Search for: temperature-gradient
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    Temperature gradient and wind profile effects on heavy gas dispersion in build up area

    , Article Journal of Applied Sciences Research ; Volume 6, Issue 12 , 2010 , Pages 6010-6020 ; 1816157X (ISSN) Kashi, E ; Shahraki, F ; Rashtchian, D ; Behzadmehr, A ; Sharif University of Technology
    Dispersion of heavy gases is considered to be more hazardous than the passive ones. This is because it takes place more slowly. In this paper, based on the extensive experimental work of Hanna and Chang, the CFD model (Ansys-CFX) was tested compared with Kit Fox experiments. In order to accomplish this validation, the multiphase approach was employed as a new method in this area. In addition, the temperature gradient effects were investigated. The survey of wind speed was done taking factors such as time, height and direction into the consideration. To reduce the number of elements in computational domain, a combination of 2D and 3D geometries were utilized. Results showed that the wind... 

    Temperature gradient and wind profile effects on heavy gas dispersion in build up area

    , Article Australian Journal of Basic and Applied Sciences ; Volume 4, Issue 12 , 2010 , Pages 6010-6020 ; 19918178 (ISSN) Kashi, E ; Shahraki, F ; Rashtchian, D ; Behzadmehr, A ; Sharif University of Technology
    Dispersion of heavy gases is considered to be more hazardous than the passive ones. This is because it takes place more slowly. In this paper, based on the extensive experimental work of Hanna and Chang, the CFD model (Ansys-CFX) was tested compared with Kit Fox experiments. In order to accomplish this validation, the multiphase approach was employed as a new method in this area. In addition, the temperature gradient effects were investigated. The survey of wind speed was done taking factors such as time, height and direction into the consideration. To reduce the number of elements in computational domain, a combination of 2D and 3D geometries were utilized. Results showed that the wind... 

    The densification behavior of metals and alloys during spark plasma sintering: A mini-review

    , Article Science of Sintering ; Volume 51, Issue 2 , 2019 , Pages 1-18 ; 0350820X (ISSN) Sovizi, S ; Esmaeeli Seraji, M ; Sharif University of Technology
    International Institute for the Science of Sintering (IISS)  2019
    As of today, metals and alloys are widely utilized as structural, mechanical, electrical, and magnetic materials in every aspect of technology and industry. The complexity and diversity of metals applications emphasize the need for a new production method to quickly and easily manufacture metallic components. Spark plasma sintering as a new solid-state sintering method has been recently developed to respond to these needs. Up to now, numerous papers and researches have been published in the field of spark plasma sintering and its ability to manufacture metallic samples. Density is a significant property that has a great influence on the physical, mechanical, and functional properties of... 

    Effect of Temperature Gradient on Ultrasonic Flowmeters

    , M.Sc. Thesis Sharif University of Technology Fathi, Shayan (Author) ; Sadrhosseini, H (Supervisor) ; Kazemzadeh Hannani, Siamak (Co-Advisor)
    Ultrasonic flowmeters are one of the common and profitable measurement tools and applied in many industrial fields.Ultrasonic flowmeters work based on transit-time technique. The transit-time utilizes the propagation time of the ultrasonic signal in the fluid. Since ultrasonic signals can also penetrate solid materials, a pair of transducers is installed on the surface of tube. Each transducer works alternatively as both transmitter and receiver of ultrasonic signals.In this study, effect of temperature gradient on flowmeter measurements by applying constant temperature and uniform heat flux on the boundary is investigated numerically for methane gas in laminar flow regime and the results... 

    Investigation of Flow Rate and Cooling Water Temperature Effects on the Process Parameters in Centrifuge Machine

    , M.Sc. Thesis Sharif University of Technology Aghaei, Majid (Author) ; Otukesh, Mohammad (Supervisor) ; Safdari, Jaber (Supervisor)
    Centrifuge is a method in which great gravitational-like forces are used. Gravitational forces which cause molecules to move and are relevant to molecular weight; can cause isotope separation. The separation of light isotope from heavy one is done with a centrifugal field which produces a pressure gradient for the gas mixture. Pressure gradient is different for each of the isotopes due to the dependence of pressure gradient to the mass of the materials. But the separation in this way is very limited. The capacity of separation can be brought up by producing an additional axial flow in the rotor. This rotational flow can be produced with internal or external incitement. Rotational flow with... 

    Numerical experiments with compressible free convection in vertical slots

    , Article 38th AIAA Thermophysics Conference, Toronto, ON, 6 June 2005 through 9 June 2005 ; 2005 ; 9781624100611 (ISBN) Darbandi, M ; Hosseinizadeh, S. F ; Schneider, G. E ; Sharif University of Technology
    American Institute of Aeronautics and Astronautics Inc  2005
    One important heat transfer application in engineering is to predict the flow behavior and heat transfer rate in thin vertical air layers. There are numerous applications in engi- neering where high temperature gradients exist between the slot walls. In such cases, the methods based on simple Boussinesq approximations do not provide reliable predictions. Unfortunately, the compressibility effect in heat transfer rate through thin vertical slots has not been much investigated by the past investigators. In this work, a compressible algorithm is properly developed and utilized to solve compressible natural convection in vertical air layers. The current technique employs discretization equations... 

    Directed motion of C60 on a graphene sheet subjected to a temperature gradient

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 83, Issue 4 , 2011 ; 15393755 (ISSN) Lohrasebi, A ; Neek Amal, M ; Ejtehadi, M. R ; Sharif University of Technology
    Nonequilibrium molecular dynamics simulations are used to study the motion of a C60 molecule on a graphene sheet subjected to a temperature gradient. The C60 molecule is actuated and moves along the system while it just randomly dances along the perpendicular direction. Increasing the temperature gradient increases the directed velocity of C60. It is found that the free energy decreases as the C60 molecule moves toward the cold end. The driving mechanism based on the temperature gradient suggests the construction of nanoscale graphene-based motors  

    Design of spherical vessels under steady-state thermal loading using thermo-elasto-plastic concept

    , Article International Journal of Pressure Vessels and Piping ; Volume 86, Issue 2-3 , 2009 , Pages 143-152 ; 03080161 (ISSN) Darijani, H ; Kargarnovin, M. H ; Naghdabadi, R ; Sharif University of Technology
    Governing equilibrium equations of thick-walled spherical vessels made of material following linear strain hardening and subjected to a steady-state radial temperature gradient using elasto-plastic analysis are derived. By considering a maximum plastic radius and using the concept of thermal autofrettage for the strengthening mechanism, the optimum wall thickness of the vessel for a given temperature gradient across the wall thickness is obtained. Finally, in the case of thermal loading on a vessel, the effect of convective heat transfer on the optimum thickness is studied and a general formula for the optimum wall thickness and design graphs for several different cases are presented. © 2008... 

    Evaluation of the Effect of Temperature Gradient on the Dynamic Behavior of Concrete Arch Dams

    , M.Sc. Thesis Sharif University of Technology Moghaddas Jafari, Reyhaneh (Author) ; Rahim Zadeh Rofooei, Fayyaz (Supervisor)
    Concrete arch dams, because of their special shape as a 3-D huge shell which is fixed from three sides, are very sensitive to temperature and its variation. Therefore, it is required to include the temperature variations and their related thermal stresses and strains in the safety analysis of dams. In this research, the effect of applying the thermal gradients caused by the most critical thermal conditions, on dynamic behavior of concrete arch dams was studied. For this purpose, first a roughly exact 3-D finite element model of Karoon ІV arch dam was prepared by ANSYS program. Then, the temperature distribution through the dam thickness was determined by Stucky-Derron method and in a more... 

    Advances in non-gray radiation calculation in combusting environments using a modified reference approach

    , Article Heat and Mass Transfer/Waerme- und Stoffuebertragung ; Volume 54, Issue 9 , 2018 , Pages 2705-2713 ; 09477411 (ISSN) Darbandi, M ; Abrar, B ; Sharif University of Technology
    Springer Verlag  2018
    The radiative heat transfer should be calculated very accurately in many combustion domains. This work uses the spectral-line based weighted-sum-of-gray-gases (SLW) model to calculate the radiation heat transfer in a model furnace representing a combustion field with high temperature gradient variations. The past researchers have commonly implemented the reference approach in the SLW model. However, the reference approach produces error because of enforcing a reference temperature to perform the non-gray radiation heat transfer calculations in non-isothermal domains. In this work, we implement a modified reference approach, which reduces such errors in non-gray gas calculations. We show that... 

    Directional control of surface rolling molecules exploiting non-uniform heat-induced substrates

    , Article Physical chemistry chemical physics : PCCP ; Volume 22, Issue 46 , 7 December , 2020 , Pages 26887-26900 Nemati, A ; Nejat Pishkenari, H ; Meghdari, A ; Ge, S. S ; Sharif University of Technology
    NLM (Medline)  2020
    Molecular machines, such as nanocars, have shown promising potential for various tasks, including manipulation at the nanoscale. In this paper, we examined the influence of temperature gradients on nanocar and nanotruck motion as well as C60 - as their wheel - on a flat gold surface under various conditions. We also compared the accuracy and computational cost of two different approaches for generating the temperature gradient. The results show that severe vibrations and frequent impacts of gold atoms at high temperatures increase the average distance of C60 from the substrate, reducing its binding energy. Moreover, the temperature field drives C60 to move along the temperature variation;... 

    Computational analysis of injection-velocity effects on dynamic parameters of unconfined fuel-vapor clouds

    , Article Combustion, Explosion and Shock Waves ; Volume 41, Issue 5 , 2005 , Pages 510-520 ; 00105082 (ISSN) Doustdar, M. M ; Mazaheri, K ; Hosseinalipour, M ; Sharif University of Technology
    A computational investigation is performed to study the effects of injection velocity on the main dynamic parameters of the fuel cloud released into the open atmosphere. The volume, shape, and growth rate of the cloud, turbulence intensity, as well as the distribution of fuel concentration, temperature gradient, and self-ignition induction time are the most important parameters determining the mode of combustion that propagates through the cloud. A modified KIVA-based program is employed to fulfill the calculations. Systems of equations are solved by a finite-volume method. The k-ε model and discrete droplet model are applied for modeling gas-phase turbulence and liquid spray, respectively.... 

    Solving combined natural convection-radiation in participating media considering the compressibility effects

    , Article 52nd AIAA Aerospace Sciences Meeting - AIAA Science and Technology Forum and Exposition, SciTech 2014 ; 13- 17 January , 2014 ; ISBN: 9781624102561 Darbandi, M ; Abrar, B ; Schneider, G. E ; Sharif University of Technology
    In this work, we aim to study the effect of temperature gradients on the combined natural convection-radiation heat transfer problem in participating media. To impose this combined effect, we first solve the radiative transfer equation in an absorbing and emitting media. Then, we suitably add the radiation source terms to the energy equation and solve the fluid flow equations. Literature shows that many incompressible algorithms use the Boussinesq assumption to model the thermobuoyant force; however, the validity of this assumption is limited to cases with low temperature gradient distributions. Evidently, Boussinesq assumption would result in considerable errors in high temperature gradient... 

    Frequency characteristics of FG-GPLRC viscoelastic thick annular plate with the aid of GDQM

    , Article Thin-Walled Structures ; Volume 150 , 2020 Safarpour, M ; Ghabussi, A ; Ebrahimi, F ; Habibi, M ; Safarpour, H ; Sharif University of Technology
    Elsevier Ltd  2020
    This is the first research on the free vibration analysis of functionally graded graphene platelets reinforced composite (FG-GPLRC) viscoelastic annular plate resting on the visco-Pasternak foundation and subjected to the nonlinear temperature gradient and mechanical loading within the framework of higher-order shear deformation theory (HSDT). Hamilton's principle is employed to establish governing equations within the framework of HSDT. In this paper, viscoelastic properties are modeled according to Kelvin-Voigt viscoelasticity. The deflection as the function of time can be solved by the fourth-order Runge-Kutta numerical method. Generalized differential quadrature method (GDQM) is applied... 

    Elasto-Plastic Design of Thick-Walled FG Vessels under Pressure or Temperature Gradient Loadings

    , M.Sc. Thesis Sharif University of Technology Mansoupour Bonab, Hojjat (Author) ; Kargarnovin, Mohammad Hossein (Supervisor)
    Nowadays functionally graded materials have many applications in various industries. One of these applications can be the manufacturing of thick-walled vessels. Thick-walled vessels under internal pressure and high temperatures gradient require materials with higher strength, like Functionally Graded Materials (FGM) and can be reinforced by some mechanical processes like autofrettage. In this process under certain loading some part of vessels enters into plastic zone and upon unloading some residual stresses will be generated. Moreover it is very important to find out the depth of this plastic zone, In addition, minimizing the stress distribution vs. depth of plastic zone under applied... 

    Transient Liquid phase Bonding of AL2024 Alloy and Evaluation of Joint Properties

    , Ph.D. Dissertation Sharif University of Technology Mahmoodi Ghaznavi, Majid (Author) ; Kokabi, Amir Hossein (Supervisor) ; Ekrami, Ali Akbar (Supervisor)
    Transient liquid phase (TLP) bonding of Al2024-T6 alloy, using gallium interlayer, has been investigated. Bonding experiments were carried out using two basic methods; Conventional and Temperature gradient TLP bonding. Optimum values of isothermal solidification temperature and time, pressure, surface roughness, heating rate and homogenizing conditions were determined in conventional TLP bonding experiments. Aluminum oxide layer was not removed before TLP bonding to prevent gallium attack.this layer is crashed during bonding. Al2O3 particles are not soluble in the liquid and are pushed into liquid by solidification front progression. These particles are accumulated in grain boundaries and in... 

    thermo-Elasto-Plastic Analysis of Spherical and Cylindrical FG Reservoirs Subjected to Temperature Gradient and Internal Pressure Loading

    , M.Sc. Thesis Sharif University of Technology Heydari, Abbas (Author) ; Kazemi, Mohammad Taghi (Supervisor)
    Design of thick-walled spherical and cylindrical vessels as fluids containers of high gradient thermal loading is a challenging issue. Using these tanks in high pressure and temperature gradient, particularly in chemical industries, needs to use new methods in design. Elasto-Plastic solution for thick-walled hollow spherical and cylindrical tanks made of FG materials subjected to internal pressure and temperature loading is presented. The power law modeling is used for through-the-thickness variation of mechanical properties. This method is using the new advanced materials with high pressure and thermal strength in fabricating these vessels. One of these materials is functionally graded (FG)... 

    Using the direct simulation Monte Carlo method to study the effect of wall temperature variation on gas mixing evolution through micro T-mixers

    , Article 11th International Energy Conversion Engineering Conference ; 2013 Darbandi, M ; Sabouri, M ; Lekzian, E ; Schneider, G. E ; Sharif University of Technology
    In this work, we study the gas mixing behavior in a micro T-mixer using the direct simulation Monte Carlo (DSMC) method. The gas mixing process is monitored through a T-mixer, which is fed by two different CO and N2 gases; flowing into the T-mixer through the upper and lower inlets. We investigate the effects of axial and lateral wall temperature gradients on the mixing evolution at different rarefaction levels. The achieved results show that any temperature difference between the channel walls would result in an increase in mixing length for the chosen wall temperature gradient ranges and the studies pressure cases. Our observations show that a positive temperature gradient toward the... 

    High gradient temperature thermo-buoyant flow in a square cavity with magnetoconvection using a novel non-boussinesq algorithm

    , Article Numerical Heat Transfer; Part A: Applications ; Volume 64, Issue 3 , 2013 , Pages 255-272 ; 10407782 (ISSN) Hosseinizadeh, S. F ; Hajibagheri, M ; Heidarnataj, M ; Darbandi, M ; Javaherdeh, K ; Sharif University of Technology
    We study numerically the heat transfer of steady laminar flow in a square cavity filled with electrically conducting fluids, in the presence of an external uniform magnetic field. Imposing a large temperature gradient between two opposite vertical walls, there are substantial temperature and density variations in the domain. The fluid is treated as an ideal gas. Indeed, high temperature gradient thermo-buoyant cavity flows result in natural convection flow domains with high Rayleigh number. To implement the temperature variation effect, the fluid properties, including the conductivity and viscosity coefficients, are considered to vary with temperature in accordance to the Sutherland's law.... 

    Design and optimization of a cascade thermoacoustic Stirling engine

    , Article Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy ; Volume 227, Issue 7 , September , 2013 , Pages 814-824 ; 09576509 (ISSN) Karimi, M ; Ghorbanian, K ; Sharif University of Technology
    Professional Engineering Publishing  2013
    This article deals with the design and optimization of a cascade thermoacoustic Stirling engine. Different configurations for cascade thermoacoustic Stirling heat engine are investigated. A simplified model is proposed to enable initial design guidelines. The most important characteristics of the cascade system are examined. The results indicate that the thermoacoustic engines in cascade configuration may achieve very low onset temperatures. A suitable configuration is selected and the locations and dimensions of different thermoacoustic units are optimized to achieve low onset temperatures as well as high values for the acoustic power output and efficiency. The results support the...