the mesh independency and validating results, time history analysis of particle transport is also performed by injecting the particles from the inlet surface and tracking them at each moment. Furthermore, the effective parameters, i.e. particle diameter, pipe length and diameter, temperature and particle density are studied comprehensively. The results of time history analysis of particle transport show that nano particles with less diameters are more deposited in less time. Furthermore, maximum number of escaped particles from the pipe occurred at 0.035 s after injecting the particles for all studied particle diameters due to the studied flow rate and length of the pipe. The output of this study can provide a guideline for evaluating nano particle transport and deposition in fully developed laminar pipe flows.
Two phase gas – solid flow
nano particles
Particle deposition
Fully developed laminar flow
Lagrangian particle tracking
2017
06
01
13
20
https://ajme.aut.ac.ir/article_762_fc5307a659c4fee0e725733fb3738685.pdf
AUT Journal of Mechanical Engineering
AJME
2588-2945
2588-2945
2017
1
1
Experimental Study of Subcooled Pool Boiling around a Circular Rough Cylinder
M.
Yaghoubi
K.
Hirbodi
M. R.
Nematollahi
S.
Bashiri
Subcooling degree and surface roughness are two major parameters that have a considerable effect on boiling heat transfer. In the present study, the effects of subcooling degree on pool boiling heat transfer coefficient and surface temperature distribution are investigated experimentally. Tests are conducted for saturated and subcooled water with different subcooling degrees in the local atmospheric pressure (863 mbar) around a horizontal stainless steel cylinder with specific surface roughness. The test section is a pool with dimensions of 120×400×550 mm and test case is a circular cylinder with 80 mm length, 9 mm diameter and 0.794 μm average surface roughness. In this research, experiments are performed for the degrees of subcooling between 5.5°C to 45.5°C and for the heat fluxes between 0.31 kW/m32 to 125.62 kW/m. Results show that by increasing the degree of subcooling for a specific average surface roughness, average surface temperature is decreased and due to changes in the mechanism of heat transfer from nucleate boiling to natural convection, heat transfer coefficient is also decreased. In the region of natural convection, the variation of heat transfer coefficient with heat flux is low and when boiling process begins, this variation is more considerable. Furthermore, for lower heat fluxes (less than 5 kW/m), the temperature difference between upper and lower sides of the test case is less than 1°C which increases for higher heat fluxes so that for more than 100 kW/m2,it reaches to 6°C.
Subcooling degree
Pool boiling
Natural convection
heat transfer coefficient
circular rough cylinder
2017
06
01
21
28
https://ajme.aut.ac.ir/article_793_b41303b04aae67b25d0160c0a4842d58.pdf
AUT Journal of Mechanical Engineering
AJME
2588-2945
2588-2945
2017
1
1
Numerical Analysis of In-Cylinder Flow in Internal Combustion Engines by LES Method
M.
Khorramdel
H.
Khaleghi
Gh.
Heidarinejad
M. H.
Saberi
In this research, Large Eddy Simulation of in-cylinder flow during suction and compression stroke in an axisymmetric engine is performed. A computer code using Smogorinsky subgrid model is developed to solve the governing equations of the flow. A proper understanding of flow during suction and compression strokes, gives better information for fuel/air mixture and combustion. The results show that the advantage of LES model is the ability of computing turbulence characteristics in various crank angles of engine cycle. This advantage of model is highlighted by calculating RMS values of axial velocity in comparison with experimental ones. The results show that axial velocity fluctuations during intake reaches to a higher level than in compression stroke because of the inlet jet to the cylinder and intensive gradient of variables. In this regard, the flow in 100 degree ATDC during intake stroke reaches the maximum level of turbulence intensity and then turbulence generated during intake stroke decays rapidly. During intake stroke, three main vorticities are generated inside the cylinder. In the compression stroke these three vorticities are merged together to establish a new vorticity with direction of rotation opposite to the intake flow. Some smaller recirculating regions are also generated at 90 degree BTDC.
Internal Combustion Engines
In-Cylinder Flow
Large Eddy Simulation
Crank Angle
2017
06
01
29
38
https://ajme.aut.ac.ir/article_748_d956d0fde80ac89378f16efa08fdb758.pdf
AUT Journal of Mechanical Engineering
AJME
2588-2945
2588-2945
2017
1
1
Comparative Analysis on Thermal Performance of Different Natural-draft Dry Cooling Towers under Crosswind Condition
M.
Goodarzi
P.
Mohammadi
This article aims to study the thermal performances of four different natural draft coolingtowers under crosswind condition. The windbreakers and the oblique exit plane have been simultaneouslyincluded in the structure of the new cooling tower. A finite volume method using SIMPLE algorithm wasused to simulate the flow field around each cooling tower. The thermal performance of the new geometryhas been compared with those of others for the generally investigated wind velocity profile for 10 m/s,and also two uniform wind velocities for 3 and 7 m/s. The cooling capacity of the cooling tower utilizingwindbreakers and the oblique exit plane was predicted as 98.3% of the design value in the presence ofgenerally studied wind velocity profile of 10 m/s, while that of the cooling tower utilizing windbreakerswas predicted as 93.5%. Of course, the percentage of the thermal improvements of the different restoringstrategies are sensitive to the profile of an approaching wind. The uniform wind velocity decreases thethermal efficiency of the cooling tower more than the distributed one, while the restoring strategies usingwindbreakers provide a higher percentage of thermal improvements in the presence of uniform windvelocity.
Cooling Tower
Crosswind
Windbreaker
Oblique exit plane
Cooling efficiency
2017
06
01
39
48
https://ajme.aut.ac.ir/article_971_d95243ea0e02bde5b2b3be48e1122ebb.pdf
AUT Journal of Mechanical Engineering
AJME
2588-2945
2588-2945
2017
1
1
Investigation of Effective Parameters on a Thermal Load in a Thermo-Acoustic Refrigerator
A.
Mohammadi
S. M. A.
Alavi
This article aims to investigate the effects of various parameters on the thermal load. The governing equations include continuity and Navier-Stokes equations for the flow field and the energy equation for the temperature distribution in transient mode. Numerical simulation of the thermoacoustic refrigerator by taking the non-zero thickness of the plate stack into account, that is a conjugate heat transfer problem, in a form of 2D has been performed in FLUENT software. Real simulation of thermoacoustic refrigerators needs a consideration of both heat exchangers, whereas in most simulations one or both heat exchangers have been neglected. Results are influenced by the steady state. Input dynamic pressure should be adjusted according to the temperature of the heat exchanger. The results demonstrate the effect of the distance of the plates on the average thermal load suggesting that the distance between the plates should be four times of the thickness of the plates so that the device works properly. By increasing the distance of the plates thermal load decreases. This is mainly because of pressure amplitude reduction induced by an increase in the distance between the plates.
Refrigerator
Thermo-acoustic
Distance
Plate stack
Thermal load
2017
06
01
49
54
https://ajme.aut.ac.ir/article_782_7e233158f1ae829b07ef5071fa273520.pdf
AUT Journal of Mechanical Engineering
AJME
2588-2945
2588-2945
2017
1
1
A Geometric Modeling Approach to Find the Best Microstructure for Infiltrated SOFC Electrodes
M.
Tafazoli
M.
Shakeri
M.
Baniassadi
A.
Babaei
In this study, a novel design paradigm is presented to obtain some geometry-related electrochemical and physical properties of an infiltrated SOFC electrode. A range of digitally realized microstructures with different backbone geometric properties and virtual electro-catalyst particle loadings under various deposition conditions are generated. Triple Phase Boundary (TPB), the active surface density of particles and gas transport factor are evaluated in those realized models based on selected infiltration strategy. Based on this database, a neural network is trained to relate the desired range of input geometric parameters to a property hull. The effect of porosity and geometric anisotropy in backbones in addition to the loading, distribution and aggregation behavior of particles is systematically investigated on those performance indicators. The results indicated that microstructures with very high amount of TPB and contact surface density of particle have a relatively low gas diffusion factor, meanwhile increasing these parameters does not involve a sensible contradiction. Also, by adding particles, the TPB density variation is changed as a function of backbone porosity and the average shape of aggregated particles. A direct search into the microstructure and property hull is applied to find the best parameters in modeling approach aiming the maximum effective geometric properties. Finally, a genetic algorithm is employed to detect appropriate geometric factors getting the maximum acquirable performance in infiltrated SOFC electrodes.
Microstructure optimization
Infiltrated electrode
Realization of Microstructure
Solid oxide fuel cell
2017
06
01
55
66
https://ajme.aut.ac.ir/article_970_4491c7020bf3e012bf9ea71ba6acd588.pdf
AUT Journal of Mechanical Engineering
AJME
2588-2945
2588-2945
2017
1
1
Improving the Transient Thermal Fatigue Life of a Gas Turbine Casing by Drilling Stop Holes and Inserting Pins into Them
H.
Bazvandi
E.
Poursaeidi
Gas turbines casings are susceptible to cracking at the edge of the eccentric pin hole. Thispaper describes the improvement of the transient thermal fatigue life of gas turbines casings through theapplication of pins. The repair technology under consideration involved drilling a number of holes inthe gas turbines casing along the crack and inserting pins into them. The crack position and directionwere determined using non-destructive tests. A series of finite element models were developed andtested in AStM-A395 elastic-perfectly plastic ductile cast iron. In some specimens, holes were drillednear the crack tips. Pins were inserted into the holes in some cases. Abaqus software finite elementpackage and Zencrack fracture mechanics code were used for modeling. The efficiency of crack repairby the installation of pins was investigated along with the effect of the number of pins on crack repairefficiency. The result shows that the insertion of pins into holes drilled in the vicinity of the crack tips isan effective method of retarding crack growth in a gas turbine casing.
Transient thermal fatigue life
Gas turbine casing
Crack growth retardation
2017
06
01
67
74
https://ajme.aut.ac.ir/article_884_50da32c479f0c0c91fd833f089ffbc46.pdf
AUT Journal of Mechanical Engineering
AJME
2588-2945
2588-2945
2017
1
1
Effect of Viscoelastic Interfaces on Thermo-Mechanical Behavior of a Layered Functionally Graded Spherical Vessel
A.
Talezadehlari
A.
Nikbakht
M.
Sadighi
H.
Yademellat
In layered structures, the interface of layers is not always perfect and the analysis ofproblems which have imperfect interfaces is of the high level of importance. In this paper, an analyticalapproach is used to study the behavior of a layered functionally graded spherical vessel under thermaland mechanical loadings at the inner and outer surfaces. The interfaces of the layers in the vessel areconsidered to be imperfect and a viscoelastic layer of negligible thickness is assumed between anytwo layers. The behavior of these viscoelastic layers is modeled by means of Kelvin-Voigt model. Inorder to solve the problem, the governing equations of each layer are extracted via the thermoelasticitytheory and by applying the appropriate boundary conditions at the interface of the layers, the overalldisplacement and stress fields are found in the vessel and numerical results are presented for differentparameters. The obtained results show that the stiffness of the viscoelastic layer affects the value of thedisplacements and the stresses as well as the stabilization time of the system. However, changing thedamping parameter of the Kelvin-Voigt model only changes the stabilization time and not the values ofthe displacements and stresses.
Spherical vessel
Functionally graded material
Viscoelastic Interface
Mechanical Loading
Thermal Loading
2017
06
01
75
88
https://ajme.aut.ac.ir/article_744_6756f7e08dbeccdf239e24c31d7d1ef3.pdf
AUT Journal of Mechanical Engineering
AJME
2588-2945
2588-2945
2017
1
1
Investigation of Die Clearance in Rubber Pad Forming of Metallic Bipolar Plates
M.
Elyasi
F.
Ahmadi Khatir
M.
Hosseinzadeh
In this research, rubber pad forming process of metallic bipolar plates made of stainlesssteel 316L with a thickness of 0.1 mm has been studied. In addition, a rubber pad made of polyurethanewith the hardness number of shore A 85 and a thickness of 25mm is used in order to apply pressure tothe plate to form the sheets. In order to study the effect of die clearance on depth filling, two die sets withdifferent clearances were made. The results showed that when clearance is applied between punch dieand matrix, the amount of uniformity becomes more in the depth of stuffed channel. But, the rubber padis destroyed after some forming operation and plastic deformation occurs in it. Also, in the die set withthe lower clearance, the amount of rubber pad life has been increased and the amount of flow channeldepth gets greater. In the research results, it was determined that when the channel depth is small and arubber pad is used with a higher hardness, the die set with a clearance has more favorable results due touniformity in the flow channels’ depth. However, by increasing the depth of bipolar plate channels, usingdie sets with lower clearance are better due to the increasing the rubber pad life.
Fuel Cell
Bipolar plate
Rubber pad forming
Die clearance effect
2017
06
01
89
98
https://ajme.aut.ac.ir/article_719_712bd228479c0a1facf293133da2be05.pdf
AUT Journal of Mechanical Engineering
AJME
2588-2945
2588-2945
2017
1
1
An Investigation of the Effects of Crack on the Zone of Pull-in Suppression in MicroElectromechanical Systems Using High-Frequency Excitation
R.
Hassannejad
Sh.
Amiri Jahed
In this paper, the pull-in phenomenon is suppressed using a range of values of amplitudeand frequency of high-frequency voltage excitations in the post pull-in condition of the cracked microelectromechanical systems. These specified ranges are named as stable zones. It is investigated the effects of the crack parameters (depth and location) on changes of these zones, in the post pull-in condition. It is shown that these zones have different areas for different crack parameters. The cracked micro-beam ismodeled as a single-degree-of-freedom systems consist of mass-spring-damper and the motion equationof the cracked micro-beam is extracted. The method of direct partition of motion is used to split the fastand slow dynamics. By means of slow dynamic part, the effects of the crack on the averaged position ofvibration of cracked micro-beam are investigated versus voltage amplitude and frequency of the highfrequency AC. By approaching the crack to the fixed end or increasing the depth of crack, the stabilityzone reduced. Therefore, the pull-in instability can be suppressed in the lower range of amplitude andfrequency. This method can be used in sensors’ health-monitoring and one can predict the parameters ofthe crack using this method.
Micro-beam
Crack
High frequency voltage excitation
Suppression of pull-in phenomenon
Stability zone
2017
06
01
99
108
https://ajme.aut.ac.ir/article_803_45d122f65452bb479b3a85861b584dee.pdf
AUT Journal of Mechanical Engineering
AJME
2588-2945
2588-2945
2017
1
1
Modeling Behavior of a Chain of Protein as a Bionanorobot by Changing Environmental Condition
A.
Gaffari
A.
Khodayari
Sh.
Movasagh
In this paper, the behavior of one chain of small heat shock protein based on molecular dynamic simulation is modeled by the nonlinear identifier. Molecular dynamic simulation is timeconsuming due to the high load of calculations, and providing a model of system behavior facilitates utilizing protein as a bio nano robot in a shorter time. The ARC1 is a molecular Chaperone with swarm structure containing 12 chains. Each chain of small heat shock protein contains two sections; arm and the central cavity which is introduced as a bionanorobot for their special biological structure and their reaction to external forces. The conformational changes of protein with one chain due to external excitation have been analyzed. In addition to system identification of one chain of small heat shock protein, the eﬀect of temperature, pH, and content of solvent are examined on the behavior of bionanorobot arm and a central cavity in a wide range of variation. The results show that minimum number of error is relevant to the adaptive neuro fuzzy system identifier. Modeling the behavior of one chain provides a suitable condition to control the central cavity and bionanorobot arm in a shorter period of time compared to the molecular dynamic simulation.
Chaperone protein
Bionanorobot
GROMACS
Molecular dynamic
Nonlinear identifier
2017
06
01
109
116
https://ajme.aut.ac.ir/article_757_0e1a154c8ca725330c2a6a69c66403b5.pdf