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Numerical simulation of confined nano-impinging jet in microscale cooling application using DSMC method
, Article ASME 2010 8th International Conference on Nanochannels, Microchannels, and Minichannels Collocated with 3rd Joint US-European Fluids Engineering Summer Meeting, ICNMM2010, 1 August 2010 through 5 August 2010, Montreal, QC ; Issue PARTS A AND B , 2010 , Pages 359-366 ; 9780791854501 (ISBN) ; Akhlaghi, H ; Karchani, A ; Schneider, G. E ; Sharif University of Technology
2010
Abstract
In this study, we simulate rarefied gas flow through a confined nano-impinging jet using direct simulation Monte Carlo (DSMC) method. The effects of geometrical parameters, pressure ratio, and wall conditions on the heat transfer from a hot surface are examined. Hot surface modeled via diffusive constant wall temperature. Various inlet/confining surface conditions such as specular, adiabatic, and constant temperature are implemented and the effects of them on the wall heat flux rates are studied. The results show that Knudsen number, velocity slip, and temperature jump are main reasons which specify magnitudes of wall heat flux rates. Among all geometrical parameters, H/W ratio has the...
First and second law analysis of fluid flow in the regenerator of pulse tube refrigerators
, Article 2010 14th International Heat Transfer Conference, IHTC 14, 8 August 2010 through 13 August 2010, Washington, DC ; Volume 4 , 2010 , Pages 247-255 ; 9780791849392 (ISBN) ; Saidi, M. H ; Jafarian, A ; Imanimehr, F ; Asadi, M ; Sharif University of Technology
2010
Abstract
The objective of the present work is to analyze the performance of the regenerator of pulse tube refrigerators. Hydrodynamic and thermal behavior of the regenerator is investigated in this respect. To consider the system performance, a system of conservation equations including two energy equations for the regenerator as a porous media is employed. The present model considers one dimensional periodic unsteady compressible flow in the regenerator. The conservation equations are transformed by implementing the volumetric average scheme. Method of harmonic approximation is employed to derive an analytical solution. To explore the system performance, net energy flow and entropy generation...
Experimental investigation of pulsating heat pipes and a proposed correlation
, Article Heat Transfer Engineering ; Volume 31, Issue 10 , Oct , 2010 , Pages 854-861 ; 01457632 (ISSN) ; Arabnejad, S ; Saboohi, Y ; Jamshidi, H ; Sharif University of Technology
2010
Abstract
Pulsating heat pipes are complex heat transfer devices, and their optimum thermal performance is largely dependent on different parameters. In this paper, in order to investigate these parameters, first a closed-loop pulsating heat pipe (CLPHP) was designed and manufactured. The CLPHP was made of copper tubes with internal diameters of 1.8 mm. The lengths of the evaporator, adiabatic, and condenser sections were 60, 150, and 60 mm, respectively. Afterward, the effect of various parameters, including the working fluid (water and ethanol), the volumetric filling ratio (30%, 40%, 50%, 70%, 80%), and the input heat power (5 to 70 W), on the thermal performance of the CLPHP was investigated...
Three dimensional numerical investigation of air flow over domed roofs
, Article Journal of Wind Engineering and Industrial Aerodynamics ; Volume 98, Issue 3 , 2010 , Pages 161-168 ; 01676105 (ISSN) ; Bahadori, M. N ; Sharif University of Technology
2010
Abstract
Domed roofs have been used in Iran and many other countries to cover large buildings such as mosques, shrines, churches, schools, etc. However their favorable thermal performance made them to be employed in other buildings such as bazaars, or market places, in Iran. The aim of this study was to determine the air pressure distribution over domed roofs, employing a numerical method. In this investigation, a three-dimensional model and a laminar inlet air flow were considered. The k-ε RNG method was employed for the turbulent flow simulation method. Simulation was run under three conditions of windows and a hole on top of the dome being open, or closed. The results were compared with the...
Investigation of weld pool in aluminum alloys: geometry and solidification microstructure
, Article International Journal of Thermal Sciences ; Volume 49, Issue 5 , 2010 , Pages 809-819 ; 12900729 (ISSN) ; Serajzadeh, S ; Kokabi, A. H ; Sharif University of Technology
Abstract
In the present research, weld pool geometry, thermal cycle, temperature and velocity fields during gas tungsten arc welding of aluminum alloys were predicted by solving three-dimensional equations of conservation of mass, energy and momentum under steady-state conditions. Welding experiments were then conducted on several samples with different thicknesses and chemical compositions. The geometries of the weld pools as well as the thermal cycles were measured. It is found that the calculated geometry of the weld fusion zone and the weld thermal cycles are in good agreement with the corresponding experimental results. In addition, the magnitude of the maximum velocities under different...
Numerical study of forced convective heat transfer of nanofluids: comparison of different approaches
, Article International Communications in Heat and Mass Transfer ; Volume 37, Issue 1 , 2010 , Pages 74-78 ; 07351933 (ISSN) ; Saboohi, Y ; Rashidi, A. M ; Sharif University of Technology
Abstract
Forced convective of a nanofluid that consists of water and Al2O3 in horizontal tubes has been studied numerically. Computed results were validated with existing well established correlation. Two-phase Eulerian model has been implemented for the first time to study such a flow field. A single-phase model and two-phase mixture model formulations were also used for comparison. The comparison of calculated results with experimental values shows that the mixture model is more precise. It is illustrated that the single-phase model and the two-phase Eulerian model underestimates the Nusselt number. Effects of nanoparticles concentration on the thermal parameters are also discussed
Control of thermo magnetic heat transfer in porous cavity with Baffle(s)
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings, 13 November 2009 through 19 November 2009 ; Volume 9, Issue PART A , 2010 , Pages 627-631 ; 9780791843826 (ISBN) ; Davoudi, M ; Pirmohammadi, M ; Sharif University of Technology
Abstract
Steady, laminar, natural-convection flow in the presence of a magnetic field in a porous cavity heated from left wall sinusoidally and cooled from right wall is considered. It is well known that unavoidable hydrodynamic movements can be damped with the help of a magnetic field. The Finite Volume method and SIMPLE algorithm for discretizing is used to solve the non-dimensional governing equations. The Convection and Diffusion term of the equations are discretized by Central Difference Scheme (CDS).The numerical procedure has been done over a range of Rayleigh number, Ra, and value of Hartmann number (Ha), 0 ≤ Ha ≤ 150 and effect of them is investigated on average and local Nusselt number....
Boundary control of temperature distribution in a rectangular FGM plate
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings, 13 November 2009 through 19 November 2009, Lake Buena Vista, FL ; Volume 10, Issue PART B , 2010 , Pages 777-783 ; 9780791843833 (ISBN) ; Gharib Shirangi, M ; Eghtesad, M ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2010
Abstract
In this paper an analytical method and a PDE-based solution to control temperature distribution in FGM plates is introduced. For the rectangular FGM plate under consideration, it is assumed that the material properties such as thermal conductivity, density, and specific heat capacity, vary in the width direction (y); and the governing heat conduction equation of the plate is a second-order partial differential equation. Since there has been little control synthesis work for PDE-based systems as compared to the abundance of control design techniques available for ordinary differential equations (ODEs), most of the proposed control approaches for continuous domain rely on discretizing the PDE...
Design, analysis, and implementation of extra low air-gap single-phase axial-flux induction motors for low-cost applications
, Article International Transactions on Electrical Energy Systems ; Volume 26, Issue 12 , 2016 , Pages 2516-2531 ; 20507038 (ISSN) ; Nasiri Gheidari, Z ; Lesani, H ; Sharif University of Technology
John Wiley and Sons Ltd
Abstract
In this paper, design and prototyping of two-speed capacitor-run single-phase axial-flux induction motor (AFIM) for direct-drive applications is presented. The proposed structure has single stator-single rotor configuration with high magnetic pull between the stator and rotor, which may compel rotor to lock. Although the most efficient method to overcome this problem is using a second rotor or stator in the mirror with the first one, it is not applicable in low-cost applications. So, in this paper, two new and fast construction techniques are proposed to fabricate an AFIM with extra low air-gap length and minimum cost. Beside design and optimization process, a thermal equivalent circuit...
CFD modeling of natural convection heat transfer of TIO2-water nanofluid in a cylindrical container
, Article Frontiers in Heat and Mass Transfer ; Volume 7, Issue 1 , 2016 ; 21518629 (ISSN) ; Sharif University of Technology
Global Digital Central
Abstract
This work focuses on numerical validation of natural convection heat transfer of TiO2-water nanofluids in a cylindrical container using COMSOL. The main aim of this study is to examine different available approaches to calculate effective thermal conductivity and compare them with experimental data available in the literature. Simulation results show that for considered mixture, average Nusselt number decreases by increasing Rayleigh number and particle volume fraction. It has been found that only one model was able to represent similar trends for given particle volume fractions, compared to experimental results
Part load behavior of molten salt cavity receiver solar tower plants under storage mode operational mode
, Article ASME 2016 10th International Conference on Energy Sustainability, ES 2016, collocated with the ASME 2016 Power Conference and the ASME 2016 14th International Conference on Fuel Cell Science, Engineering and Technology, 26 June 2016 through 30 June 2016 ; Volume 1 , 2016 ; 9780791850220 (ISBN) ; Shafiei Ghazani, A ; Taylor, R. A ; Saberi, P ; Sharif University of Technology
American Society of Mechanical Engineers
2016
Abstract
The performance of the tower based concentrated solar thermal (CST-tower) plant is very sensitive to the operation strategy of the plant and the incident heat flux on the receiver. To date, most studies have been examined only the design mode characteristics of the cavity receivers, but this paper significantly expands the literature by considering non-design operating conditions of this important sub-component of the CST-tower plants. A feasible non-design operating conditions of the cavity receivers that was considered in this study is the storage mode of operation. Two practical dynamic control strategies were examined then to find the most efficient approach: fixed solar field mass...
The effect of soot nano-particles injection on two-phase smoke aerosol formation in a kerosene-fired burner
, Article 54th AIAA Aerospace Sciences Meeting, 2016, 4 January 2016 through 8 January 2016 ; 2016 ; 9781624103933 (ISBN) ; Ghafourizadeh, M ; Schneider, G. E
American Institute of Aeronautics and Astronautics Inc, AIAA
Abstract
Feeding a laboratory furnace with the gaseous kerosene, the resulting two-phase turbulent flame is simulated to study the effects of injecting soot nano-particles into the inflow air on the emissions of smoke aerosol, CO, and CO2species pollutants, and the resulting radiation heat transfer. We use our past experiences in aerosol modeling of soot nano/micro particles in turbulent nonpremixed flames burning simple hydrocarbon fuels and extend them to study the effects of injecting gaseous kerosene on the aforementioned parameters. To model the evolutionary process of soot nanoparticle formation, i.e., the nucleation, coagulation, surface growth, and oxidation, we employ a two-equation soot...
The effects of baffle plate on soot nano-aerosol and pollutant productions in a JP-fueled combustor
, Article 54th AIAA Aerospace Sciences Meeting, 2016, 4 January 2016 through 8 January 2016 ; 2016 ; 9781624103933 (ISBN) ; Ghafourizadeh, M ; Schneider, G. E ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc, AIAA
2016
Abstract
In this paper, the effects of a baffle plate on flame deflection and its throttling are investigated numerically in a combustor consuming jet propellant JP. We study the plate effects on the resulting soot volume fraction, soot particles diameter, mass fractions of carbon monoxide (CO), carbon dioxide (CO2), and benzene (C6H6). We use a two-equation turbulence model, a PAH-inception two-equation soot model imposing oxidation due to OH agents, a detailed chemical kinetic consisting of 121 species and 2613 elementary reactions, and the flamelet combustion model to perform the current study. We also take into account the turbulence-chemistry interaction using the presumed-shape probability...
A numerical study on the absorption of water vapor into a film of aqueous LiBr falling along a vertical plate
, Article Heat and Mass Transfer/Waerme- und Stoffuebertragung ; Volume 46, Issue 2 , 2009 , Pages 197-207 ; 09477411 (ISSN) ; Farhanieh, B ; Sharif University of Technology
Abstract
Absorber is an important component in absorption machines and its characteristics have significant effects on the overall efficiency of absorption machines. This article reports a model of simultaneous heat and mass transfer process in absorption of refrigerant vapor into a lithium bromide solution of water - cooled vertical plate absorber in the Reynolds number range of 5 < Re < 150. The boundary layer assumptions were used for the transport of mass, momentum and energy equations and the fully implicit finite difference method was employed to solve the governing equations in the film flow. Dependence of lithium bromide aqueous properties to the temperature and concentration and film...
Experimental investigation of closed loop pulsating heat pipe with nanofluids
, Article Proceedings of the ASME Summer Heat Transfer Conference 2009, HT2009 ; Volume 1 , 2009 , Pages 675-683 ; 9780791843567 (ISBN) ; Arabnejad, S ; Behshad Shafii, M ; Saboohi, Y ; Rasoulian, R ; Sharif University of Technology
Abstract
In this paper, the effect of several different parameters on the thermal resistance of a Closed Loop Pulsating Heat Pipe (CLPHP) has been investigated. These parameters include the working fluid, the inclination angle, the filling ratio and the heat influx. Also, the impact of using nanofluids with different nano-particle concentrations has been analyzed. It was observed that a CLPHP can increase the heat transfer up to 11.5 times compared to an empty pipe. Optimum performance for a system with the water-silver nanofluid was achieved at conditions of 50% filling ratio and 0.9 K/W of thermal resistance, and for the water-titanium oxide system, these optimal conditions were found to be 40%...
Analytical solution of chamber effective length in the axial engine
, Article Proceedings of the ASME Fluids Engineering Division Summer Conference 2009, FEDSM2009, 2 August 2009 through 6 August 2009, Vail, CO ; Volume 1, Issue PART B , 2009 , Pages 881-888 ; 9780791843727 (ISBN) ; Mozafari, A. A ; Saidi, M. H ; Ghafourian, A ; Sharif University of Technology
Abstract
In this research, effective length of one-dimensional combustion in a dilute monopropellant spray, constant area and fixed volume chamber is analytically predicted. A new evaporation rate in the form of d k+1 relation is introduced. In the case of controlling vaporization by radiative heat transfer, k is equal to zero, and when molecular processes control the vaporization, k will be equal to one and in some cases vaporization data need the value of k greater than one to fit properly to related equation. Development of this approach can be used in the design of combustion chambers with optimum length and with using vaporization rate of R = R0〈r〉 0 k/〈r〉k. Spray equation and distribution...
Mixed convection cooling of a heated circular cylinder by laminar upward-directed slot jet impingement
, Article Heat and Mass Transfer/Waerme- und Stoffuebertragung ; Volume 46, Issue 2 , 2009 , Pages 225-236 ; 09477411 (ISSN) ; Habibi, K ; Faghani, E ; Ashjaee, M ; Sharif University of Technology
Abstract
An experimental and numerical study has been carried out to investigate the heat transfer characteristics of a horizontal circular cylinder exposed to a slot jet impingement of air. A square-edged nozzle is mounted parallel with the cylinder axis and jet flow impinges on the bottom of the cylinder. The study is focused on low Reynolds numbers ranging from 120 to 1,210, Grashof numbers up to Gr = 10Re2 and slot-to-cylinder spacing from 2 to 8 of the slot width. The flow field is greatly influenced by the slot exit velocity and the buoyancy force due to density change. A Mach-Zehnder Interferometer is used for measurement of local Nusselt number around the cylinder at 10° interval. It is...
Numerical study of turbulent nanofluid heat transfer in a tubular heat exchanger with twin twisted-tape inserts
, Article Journal of Thermal Analysis and Calorimetry ; 2017 , Pages 1-19 ; 13886150 (ISSN) ; Akbari, O. A ; Hassanzadeh Afrouzi, H ; Biglarian, M ; Koveiti, A ; Toghraie, D ; Sharif University of Technology
Abstract
In the present study, the turbulent flow of water/Al2O3 nanofluid in a tubular heat exchanger with two twisted-tape inserts has been numerically investigated in the three-dimensional coordinate. This numerical simulation has been done by using FVM, and all of the equations have been discretized by second-order upwind method. For coupling velocity–pressure equations, SIMPLEC algorithm has been used. The investigated parameters of the present study are Reynolds numbers at the range of 10,000–30,000, the effect of twist ratio of twisted-tape inserts from 2.5 to 4, co-swirl flow and counter-swirl flow of two twisted-tapes inside the tube and volume fractions of nanofluid from 1 to 4%. The...
Second law analysis of an infinitely segmented magnetohydrodynamic generator
, Article Journal of Magnetism and Magnetic Materials ; Volume 426 , 2017 , Pages 294-301 ; 03048853 (ISSN) ; Saidi, M. H ; Najafi, M ; Sharif University of Technology
Elsevier B.V
2017
Abstract
The performance of an infinitely segmented magnetohydrodynamic generator is analyzed using the second law of thermodynamics entropy generation criterion. The exact analytical solution of the velocity and temperature fields are provided by applying the modified Hartmann flow model, taking into account the occurrence of the Hall effect in the considered generator. Contributions of heat transfer, fluid friction, and ohmic dissipation to the destruction of useful available work are found, and the nature of irreversibilities in the considered generator is determined. In addition, the electrical isotropic efficiency scheme is used to evaluate the generator performance. Finally, the implication of...
A modified turbulent heat-flux model for predicting heat transfer in separating-reattaching flows and film cooling applications
, Article Applied Thermal Engineering ; Volume 110 , 2017 , Pages 1609-1623 ; 13594311 (ISSN) ; Chaharlang Kiani, K ; Karimi, M ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
The present study addresses a new effort to improve the prediction of the thermal field in separating-reattaching flows by making modifications in a low-Reynolds-number (LRN) version of HOGGDH heat-flux model proposed by Suga and Abe (2000). The modifications are based on introducing non-equilibrium effects of hydrodynamic flow field in the heat-flux model. Using an analytical approach, we have implemented P/ε, ignored in the base version, to the modified version. To do so, the model structure was changed and a damping function which is more sensitive to non-equilibrium flow features is also applied to the model. The modified heat-flux formulation along with a second moment closure...