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Experimental Investigation of Effect of Nanofluid Stability on Thermal Performance and Flow Regimes in Pulsating Heat Pipe
, M.Sc. Thesis Sharif University of Technology ; Saeedi, Mohammad Hassan (Supervisor)
Abstract
Pulsating heat pipe (PHP) is a type of wickless heat pipe that has a simple structure and an outstanding thermal performance. Nanofluid is a type of fluifid in which nanoparticles are dispersed in a base fluid and has a better thermal conductivity in comparison with its base fluid. In this article, the performance of a nanofluid PHP is investigated. In order to simultaneously investigate the thermal performance and flow regimes in the PHP, a one-turn copper PHP with a Pyrex glass attached to its adiabatic section was used. A one-turn Pyrex PHP was also used to fully visualize flow patterns in the PHP. Our results showed that the material that a PHP made of and temperature of working fluid...
Effect of vortex generators on hydrodynamic behavior of an underwater axisymmetric hull at high angles of attack
, Article Journal of Visualization ; Volume 20, Issue 3 , 2017 , Pages 559-579 ; 13438875 (ISSN) ; Hejranfar, K ; Farajollahi, A. H ; Sharif University of Technology
Springer Verlag
2017
Abstract
Abstract: Underwater vehicles when yawed to free stream flow, like submarines in a turning maneuver, produce large vortical separated regions. This vortical flow affects acoustic, body drag, control effectiveness and maneuverability. A suitable way to reduce the effects of this separated flow is to use vortex generators. The main goal of this study is to investigate the effect of the vortex generator on the flow field around a standard underwater model employing the vortex generators by using the oil flow visualization method in wind tunnel only in yaw direction (0° ≤ β ≤ 30° angles of attack, due to the experimental cost) and the CFD method in the pitch direction (0° ≤ α ≤ 30° angles of...
Effect of Aquatic Plants on Hydrodynamic and Dispersion in the Wave Motion
, Ph.D. Dissertation Sharif University of Technology ; Jamali, Mirmosadegh (Supervisor)
Abstract
Aquatic plants play an important role in water environment. Increasing drag force, distorting the velocity and turbulence structures and other related parameters, are the results of the presences of plants. These changes affect the dispersion and mass transport in the aquatic areas. This thesis presents laboratory visualizations and measurements of wave motion, and passive solute surface dispersion (longitudinal and lateral) in arrays of cylinders, a model for emergent, rigid aquatic plants. In the range of (where is Keulegan–Carpenter number, is the maximum oscillatory velocity perpendicular to the cylinder axis, is the period of oscillation, and is the diameter of the cylinder), and (where...
Visualization of Flow Pattern and Experimental Investigation of Thermal Performance of Pulsating Heat Pipe with Proposed Fluid
, M.Sc. Thesis Sharif University of Technology ; Saeedi, Mohammad Hassan (Supervisor) ; Shafii, Mohammad Behshad ($item.subfieldsMap.e)
Abstract
Pulsating heat pipe (PHP) is a two-phase device for the means of transferring high heat fluxes and is used extensively for the electronic cooling. In this study the different flow regimes in PHP with different fluids have been investigated. In this research, 3 different fluids including: Pure fluids, Ferro-fluid and surfactant solution with %50 filling ratio have been used. For ferro-fluid, 5 different concentrations and 3 type of magnetic fields have been operated in 2 different heat pipes. Results show that ferrofluid is more stable in Pyrex made-heat pipe for long period of time and no magnet mode has the best thermal performance due to high conductivity of fluid. In copper made-heat pipe...
Experimental Investigation ofClosed-loop Pulsating Heat-pipe with an Additional Branch in the Evaporator Section
, M.Sc. Thesis Sharif University of Technology ; Shafii, Mohammad Behshad (Supervisor)
Abstract
The main idea of this investigation is to increase heat transfer rate by increasing flow circulation of working fluid. By placing additional branches in the evaporator section, secondary bubble pumps were created which improved the circulation of fluid inside PHP. This research was implemented in two distinct phases. In the first phase, the novelty was implemented on a single turn PHP and in the second phase, the same procedure was implemented on a 4-turn PHP. In order to investigate the impact of these additional branches, two similar heat pipes were fabricated. One of them was the conventional PHP and the other had additional branches and is named additional branch PHP (AB-PHP). Thermal...
Performance Improvement of the Flat Plate Pulsating Heat Pipe with Diagonal Grooves
, M.Sc. Thesis Sharif University of Technology ; Shafiee, Mohammad Behshad (Supervisor) ; Moosavi, Ali (Co-Supervisor)
Abstract
The main purpose of this study was to increase the flow circulation within the flat plate oscillating heat pipes as a result Increase the heat transfer rate by placing diagonal grooves in the evaporator. The project in two stages a simple page and diagonal companion page are provided to investigate the effect of diagonal grooves. First a simple plate and then a second one with diagonal grooves in the evaporator it was made. Thermal performance of the heat pipes at each of the stages at different filling ratios of 40%, 50%, 60% and 70% for variable input capacities have been studied and compared. The results of the second stage showed that the performance of the new heat pipe at the optimum...
Experimental Investigation of Crescent-Shaped Jets in Crossflow
, M.Sc. Thesis Sharif University of Technology ; Kebriaee, Azadeh (Supervisor) ; Taiebi Rahni, Mohammad (Co-Supervisor)
Abstract
In this thesis, the physics related to liquid jet injection from injectors with three different crescent-shaped cross-sectional levels into steady and transverse flow were studied. The imaging method in this research was based on shadowgraph, which enables high-speed imaging. With the help of the obtained images, the breakup regimes, including Rayleigh, first and second wind-induced instabilities, were observed for injection into the steady flow. Furthermore, breakup regimes for jet injection into transverse flow, including columnar, columnar-bag, and bag, were also observed. The characteristics of the breakup height in steady flow and the length and height of the breakup along with the jet...
An experimental review on microbubble generation to be used in echo-particle image velocimetry method to determine the pipe flow velocity
, Article Journal of Fluids Engineering, Transactions of the ASME ; Volume 135, Issue 3 , Feb , 2013 , Paper No: FE-12-1217 ; 00982202 (ISSN) ; Shafii, M. B ; Shirani, S ; Sharif University of Technology
2013
Abstract
Microbubbles are broadly used as ultrasound contrast agents. In this paper we use a low-cost flow focusing microchannel fabrication method for preparing microbubble contrast agents by using some surface active agents and a viscosity enhancing material to obtain appropriate microbubbles with desired lifetime and stability for any in vitro infusion for velocity measurement. All the five parameters that govern the bubble size extract and some efforts are done to achieve the smallest bubbles by adding suitable surfactant concentrations. By using these microbubbles for the echo-particle image velocimetry method, we experimentally determine the velocity field of steady state and pulsatile pipe...
Interactive educational tool for teaching a simple cipher
, Article Proceedings - 2014 International Symposium on Biometrics and Security Technologies, ISBAST 2014, 26 August 2014 through 27 August 2014 ; 2015 , Pages 102-105 ; 9781479964444 (ISBN) ; Zahedi, E ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2015
Abstract
In this paper, a practical educational tool based on Java programming is described. The approach is based on using a fully interactive graphical user interface for teaching cipher algorithms. As an example, a transposition cipher is covered, where students can try different keys and observe the effect of parameters such as key length, choice of letters for the key on the ciphertext. At the same time, the process of breaking the cipher algorithm (cryptanalysis) is rendered possible by students injecting known plaintext. The developed program offers an option where it tries systematically all keys (brute force) to break the cipher. Being extendable, the platform is thought to be able to play a...
Spray characteristics and atomization behavior of bio-diesel (Norouzak) and diesel fuel blends
, Article Particulate Science and Technology ; 2016 , Pages 1-12 ; 02726351 (ISSN) ; Jafari, M ; Ahari, M ; Saidi, M. H ; Hajinezhad, A ; Mozaffari, A. A ; Sharif University of Technology
Taylor and Francis Inc
2016
Abstract
Norouzak oil seeds that are the source of bio-diesel (Norouzak) fuel grow mostly in Gonabad and Kashmar located in Khorasan, north east of Iran. Spray characteristics of Norouzak bio-diesel have been experimentally and theoretically studied in this work. Norouzak fuel is added to the conventional diesel fuel, and mixture formations of several blends have been investigated and compared with each other. Moreover, by varying ambient and injection conditions, behaviors of spray of different blends have been explored. Microscopic and macroscopic properties of spray such as Sauter Mean Diameter (SMD), Ohnesorge number, spray tip penetration, spray cone angle, spray projected area and volume have...
Visualization and comparative investigations of pulsating ferro-fluid heat pipe
, Article Applied Thermal Engineering ; Volume 116 , 2017 , Pages 56-65 ; 13594311 (ISSN) ; Saidi, M. H ; Shafii, M. B ; Vandadi, M ; Kalan, K ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
Pulsating heat pipes (PHPs) are among the best solutions for the electronics cooling due to their low cost, effectiveness and being passive. Experiments to study the effective factors on heat transfer performance have been designed and as a result, improvement of ferrofluid PHP performance has been achieved. Two different heat pipes made of copper and glass were prepared to investigate the behavior of magnetic nanofluids. In order to find the best condition for heat transfer performance, different concentrations of nanofluid with a filling ratio of 50% were tested in 3 different cases of magnetic field. The results indicated that the ferrofluid is more stable in the glass PHP. It also shows...
Flow visualization around a non-circular tube
, Article International Journal of Engineering, Transactions B: Applications ; Volume 19, Issue 1 , 2006 , Pages 73-82 ; 1728-144X (ISSN) ; Lavasani, A. M ; Sharif University of Technology
Materials and Energy Research Center
2006
Abstract
The flow behavior around a cam shaped tube in a cross flow has been investigated experimentally using flow visualization and pressure distribution measurements. The range of attack angle and Reynolds number based on an equivalent circular diameter are within 0 < α < 360° and 2×104Reeq <3.4×104, respectively. The pressure drag features are clarified in relation to the flow behavior around the tube. It is found that the highest pressure drag coefficient occurs at α = 90° and 270° over the whole range of Reynolds number. Results show that the pressure drag coefficient of the cam - shaped tube is lower than that of a circular tube with the same surface area for more of the attack angles
Experimental investigation of air-water, two-phase flow regimes in vertical mini pipe
, Article Scientia Iranica ; Volume 18, Issue 4 B , August , 2011 , Pages 923-929 ; 10263098 (ISSN) ; Saidi, M. H ; Nouri Gheimasi, A ; Ghanbarzadeh, S ; Sharif University of Technology
2011
Abstract
In this study, the flow patterns of air-water, two-phase flows have been investigated experimentally in a vertical mini pipe. The flow regimes were observed by a high speed video recorder in pipes with diameters of 2,3 and 4 mm and length 27, 31 and 25 cm, respectively. The comprehensive visualization of air-water, two-phase flow in a vertical mini pipe has been performed to realize the physics of such a two-phase flow. Different flow patterns of air-water flow were observed simultaneously in the mini pipe at different values of air and water flow rates. Consequently, the flow pattern map was proposed for flow in the mini-pipe, in terms of superficial velocities of liquid and gas phases. The...
Dispersion around a circular cylinder in surface wave motion
, Article Scientia Iranica ; Vol. 21, issue. 3 , 2014 , p. 548-556 ; 10263098 ; Jamali, M ; Sharif University of Technology
Abstract
In this paper, we examine fluid flow and associated dispersion around a circular cylinder under progressive surface wave motion. The flow field and vortex shedding patterns were studied using flow visualization and Particle Image Velocimetry (PIV). Several patterns of vortex shedding were identified around a single cylinder. The vortex shedding patterns under progressive wave motion are similar to those observed in planar oscillatory flow, except in the way the vortices form and in the orientation they take. The observed vortex patterns in progressive wave motion are more unstable than those in planar oscillatory flow. Using particle tracking and the Lagrangian dispersion method, the...
Experimental investigation of secondary and tertiary oil recovery from fractured porous media
, Article Journal of Petroleum Exploration and Production Technology ; Volume 3, Issue 3 , September , 2013 , Pages 179-188 ; 21900558 (ISSN) ; Ayatollahi, S ; Rahmanifard, H ; Jahanmiri, A ; Riazi, M ; Sharif University of Technology
2013
Abstract
Naturally fractured reservoirs (NFRs) contribute in large extent to oil and gas production to the ever increasing market demand of fossil energy. It is believed that the vertical displacement of oil during gas injection assisted by gravity drainage (GAGD) is one of the most efficient methods for oil recovery in these reservoirs. Hence, in this work, unconsolidated packed models of cylindrical geometry surrounded by fracture were utilized in order to perform a series of flow visualization experiments during which the contribution of different parameters such as the extent of matrix permeability, physical properties of oil (viscosity, density, and surface tension) and the withdrawal rate was...
Visual technique for detection of gas-liquid two-phase flow regime in the airlift pump
, Article Journal of Petroleum Science and Engineering ; Volume 75, Issue 3-4 , January , 2011 , Pages 327-335 ; 09204105 (ISSN) ; Ghanbarzadeh, S ; Saidi, M. H ; Sharif University of Technology
Abstract
Simplicity of manufacturing and high reliability of airlift pumps have promoted these pumps to be used in different industries, such as petrochemical and oil industries, especially in oil recovery from dead wells. One of the main parameters affecting the performance of these pumps is two-phase flow regime in the main pipe of the pump. In this research, experimental data are utilized to investigate the influence of the flow regimes on the performance of an airlift pump. The data are obtained for air-water two-phase flow in a vertical pipe with a diameter of d = 50. mm and an aspect ratio of L/d = 120. In this study, the gas liquid upward two-phase flow regime in the upriser pipe is...
An experimental study of buzz instability in an axisymmetric supersonic inlet
, Article Scientia Iranica ; Volume 18, Issue 2 B , 2011 , Pages 241-249 ; 10263098 (ISSN) ; Farahani, M ; Asgari Kaji, M. H ; Sharif University of Technology
Abstract
An experimental study was carried out on an axisymmetric supersonic inlet with external compression. The scope of this study was to investigate the general characteristics of the inlet buzz under various design and off-design conditions. The model was equipped with accurate and high frequency pressure sensors and the tests were conducted at Mach numbers varying from 1.8 to 2.5, at various angles of attack, and at different mass flow rates. Shadowgraph flow visualization, together with a high speed camera, was used to capture the external shock structure in front of the inlet. Frequencies of buzz were obtained from both the shadowgraph pictures and analysis of the pressure data. The amplitude...
Experimental investigation of flow instability in a supersonic inlet
, Article ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, ESDA2010, 12 July 2010 through 14 July 2010, Istanbul ; Volume 3 , 2010 , Pages 515-521 ; 9780791849170 (ISBN) ; Farahani, M ; Sharif University of Technology
2010
Abstract
An extensive wind tunnel test series were conducted on an axisymmetric supersonic inlet. The model was tested at Mach numbers from 1.8 to 2.2 and at different values of mass flow rate. Shadowgraph flow visualization was used to capture the external shock structure in front of the inlet. The goal of this study is to find out the general characteristics of the inlet buzz. Frequencies of the buzz have been achieved from the analysis of the pressure data as well as the shadowgraph pictures. The amplitude of the shock waves motion has been measured from the visualization pictures too. In the some large value of mass flow rate, the frequency of shock oscillation increased versus Mach number. Also...
Experimental investigation of spray characteristics of a modified bio-diesel in a direct injection combustion chamber
, Article Experimental Thermal and Fluid Science ; 2016 ; 08941777 (ISSN) ; Saidi, M. H ; Hajinezhad, A ; Mozafari, A. A ; Sharif University of Technology
Elsevier Inc
2016
Abstract
Macroscopic and microscopic characteristics of spray of a Modified Bio-diesel Fuel (MBF), applying direct injection system have been explored and compared with those of conventional diesel fuel. MBF is a new combination of bio-diesel, molasses bio-ethanol, and water, which has been kept as a single-phase bio-fuel, employing an emulsifier. Lower emissions and production costs, higher oxygen content and cetane number are the key advantages of the MBF to be replaced by conventional fossil fuels in internal combustion engines. Applying atomization model, the spray atomization properties such as Ohnesorge number and Sauter Mean Diameter (SMD) have been investigated. Air entrainment analysis has...
Experimental study of flow field on stepped airfoil at very low Reynolds number
, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 231, Issue 9 , 2017 , Pages 1706-1717 ; 09544100 (ISSN) ; Ghassemi, H ; Ebrahimi, A ; Ghasemi, B ; Sharif University of Technology
Abstract
In this article, the flow field around NACA0024 airfoil with step at lower and upper surfaces is experimentally investigated. For this purpose, particle image velocimetry technique based on the instantaneous flow structures is used to investigate the flow field around the airfoil at different times. All the experimental measurements in current study are conducted at very low Reynolds number condition based on the chord of the airfoil (Re=2000) and at angles of attack at 0° and 5° where the flow around airfoils is separated. The differences between vortical structures, mean streamlines, sizes of the wake regions, and vortex shedding of the stepped airfoils compared to unmodified airfoil are...