Search for: recirculations
Total 28 records
Numerical investigation of different geometrical parameters of perforated conical rings on flow structure and heat transfer in heat exchangers, Article Applied Thermal Engineering ; Volume 156 , 2019 , Pages 494-505 ; 13594311 (ISSN) ; Esfahani, J. A ; Sharif University of Technology
Elsevier Ltd 2019
A numerical study has been performed to investigate the flow and heat transfer characteristics of fluid flow through heat exchanger tubes fitted with perforated conical rings. The holes are circular, and the number of holes N is ranged from 0 to 10. The influences of perforated conical ring diameter ratios D2/D1=0.4,0.5and0.6 and the hole diameter ratios d/D=0.06,0.1and0.14 on average Nusselt number, friction factor and thermal performance factor are reported. This analysis is performed in the turbulent flow regime 4000⩽Re⩽14,000 and the governing equations are solved by using (RNG) k-∊ model. Due to strong turbulent intensity, perforated conical rings lead to more flow perturbation and...
Effects of inlet position and baffle configuration on the hydraulic performance of primary settling tanks, Article 2005 ASME International Mechanical Engineering Congress and Exposition, IMECE 2005, Orlando, FL, 5 November 2005 through 11 November 2005 ; Volume 261 FED , 2005 , Pages 613-618 ; 08888116 (ISSN); 0791842193 (ISBN); 9780791842195 (ISBN) ; Tamayol, A ; Ahmadi, G ; ASME Fluids Engineering Division ; Sharif University of Technology
Circulation regions always exist in the settling tanks. These regions reduce the tank's performance and decrease effective volume of the tank. Recirculation zones would also result in short-circuiting and high flow mixing problems. Inlet position would also have effect on these, too. Using good baffle configuration may increase performance of settling tanks. One method for comparison of different tanks with each others is to use FTC. In this paper, by using FTC the effects of inlet position and baffle configuration on the hydraulic performance of primary settling tanks are studied. The best position of baffle is also determined. Copyright © 2005 by ASME
Availability analysis on combustion of n-heptane and isooctane blends in a reactivity controlled compression ignition engine, Article Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering ; Volume 232, Issue 11 , 2018 , Pages 1501-1515 ; 09544070 (ISSN) ; Reyhanian, M ; Ghofrani, I ; Aziz, A. A ; Hosseini, V ; Sharif University of Technology
SAGE Publications Ltd 2018
Unfortunately, energy demands and destruction of the environment from uncontrolled manipulation of fossil fuels have increased. Climate change concerns have resulted in the rapid use of new, alternative combustion technologies. In this study, reactivity controlled compression ignition (RCCI) combustion, which can simply be exploited in internal combustion (IC) engines, is investigated. To introduce and identify extra insightful information, an exergy-based study was conducted to classify various irreversibility and loss sources. Multidimensional models were combined with the primary kinetics mechanism to investigate RCCI combustion, incorporating the second law of thermodynamics. The...
Experimental Investigation of Cold-flow Characteristics in Near-Wake of V-gutter Flameholders
Sharif University of Technology
Morad, Mohammad Reza
Bluff bodies are commonly used to stabilize flames in many high-speed flow applications. V-gutters are one of the most common bluff bodies that are mainly used in ramjet combustors and turbojet or turbofan afterburners for flameholding. Aerodynamic characteristics of flow behind V-gutter has crucial effect on mechanism of flame stabilization, therefore more experimental investigations still seem to be necessary in this area. Particle Image Velocimetry technique which has high temporal and spatial resolution has been used in this research in order to better investigate the structure and dynamics of this unsteady and complex flow filed. Experiments were done on a reference V-gutter in...
Numerical Analyses of Gas Recirculation Effects in Flameless Combustion, M.Sc. Thesis Sharif University of Technology ; Farshchi, Mohammad
Flameless combustion in combustion technology is an innovative method with low nox production that few years provided it passes. In this paper the effects of various parameters on flameless combustion chamber with separate fuel and air jets, has been modeled numerically with the help of Fluent 6.3 software. Differences between traditional combustion and flameless combustion were determined and the flame structure has been studied in different scenarios. In numerical modeling, approach were used to modeling turbulence and eddy dissipation concept (EDC) approach use to modeling combustion and turbulence interaction effects. A global Two-step reaction mechanism for propane and a global...
Investigation of EDC Turbulent Combustion Model for Flameless Combustion Regime in a Certain Combustion Chamber, M.Sc. Thesis Sharif University of Technology ; Farshchi, Mohammad
Reducing carbon emissions emanated from combustion of fossil fuels is a challenging problem and consumes huge amount of money that is put into research every year. Nitrogen oxides are among the most important pollutants which have been at the center of attention of industries and international environment protection organizations, especially due to their increased production by commercial aircrafts at higher altitudes of the atmosphere. Flameless is a combustion regime that has been independently discovered by different research teams while working on reducing nitrogen oxides from burning fossil fuels in the early 1990s, and afterwards has been studied for its exclusive characteristics in...
Using fully implicit conservative statements to close open boundaries passing through recirculations, Article International Journal for Numerical Methods in Fluids ; Volume 53, Issue 3 , 2007 , Pages 371-389 ; 02712091 (ISSN) ; Vakilipour, S ; Sharif University of Technology
The numerical solution of the fluid flow governing equations requires the implementation of certain boundary conditions at suitable places to make the problem well-posed. Most of numerical strategies exhibit weak performance and obtain inaccurate solutions if the solution domain boundaries are not placed at adequate locations. Unfortunately, many practical fluid flow problems pose difficulty at their boundaries because the required information for solving the PDE's is not available there. On the other hand, large solution domains with known boundary conditions normally need a higher number of mesh nodes, which can increase the computational cost. Such difficulties have motivated the CFD...
Prediction of hydraulic efficiency of primary rectangular settling tanks using the non-linear k - ε turbulence model, Article Scientia Iranica ; Volume 17, Issue 3 B , 2010 , Pages 167-178 ; 10263098 (ISSN) ; Ashjari, M. A ; Sharif University of Technology
Circulation is created in some parts of settling tanks. It can increase the mixing level, decrease the effective settling, and create a short circuiting from the inlet to the outlet. All above-mentioned phenomena act in such a way to decrease the tank's hydraulic efficiency, which quantitatively shows how flow within the tank is uniform and quiet. So, the main objective of the tank design process is to avoid forming the circulation zone, which is known as the dead zone. Prediction of the flow field and size of the recirculation zone is the first step in the design of settling tanks. In the present paper, the non-linear k - ε turbulence model is used for predicting the length of the...
Triethylamine removal using biotrickling filter (BTF): effect of height and recirculation liquid rate on BTFs performance, Article International Journal of Environmental Science and Technology ; Volume 14, Issue 8 , 2017 , Pages 1615-1624 ; 17351472 (ISSN) ; Sotoudeheian, S ; Bayat, R ; Sharif University of Technology
Center for Environmental and Energy Research and Studies 2017
This study investigated the removal of triethylamine using a biotrickling filter. The influence of affecting parameters, such as height and recirculation liquid rate (VL) on contaminant removal efficiency, was examined in detail. The results demonstrated that in the constant empty bed residence time (EBRT), when VL was increased, the removal efficiency (RE) increased. Also, for a specific VL, increasing EBRT could also increase RE values. However, it seems that an increasing VL is a more cost-effective way to enhance RE as compared to an increasing EBRT. The obtained outcomes represented that for a constant EBRT, an increase in inlet loading (IL) could decrease RE. For lower ILs, the removal...
Retrofitting a steam power cycle by using water from the interstage feed water pump as reheat spray, Article ASME Power Conference 2008, Lake Buena Vista, FL, 22 July 2008 through 24 July 2008 ; July , 2008 , Pages 23-30 ; 9780791848326 (ISBN) ; Irani Rahaghi, A ; Mousavi, M. S ; Power Division, ASME ; Sharif University of Technology
Various methods are used in thermal power plants to adjust the superheated or reheated steam temperature to a pre-determined set point, including flue gas recirculation, using tilting burners and spray of water from discharge of feed water pump, etc. In this paper, an innovative method is presented to control the reheater temperature by tapping water from an interstage of the feed water pump to control reheater temperature at the Bisotoun Power Plant (a steam cycle based power plant in the western Iran). The spray water for the superheaters is secured from the discharge of feed water pump, but interstage water, instead of gas recirculation or using tilting burner, is used to control the...
Energy and Exergy Analysis of a Turbocharged Three-Cylinder Spark Ignition Engine and the Use of a Vortex Tube to Recover the Exhaust, M.Sc. Thesis Sharif University of Technology ; Kazemzadeh Hanani, Siamak ; Chitsaz, Eiman
In this research energy and exergy Balance has been studied for a turbocharged three-cylinder engine. Energy balance is a method based on the first law of thermodynamics and based on this method the control volume is selected on the engine and the input and output energies of the control volume are calculated. Exergy balance is also a method based on the second law of thermodynamics which achieves the amount of irreversibility and ability to convert useful work for different energies in the control volume. In the tests performed, the net output power, output exhaust energy, energy transferred to the cooling fluid and other energies, including convection and radiation heat transfer from the...
Introducing an adaptive robust controller for artificial heart, Article Proceedings of the IEEE RAS and EMBS International Conference on Biomedical Robotics and Biomechatronics, 24 June 2012 through 27 June 2012 ; June , 2012 , Pages 413-418 ; 21551774 (ISSN) ; 9781457711992 (ISBN) ; Jahed, M ; Sharif University of Technology
Prolonged and uncontrolled high shear stresses and turbulence can cause hemolysis, while alternating and low-level stresses may contribute to platelet activation and thrombus formation. Such deficiencies are reported for Total Artificial Heart (TAH) systems which are generally not fully capable of dynamic adaptation to sudden pressure and volume changes. This study introduces an adaptive robust controller for a linear motor based TAH (LMTAH) which overcomes such shortcomings. Proposed controller performance is compared with simulated natural heart in normal and stressed physiological conditions. Application of adaptive robust control results in flows with less stress variation and...
Experimental investigation of baffle effect on the flow in a rectangular primary sedimentation tank, Article Scientia Iranica ; Volume 17, Issue 4 B , 2010 , Pages 241-252 ; 10263098 (ISSN) ; Firoozabadi, B ; Sharif University of Technology
In primary sedimentation tanks, short-circuiting enlargement of dead zones and high flow mixing problems are caused by circulation regions (dead zones), which can reduce the optimal sedimentation of particles. For proper design of such tanks, the formation of recirculation zones should be avoided. The provision of a baffle as a geometrical modification of a tank may influence the flow field for better sedimentation. Thus, in this study, velocity measurements were performed by a three-dimensional Acoustic Doppler Velocimeter (ADV) to investigate baffle effects on the velocity distribution in a primary rectangular sedimentation tank, quantitatively. Effects of baffle positioning were also...
Large eddy simulation of low swirl flames under external flow excitations, Article Flow, Turbulence and Combustion ; Volume 100, Issue 1 , 2018 , Pages 249-269 ; 13866184 (ISSN) ; Farshchi, M ; Sharif University of Technology
Springer Netherlands 2018
Low swirl flame characteristics under external flow excitations are numerically investigated using large eddy simulations with a dynamically thickened flame combustion model. A finite volume scheme on a Cartesian grid with a dynamic one equation eddy viscosity subgrid scale model is used for large eddy simulations. The excitations are imposed on inlet velocity profiles by a sinusoidal forcing function over a wide range of amplitudes and frequencies. Present investigation shows that although, the swirling motion of the low swirl flame is not intense enough to induce a recirculation zone in ensemble averaged results, external flow excitations increase the local swirl number upstream of the...
Low swirl premixed methane-air flame dynamics under acoustic excitations, Article Physics of Fluids ; Volume 31, Issue 9 , 2019 ; 10706631 (ISSN) ; Farshchi, M ; Chakravarthy, S. R ; Chakraborty, A ; Aravind, I. B ; Wang, B ; Sharif University of Technology
American Institute of Physics Inc 2019
In this study, simultaneous particle image velocimetry and planar laser induced fluorescence of hydroxyl radical, chemiluminescence imaging, and hot-wire measurements are utilized to study reacting low swirl flow dynamics under low to high amplitude acoustic excitations. Results show that a temporal weak recirculation zone exists downstream of the flame, which is enlarged in size under acoustic excitations. Investigations show that temporal behaviors of this recirculation zone play a significant role in flame movements and instabilities. As the acoustic wave amplitude increases, the flame lift-off distance changes drastically, resulting in flame instabilities (flashback and blowout) during...
Heat transfer enhancement of ferrofluid flow within a wavy channel by applying a non-uniform magnetic field, Article Journal of Thermal Analysis and Calorimetry ; Volume 139, Issue 5 , 2020 , Pages 3331-3343 ; Biglarian, M ; Rabienataj Darzi, A. A ; Farhadi, M ; Hassanzadeh Afrouzi, H ; Toghraie, D ; Sharif University of Technology
Springer Netherlands 2020
This paper presents the effects of a non-uniform magnetic field on the hydrodynamic and thermal behavior of ferrofluid flow in a wavy channel by 3D numerical simulation. The wavy surfaces at the top and bottom of the channel are heated by constant heat fluxes. Moreover, the sidewalls are adiabatic. In the wavy section, in the perpendicular direction of the main flow, the magnetic field that linearly varies along the direction of the main flow is applied. The mathematical model that is consistent with the principles of ferrohydrodynamics and magnetohydrodynamics is used for the problem formulation. The results indicate that the wavy wall enhances the heat transfer rate on the bottom of the...
Effect of empty bed residence time on biotrickling filter performance: Case study-triethylamine, Article International Journal of Environmental Science and Technology ; Vol. 11, issue. 1 , 2014 , pp. 183-190 ; ISSN: 17351472 ; Bayat, R ; Keshavarzi Shirazi, H ; Sotoudeheian, S ; Sharif University of Technology
In this study, a laboratory-scale biotrickling filter (BTF) is used to remove Triethylamine (TEA) from gaseous wastes. The BTF is made of stainless steel with a height of 210 cm and an internal diameter of 21 cm packed with lava rocks. TEA elimination pattern was evaluated by changing empty bed residence times (EBRTs). The maximum elimination capacity (EC) has been determined to be 87 g/m3/h. At all EBRTs 52, 31, 20, and 10 s, contaminant transferring from gas phase to liquid was more than the EC. Also, the removal efficiency was 100 % for a mass loading of 100 g/m3/h. While the liquid recirculation velocity of 3.466 m3/m2/h was maintained, the flow rate was adjusted to 60, 100, 156, and 312...
Flow field around single and tandem piers, Article Flow, Turbulence and Combustion ; Volume 90, Issue 3 , April , 2013 , Pages 471-490 ; 13866184 (ISSN) ; Aslani-Kordkandi, A ; Sharif University of Technology
The present study provides a comparison between the flow pattern around two circular piers in tandem and a single pier set up on a moderately rough flat bed in a laboratory flume. Velocities are measured by an Acoustic Doppler Velocimeter (ADV). The contours of the time-averaged velocity components, Reynolds shear stresses, turbulence intensities and turbulence kinetic energy at different planes are presented. Streamlines and vectors are used to study the flow features. The analysis of power spectra around the piers is also presented. The results show that the presence of downstream pier changes the flow structure to a great extent, particularly in the near-wake region. Within the gap...
Data center power reduction by heuristic variation-aware server placement and chassis consolidation, Article CADS 2012 - 16th CSI International Symposium on Computer Architecture and Digital Systems ; 2012 , Pages 150-155 ; 9781467314824 (ISBN) ; Momtazpour, M ; Goudarzi, M ; Sharif University of Technology
The growth in number of data centers and its power consumption costs in recent years, along with ever increasing process variation in nanometer technologies emphasizes the need to incorporate variation-aware power reduction strategies in early design stages. Moreover, since the power characteristics of identically manufactured servers vary in the presence of process variation, their position in the data center should be optimally determined. In this paper, we introduce two heuristic variation-aware server placement algorithm based on power characteristic of servers and heat recirculation model of data center. In the next step, we utilize an Integer Linear Programming (ILP) based...
Numerical simulation of laminar and turbulent two-phase flow in pressure-swirl atomizers, Article AIAA Journal ; Volume 50, Issue 10 , 2012 , Pages 2091-2101 ; 00011452 (ISSN) ; Kebriaee, A ; Sharif University of Technology
This paper has developed an axisymmetric laminar and turbulent two-phase flow solver to simulate pressure-swirl atomizers. Equations include the explicit algebraic Reynolds stress model, the Reynolds-averaged Navier-Stokes, and the level set equation. Applying a high-order compact upwind finite difference scheme with the level set equation being culminated to capture the interface between air-liquid two-phase flow and decreasing the mass conservation error in the level set equation. The results show that some recirculation zones are observed close to the wall in the swirl chamber and to the axis. This model can predict converting the Rankin vortex in the swirl chamber to the forced vortex in...