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Linear analysis of the stability of particle-laden stratified shear layers
, Article Canadian Journal of Physics ; Vol. 92, issue. 2 , 2014 , pp. 103-115 ; ISSN: 00084204 ; Firoozabadi, B ; Afshin, H
2014
Abstract
Hydrodynamic instabilities at the interface of stratified shear layers could occur in various modes and have an important role in the mixing process. In this work, the linear stability analysis in the temporal framework is used to study the stability characteristics of a particle-laden stratified two-layer flow for two different background density profiles: smooth (hyperbolic tangent) and piecewise linear. The effect of parameters, such as bed slope, viscosity, and particle size, on the stability is also considered. The pseudospectral collocation method employing Chebyshev polynomials is used to solve two coupled eigenvalue equations. Based on the results, there are some differences in the...
Experimental and numerical simulation of the effect of particles on flow structures in secondary sedimentation tanks
, Article Journal of Applied Fluid Mechanics ; Volume 5, Issue 2 , 2012 , Pages 15-23 ; 17353572 (ISSN) ; Firoozabadi, B ; Afshin, H ; Sharif University of Technology
JAFM
2012
Abstract
Sedimentation tanks are designed for removal of floating solids in water flowing through the water treatment plants. These tanks are one of the most important parts of water treatment plants and their performance directly affects the functionality of these systems. Flow pattern has an important role in the design and performance improvement of sedimentation tanks. In this work, an experimental study of particle-laden flow in a rectangular sedimentation tank has been performed. Kaolin was used as solid particles in these experiments. Also, a numerical simulation was developed using the finite volume method with a k-e turbulent model. The results of the numerical model agree well with the...
Experimental investigation of effects of baffle configurations on the performance of a secondary sedimentation tank
, Article Scientia Iranica ; Volume 18, Issue 4 B , August , 2011 , Pages 938-949 ; 10263098 (ISSN) ; Firoozabadi, B ; Afshin, H ; Sharif University of Technology
2011
Abstract
Sedimentation tanks are designed for the settling of floated solids in water. These tanks are one of the most important parts of water treatment plants and their performance directly affects the functionality of these plants. One challenging method for increasing the performance of sedimentation tanks is to use baffles. A useful baffle should be installed in a suitable place with a proper height. In this work, an experimental study of particle-laden flow in a rectangular sedimentation tank has been performed and kaolin is used as solid particles. The effects of baffle configurations on the velocity and concentration profiles along the tank were studied. Sedimentation tank performance was...
Numerical study of heat and mass transfer in underexpanded sonic free jet
, Article International Journal of Heat and Technology ; Volume 35, Issue 4 , 2017 , Pages 959-968 ; 03928764 (ISSN) ; Farhanieh, B ; Afshin, H ; Sharif University of Technology
2017
Abstract
In case of unexpected ruptures in high pressure tanks, choking phenomenon occurs in the cracked area which fluid velocity gets sonic and its pressure exceeds atmospheric pressure. Afterward, pressure of discharged gas quickly changes by crossing through compression and expansion shock waves. The main aim of this study was numerical simulation and investigation of this flow in a 3-step process: (a) Detailed analysis of numerical method, (b) Qualitative and quantitative analysis of velocity, pressure, temperature and turbulence intensity, in order to propose safety strategies and (c) parametric studies on the effects of tank pressure and nozzle geometry on flow structure. In numerical...
Numerical simulation to investigate the induced buoyant flow characteristics caused by intensive heat in complex curvilinear geometries
, Article Heat Transfer - Asian Research ; Volume 48, Issue 3 , 2019 , Pages 835-853 ; 10992871 (ISSN) ; Farhanieh, B ; Afshin, H ; Sharif University of Technology
John Wiley and Sons Inc
2019
Abstract
The buoyancy-induced turbulent flows in complex geometries with internal heat source have important application in enclosure fire dynamics, for example, smoke movement in the situation of fire in tunnels. The majority of computational works studying the fire-induced hot air movement in such cases use a Cartesian coordinate system. Hence, to simulate curved geometries, the Cartesian grid should be refined so that it comparatively matches the geometry. In the present work, a three-dimensional numerical method using nonorthogonal curvilinear coordinate system was developed. Numerical simulations were performed to study the flow structures and the heat transfer characteristics of fire-induced...
Proposing a general formula to calculate the critical velocities in tunnels with different cross-sectional shapes
, Article Tunnelling and Underground Space Technology ; Volume 110 , 2021 ; 08867798 (ISSN) ; Farhanieh, B ; Afshin, H ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
Among the parameters affecting the critical velocity in tunnel fires, the tunnel cross-sectional shape could significantly affect the tunnel fire characteristics, mainly due to the wall-bounded physics of the tunnel fire. Previously, the effects of the cross-sectional geometry of the tunnel were calculated using the non-dimensional analysis and hydraulic height of the tunnel. The dimensionless analysis using hydraulic height calculates only the effects of the tunnel sizes and does not capture the effects of the shape of the tunnel cross-section. Developing a 3D computational fluid dynamics tool using the body-fitted grids, the critical velocities are calculated for the 7 different...
Heat and mass transfer analysis and optimization of freeze desalination utilizing cold energy of LNG leaving a power generation cycle
, Article Desalination ; Volume 527 , 2022 ; 00119164 (ISSN) ; Eghtesad, A ; Afshin, H ; Sharif University of Technology
Elsevier B.V
2022
Abstract
Freeze desalination (FD) works upon the separation of impurities from pure water during ice crystals formation. The required cold source could be supplied by the cold energy of liquefied natural gas (LNG). In the current study, freeze desalination of seawater is explored by directly exploiting the cold energy of LNG within an appropriate range of temperature after producing work in a power generation cycle. A detailed discussion has been given on the inlet temperature of LNG to the FD unit for the first time. The direct utilization has the privilege of eliminating the addition of a secondary refrigerant and its refrigeration cycle to the FD process. A multi-objective optimization is...
Numerical investigation of critical velocity in curved tunnels: Parametric study and establishment of new model
, Article Tunnelling and Underground Space Technology ; Volume 135 , 2023 ; 08867798 (ISSN) ; Farhanieh, B ; Afshin, H ; Sharif University of Technology
Elsevier Ltd
2023
Abstract
Curved tunnels are more likely to have an accident and a fire source due to their physical characteristics. Using a 3D computational fluid dynamics tool with body-fitted grids, three different fire locations were investigated numerically in a series of curved tunnels with a turning radius of 50–1000 m and a heat release rate of 5–15 MW. Results showed that the critical velocity increased with increasing tunnel turning radius, and the straight tunnel had the highest critical velocity in all scenarios. For a tunnel with a 10 MW heat release rate, the critical velocity increased by 19 % from R = 50 to 1000 m. Furthermore, it was shown that the critical velocity was proportional to one-third...
3-D simulation of turbulent density
, Article 2006 ASME Joint U.S.- European Fluids Engineering Division Summer Meeting, FEDSM2006, Miami, FL, 17 July 2006 through 20 July 2006 ; Volume 2 FORUMS , 2006 , Pages 361-367 ; 0791847500 (ISBN); 9780791847503 (ISBN) ; Firoozabadi, B ; Ghasvari Jahromi, H ; Afshin, H ; Sharif University of Technology
American Society of Mechanical Engineers
2006
Abstract
Density current is a dense fluid, which is continuously released from a source and spreads down a sloping surface inside a lighter, motionless fluid. A low-Reynolds number k-ε model (Launder and Sharma, 1974) has been used to simulate the behavior of 3-D density currents. Density current with a uniform velocity and concentration enters the channel via a sluice gate into a lighter ambient fluid and moves forward down-slope. The model has been verified with the experimental data sets. Although the k-ε Launder and Sharma model is applied here to a conservative density current, it seems the analysis is valid in general for turbidity current laden with fine particles. Copyright © 2006 by ASME
Comparison of 2-D turbulent particle laden density current and wall jets
, Article 2006 ASME Joint U.S.- European Fluids Engineering Division Summer Meeting, FEDSM2006, Miami, FL, 17 July 2006 through 20 July 2006 ; Volume 1 SYPMOSIA , 2006 , Pages 1763-1770 ; 0791847500 (ISBN); 9780791847503 (ISBN) ; Firoozabadi, B ; Ghasvari Jahromi, H ; Afshin, H ; Sharif University of Technology
American Society of Mechanical Engineers
2006
Abstract
Dense underflows are continuous currents, which move down the slope due to the fact that, their density are heavier than ambient water. In turbidity currents the density differences arises from suspended solids. Vicinity of the wall make density currents and wall jets similar in some sense but Variation of density cause this flows more complex than wall jets. An improved form of 'near-wall' k-ε turbulence model is chosen which preserve all characteristics of both density and wall jet currents and a compression is made between them. Then the outcomes from low Reynolds number k-ε model is compared with v̄2 - f model which show similarity. Also results show good agreement with experimental data...
3-D simulation of turbulent density
, Article 2006 2nd ASME Joint U.S.-European Fluids Engineering Summer Meeting, FEDSM 2006, Miami, FL, 17 July 2006 through 20 July 2006 ; Volume 2006 , 2006 ; 0791837831 (ISBN); 9780791837832 (ISBN) ; Firoozabadi, B ; Afshin, H ; Ghasvari Jahromi, H ; Sharif University of Technology
2006
Abstract
Density current is a dense fluid, which is continuously released from a source and spreads down a sloping surface inside a lighter, motionless fluid. A low-Reynolds number k-ε model (Launder and Sharma, 1974) has been used to simulate the behavior of 3-D density currents. Density current with a uniform velocity and concentration enters the channel via a sluice gate into a lighter ambient fluid and moves forward down-slope. The model has been verified with the experimental data sets. Although the k-ε Launder and Sharma model is applied here to a conservative density current, it seems the analysis is valid in general for turbidity current laden with fine particles. Copyright © 2006 by ASME
Comparison of 2_D turbulent particle laden density current and wall jets
, Article 2006 2nd ASME Joint U.S.-European Fluids Engineering Summer Meeting, FEDSM 2006, Miami, FL, 17 July 2006 through 20 July 2006 ; Volume 2006 , 2006 ; 0791837831 (ISBN); 9780791837832 (ISBN) ; Firoozabadi, B ; Ghasvari Jahromi, H ; Afshin, H ; Sharif University of Technology
2006
Abstract
Dense underflows are continuous currents, which move down the slope due to the fact that, their density are heavier than ambient water. In turbidity currents the density differences arises from suspended solids. Vicinity of the wall make density currents and wall jets similar in some sense but Variation of density cause this flows more complex than wall jets. An improved form of 'near-wall' k-ε turbulence model is chosen which preserve all characteristics of both density and wall jet currents and a compression is made between them. Then the outcomes from low Reynolds number k-ε model is compared with v2̄-f model which show similarity. Also results show good agreement with experimental data...
The effect of droplet size, channel length and the amount of electromagnetic actuation force on reciprocating movement of mercury droplets in the magneto mercury reciprocating (MMR) micropumps
, Article Sensors and Actuators, A: Physical ; Volume 283 , 2018 , Pages 204-210 ; 09244247 (ISSN) ; Shafii, M. B ; Afshin, H ; Sharif University of Technology
Elsevier B.V
2018
Abstract
Micropumps are regarded as one of the devices used in microsystems, which are responsible for pumping working fluid. The magnetic reciprocating micropump is an example of the existing micropumps in which the pumping agent includes three liquid metal droplets placed inside lateral channels and reciprocated by the electromagnetic force inside their channels. The working fluid located inside the main channel is pumped through due to the movement of these three droplets. The time duration in which the droplet traverses the sub-channel length is crucial in the operation of the suggested micropump. The present study aims to evaluate the effect of the length of sub-channels, moving droplet volume...
Simulation and performance improvement of cryogenic distillation column, using enhanced predictive Peng–Robinson equation of state
, Article Fluid Phase Equilibria ; Volume 489 , 2019 , Pages 117-130 ; 03783812 (ISSN) ; Bayat, M ; Afshin, H ; Sharif University of Technology
Elsevier B.V
2019
Abstract
In this study, a cryogenic distillation column has been designed and simulated via a computer code based on the theta method of convergence. The required thermodynamic properties are determined from the enhanced predictive Peng-Robinson (E-PPR 78) equation of state which has a good accuracy in predicting the corresponding thermodynamic properties of natural gas components. The combined code of distillation column/equation of state has been verified with that of another study. In the present study, the results are achieved by the constant molar over-flow and inclusion of energy equations assumptions. In order to have more accuracy in the results, the energy equations were considered in the...
Investigation of effective parameters on the performance of the helium liquefaction cycle
, Article International Journal of Heat and Technology ; Volume 37, Issue 4 , 2019 , Pages 1009-1018 ; 03928764 (ISSN) ; Eslami, M ; Afshin, H ; Sharif University of Technology
International Information and Engineering Technology Association
2019
Abstract
Due to its unique properties, helium has wide application in different industries and scientific fields, which has turned it into a strategic material. Helium liquefaction plants include wide temperature range from 300 k to 4.2 k, so these plants have high energy consumption. A lot of studies have done to optimize the operation of these cycles. In this research, an exergy analysis is performed for a liquid helium production plant. The optimal performance of 3 and 4 stage cycles is extracted using parametric study and the results are compared with those of Collins dual-expander cycle. The results show that by increasing the number of cooling stages, not only the compressor optimum discharge...
Investigation of effective parameters on the performance of the helium liquefaction cycle
, Article International Journal of Heat and Technology ; Volume 37, Issue 4 , 2019 , Pages 1009-1018 ; 03928764 (ISSN) ; Eslami, M ; Afshin, H ; Sharif University of Technology
International Information and Engineering Technology Association
2019
Abstract
Due to its unique properties, helium has wide application in different industries and scientific fields, which has turned it into a strategic material. Helium liquefaction plants include wide temperature range from 300 k to 4.2 k, so these plants have high energy consumption. A lot of studies have done to optimize the operation of these cycles. In this research, an exergy analysis is performed for a liquid helium production plant. The optimal performance of 3 and 4 stage cycles is extracted using parametric study and the results are compared with those of Collins dual-expander cycle. The results show that by increasing the number of cooling stages, not only the compressor optimum discharge...
Numerical studies on the performance of Saccardo ventilation system in emergency fire scenarios
, Article Applied Mechanics and Materials ; Vol. 527 , 2014 , Pages 146-151 ; ISSN: 16609336 ; Kazemipour, A ; Afshin, H ; Farhanieh, B ; Sharif University of Technology
2014
Abstract
In this study, the influence of volumetric flow rate and inclination angle of air jet is evaluated on the performance of a Saccardo ventilation system in a straight rectangular tunnel in case of fire. Simultaneous effects of volumetric flow rate and inclination angle of jet exiting the Saccardo nozzle on the behavior of smoke plume is considered by studying the structure of velocity profile before the fire source. It is found that this factor has a remarkable influence on the behavior of smoke plume and therefore, on the temperatures experienced near the fire. Besides, the influence of tunnel slope on the performance of the Saccardo system to sweep the plume is investigated. It is shown that...
Theoretical and experimental investigation of density jump on an inclined surface
, Article Scientia Iranica ; Vol. 21, Issue. 5 , 2014 , pp. 1655-1665 ; ISSN :1026-3098 ; Sarnie, M ; Firoozabadi, B ; Afshin, H ; Sharif University of Technology
2014
Abstract
The density jump on an inclined surface is analyzed using an integral method by applying mass and momentum conservation equations. The jump occurs in a two-layered fluid flow in which the upper layer is stagnant and very deep. A relation is derived, which gives the conjugate depth ratio as a function of inlet densimetric Froude number, inlet concentration ratio, bed slope and entrainment. A set of experiments are performed to verify the relation. The theory and the measurements are in good agreement. The analysis reveals that increasing the surface inclination results in a decrease in the conjugate depth ratio. This analysis also shows that the densimetric Froude number just after the jump...
Designing fire scenarios for subway stations and tunnels based on regional approach
, Article Advanced Materials Research, 16 September 2011 through 18 September 2011 ; Volume 433-440 , Septembe , 2012 , Pages 983-991 ; 10226680 (ISSN) ; 9783037853191 (ISBN) ; Maddahin, R ; Afshin, H ; Farhanie, B ; Sharif University of Technology
2012
Abstract
Development of cities as well as population growth causes to development of public transportation especially subway lines. The high capacity besides the high speed in transportation makes them the popular transportation system. Fire is the one of the most important issues that may occur in subways. The difference in flame size, emissionheat, smoke and pollutants generation of subway fires attracts an especial attention of fire investigators. The emergency ventilation of subways in the case of fire should have the ability of discharging heat, smoke and pollutants from passenger escape route and preparing a safe place for a specific duration. The optimal performance of emergency ventilation...
On the motion of Newtonian and non-Newtonian liquid drops
, Article Scientia Iranica ; Volume 19, Issue 5 , 2012 , Pages 1265-1278 ; 10263098 (ISSN) ; Maleki, A ; Firoozabadi, B ; Afshin, H ; Sharif University of Technology
2012
Abstract
In the present study, the motion of Newtonian and non-Newtonian liquid drops has been investigated experimentally. In order to investigate the effect of bulk fluid on drops, we have used water and air, as two fluids with different properties, and various industrial and biological applications. Image processing is utilized to analyze the images obtained by a high speed camera. The research has been separated into two parts. The first part has been devoted to the experiments in which air is the bulk fluid, and the second is related to the experiment carried out in water. The range of Reynolds number is, approximately, 50