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electrohydrodynamics
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Empirical correlation for performance evaluation of electric/corona wind on natural convection
, Article Journal of Electrostatics ; Vol. 72, issue. 1 , February , 2014 , pp. 82-90 ; ISSN: 03043886 ; Shabahang-Nia, E ; Merdasi, A ; Sharif University of Technology
Abstract
The effect of the corona wind on the natural convection at a rectangular channel was investigated experimentally. The results indicate that the natural convection in the absence of electric/corona wind at obtuse angles outperforms than acute angles and keeps improving by increasing the angle. However, the efficiency of the electric/corona wind at acute angles is higher than obtuse angles. Generally, in the presence of electric/corona wind, heat transfer coefficient was increased. The effect of the electric/corona wind was decreased by raising heat flux. This mainly stems from the fact that the temperature gradient raises the thermal boundary layer and reduces the secondary flow power....
Modeling of Micro Combustion Applying Electrohydrodynamics Effects
, M.Sc. Thesis Sharif University of Technology ; Saeedi, Mohammad Hassan (Supervisor) ; Mozafari, Ali Asghar (Supervisor)
Abstract
In this project, one-dimensional and two-dimensional numerical approaches are used to study the effect of applying electrohydrodynamics on the temperature and species mass fraction profiles along the micro-combustor. A premixed mixture of H2-Air with a multi-step chemistry (9 species and 19 reactions) is used and thermal conductivity of the mixture is considered as a function of species thermal conductivity and temperature by using a set of new relations. Both thermal and radical quenching mechanisms are important in the micro-scale combustion due to increasing of area-to-volume ratio and significant heat loss from the combustor walls. By inserting a number of electrodes into the...
Electrohydrodynamically enhanced nucleation phenomenon: A theoretical study
, Article Journal of Enhanced Heat Transfer ; Volume 15, Issue 1 , 2008 , Pages 1-15 ; 10655131 (ISSN) ; Saidi, M. H ; Sharif University of Technology
2008
Abstract
Chaotic behavior of bubbles and their random motion because of the effects of an electric field (EF) motivates statistical approaches for investigating electrohydrodynamically (EHD) enhanced heat transfer. A theoretical model for boiling heat transfer under EHD is presented. The model is based on integral balance of momentum, energy, and interfacial area density, and consists of a system of three coupled equations: conservation of void fraction, bubble number density, and momentum of bubbles. Theoretical results are in qualitative agreement with the available experimental observations in the literature. © 2008 by Begell House, Inc
Fabrication of Micron Resolution Polymer Structures with Electrohydrodynamic Printing
, M.Sc. Thesis Sharif University of Technology ; Movahedi, Mohammad Reza (Supervisor)
Abstract
In recent years, additive manufacturing has been widely used in prototyping and production of industrial-commercial pieces. Additive manufacturing or three-dimensional (3D) printing is able to easily produce any piece for initial prototyping, no matter how complex it is. The fused deposition modeling (FDM) is a type of additive manufacturing process that produces the piece with the mechanism of feeding the PLA filament, then the molten polymer extrusion and depositing the fluid layer by layer with a high viscosity. Since the thickness of the layers is directly proportional to the diameter of the nozzle and the diameter of the used nozzles cannot be in the micron range (lower than 100...
Performance optimization of solar chimney power plant using electric/corona wind
, Article Journal of Electrostatics ; Volume 78 , 2015 , Pages 22-30 ; 03043886 (ISSN) ; Kasaeian, A ; Ghalamchi, M ; Ghalamchi, M ; Sharif University of Technology
Elsevier
2015
Abstract
The effect of the corona wind on the natural convection at absorber of a solar chimney power plant pilot was investigated experimentally. The aim of the study is to improve the efficiency of SCPP through enhanced the heat transfer coefficient of absorber with corona wind. The results show that corona wind enhanced the absorber convective heat transfer coefficient leading to increment in air the velocity and the output power of the SCPP. The amount of heat transfer of pilot increased more than 14.5% when applying voltage of 15 KV and the speed in chimney experienced about 72% amelioration
Colloidal particle reaction and aggregation control in the Electrohydrodynamic 3D printing technology
, Article International Journal of Mechanical Sciences ; Volume 195 , 2021 ; 00207403 (ISSN) ; Movahhedy, M. R ; Khodaygan, S ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
The electrohydrodynamic (EHD) 3D printing technology is an Additive Manufacturing (AM) method that can be used in the manufacture of submicron-size structures. In this process, which is based on the formation of Taylor jet from a metallic ink, the investigation of particles reaction and aggregate formation in ink during printing is of great importance. In this paper, a new Finite Element model based on particle tracing in fluids is presented that couples the different physics that govern an EHD phenomenon. Vortex flow caused by boundary shear stress was observed in the ink jet; which was more like the Marangoni phenomenon in a stationary drop. By experimentally validating the presented model...
Numerical Simulation of Electrospray with Presence of Cone-Jet
,
M.Sc. Thesis
Sharif University of Technology
;
Morad, Mohammad Reza
(Supervisor)
Abstract
In this work, the cone-jet mode of electrospray is simulated by a two phase solver in OpenFoam software. For this aim firstly, breakup of a liquid jet is examined without applying any electric potential to the injecting capillary and results are compared with other works to evaluate the two phase solver. Next with applying electric potential, the whole evolution of cone-jet in time is simulated. One of the most important issues in this mode is the minimum potential that needs to form a stable cone-jet in different flow rates. These minimum voltages are obtained in various flow rates and compared with other experimental and computational works. Result shows that with increasing flow rate the...
An Experimental and Numerical Study on Jet Electrohydrodynamics
, Ph.D. Dissertation Sharif University of Technology ; Morad, Mohammad Reza (Supervisor)
Abstract
Liquid jet behavior in an intense electric field is studied experimentally and numerically.Imaging is used in experiments to charactrize jet behavior. Electrospray of ethanol using a simple needle in a wide range of operating conditions is investigated. Liquid meniscus is captured using a high-speed camera and different electrospray modes are described based on involved forces. A new nozzle is invented that broadens the stability margins of the useful cone-jet mode. The physical mechanisms of the new cone-jet is discussed and it is characterized using appropriate dimensionless parameters. A simple jet in presence of a gaseous crossflow and a normal electric field is also studied. The liquid...
Investigation of Rotational Liquid Film and Electric Power Generation under Electric Field
, M.Sc. Thesis Sharif University of Technology ; Amjadi, Ahmad (Supervisor)
Abstract
Investigation of electrohydrodynamic behavior of fluids under electric fields is a challenging and impressive matter in condensed matter physics. In this thesis, inspired from previous works on liquid film motor, a new phenomenon has been observed and its properties has been investigated.Here by making a new device named “Liquid Film Electric Generator” we produced potential difference on the rotating suspended liquid film under electric field. The power conducted by electrodes has been generated on the surfaces of the film. By this method, under electric field of 1000 V/cm, micro-watt electric power can be achieved on a liquid film of diameter of about 1 cm.We explained this phenomenon on...
Tuning the dispersion of reactive solute by steady and oscillatory electroosmotic-Poiseuille flows in polyelectrolyte-grafted micro/nanotubes
, Article Journal of Fluid Mechanics ; 2019 , Pages 73-112 ; 00221120 (ISSN) ; Saidi, M. H ; Sharif University of Technology
Cambridge University Press
2019
Abstract
This paper extends the analysis of solute dispersion in electrohydrodynamic flows to the case of band broadening in polyelectrolyte-grafted (soft) capillaries by accounting for the effects of ion partitioning, irreversible catalytic reaction and pulsatile flow actuation. In the Debye-Hückel limit, we present the benchmark solutions of electric potential and velocity distribution pertinent to steady and oscillatory mixed electroosmotic-pressure-driven flows in soft capillaries. Afterwards, the mathematical models of band broadening based on the Taylor-Aris theory and generalized dispersion method are presented to investigate the late-time asymptotic state and all-time evolution of...
Tuning the dispersion of reactive solute by steady and oscillatory electroosmotic-Poiseuille flows in polyelectrolyte-grafted micro/nanotubes
, Article Journal of Fluid Mechanics ; 2019 , Pages 73-112 ; 00221120 (ISSN) ; Saidi, M. H ; Sharif University of Technology
Cambridge University Press
2019
Abstract
This paper extends the analysis of solute dispersion in electrohydrodynamic flows to the case of band broadening in polyelectrolyte-grafted (soft) capillaries by accounting for the effects of ion partitioning, irreversible catalytic reaction and pulsatile flow actuation. In the Debye-Hückel limit, we present the benchmark solutions of electric potential and velocity distribution pertinent to steady and oscillatory mixed electroosmotic-pressure-driven flows in soft capillaries. Afterwards, the mathematical models of band broadening based on the Taylor-Aris theory and generalized dispersion method are presented to investigate the late-time asymptotic state and all-time evolution of...
A multiphysics model for analysis of droplet formation in electrohydrodynamic 3D printing process
, Article Journal of Aerosol Science ; Volume 135 , 2019 , Pages 72-85 ; 00218502 (ISSN) ; Movahhedy, M. R ; Khodaygan, S ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
Electrohydrodynamic (EHD) printing is a novel technology used for fabricating high-resolution part features from a wide range of materials. Due to the multiphysics dynamics and the multiphase nature of the microdroplet formation in the EHD printers, modeling of this phenomenon is complicated. In this paper, the formation of a droplet in an EHD printer—under a pulsed electrical field—is simulated using a new numerical model which couples the fluid flow, the electric field distribution and the movement of the electric charges under dynamic and transient conditions. The level-set method is applied to the entire multiphysics domain in order to study the formation of the droplet. The presented...
Electrohydrodynamic Stability of a Cylindrical Jet under an Axial Electric Field
, M.Sc. Thesis Sharif University of Technology ; Kebriaee, Azadeh (Supervisor) ; Morad, Mohammad Reza (Supervisor)
Abstract
Due to the large application of electro-sprays in various industries, the study of the stability of electro-hydrodynamic flows is important. This thesis examines the stability of cylindrical liquid jets in the presence of an axial electric field. The definition of this jet is a simplified model of electrospray, electrospinning. In this model, the stability of a free incompressible cylindrical flow with surface tensile strength, conductivity, polarization, viscosity, and dielectric constant is determined, irrespective of the solubility of the jet and the surrounding fluid (air), in the presence of uniform axial electric field has taken. This will be done by adding the forces generated by the...
System Identification of 3D Electrohydrodynamic Printer for Designing Controller for Controlling Meniscus Height Formated at the Tip of Nozzle
, M.Sc. Thesis Sharif University of Technology ; Movahhedi, Mommad Reza (Supervisor) ; Salarieh, Hassan (Supervisor)
Abstract
3D electrohydrodynamic printer fabricating structure and parts with micron accuracy and resolution is new technology of additional manufacturing. In this method, powerful electric field at the tip of the nozzle can change the shape of the droplet printing and can reduce droplet diameter multiple less than nozzle diameter. Couple equation such as two phase flow, gauss,the effect of various parameter like mechanical and electrical fluid properties, electric field intensity, and folw rate complicate system identification and printer controlling. While the advantages (high speed and resolution, flexibility) of e-jet printing over other fabrication methods are abundant, precise control of the...
Fabrication of Micro-Strain Gauge Using Electrohydrodynamic 3D Printing Technique
, M.Sc. Thesis Sharif University of Technology ; Movahhedy, Mohammad Reza (Supervisor)
Abstract
A significant number of small-scale sensor sales have been reported in recent years. Strain gauges are one of the most common tools for measuring the length change of a part. Nowadays, 3D printing technology can be used in the fabrication of small-scale sensitive sensors, and metal nanoparticles printing are especially suitable for the production of flexible electronic sensors. Electro-hydrodynamic printer, with micro-scale printing capabilities, can be used as a new invention in fabrication of sensors. This type of printer uses the inkjet printing method and the basis of this type of printer is to apply an electric field to shrink the fluid jet. In the present study, pure ethanol was first...
Experimental Investigation of Cooling Hot Surfaces By Electrospray
, M.Sc. Thesis Sharif University of Technology ; Morad, Mohammad Reza (Supervisor)
Abstract
The electrospray technique involves the production of small charged droplets through the application of electrohydrodynamic forces. Under well-defined operating conditions, multiple flow modes can be observed, among which the stable jet-cone mode has received significant attention from the research community. This mode is desirable due to its uniform droplet diameter, reduction in droplet rebound when impacting hot surfaces, and potential for utilizing two-phase heat transfer for cooling purposes. In this study, a comprehensive experimental investigation was conducted to evaluate the cooling of hot surfaces through the use of electrospray in the steady cone-jet mode. The fundamental...
Chain deformation in translocation phenomena
, Article Soft Matter ; Volume 9, Issue 9 , 2013 , Pages 2750-2759 ; 1744683X (ISSN) ; Maleknejad, A ; Varnik, F ; Ejtehadi, M. R ; Sharif University of Technology
2013
Abstract
Deformation of single stranded DNA in a translocation process before reaching the pore is investigated. By solving the Laplace equation in a suitable coordinate system and with appropriate boundary conditions, an approximate solution for the electric field inside and outside a narrow pore is obtained. With an analysis based on the "electrohydrodynamic equivalence" we determine the possibility of the extension of a charged polymer due to the presence of an electric field gradient in the vicinity of the pore entrance. With a multi-scale hybrid simulation (LB-MD), it is shown that an effective deformation before reaching the pore occurs, which facilitates the process of finding the entrance for...
Experimental investigation of the effects of corona wind on the performance of an air-cooled PV/T
, Article Renewable Energy ; Volume 127 , 2018 , Pages 284-297 ; 09601481 (ISSN) ; Kasaeian, A ; Amidpour, M ; Nasirivatan, S ; Mousavi, S ; Sharif University of Technology
Abstract
In the present study, enhancing the heat transfer is experimentally investigated by the electro-hydrodynamics (EHD) through a single-pass air-cooled PV/T (Photovoltaic/Thermal System). The corona wind increases the heat transfer coefficient by producing a secondary flow and vortex, and consequently, increases the PV/T system efficiency. The effects of the corona wind are studied by changing the voltage values and the flow rates in the air channel. The results show that the corona wind is effective on enhancing the system performance; so that the heat transfer coefficient increases by 65% in natural flow regime by applying 11 kV voltage in the pilot setup. Totally, the thermal efficiency of...
Liquid soap film generates electricity: a suspended liquid film rotating in an external electric field as an electric generator
, Article Microfluidics and Nanofluidics ; Vol. 18, issue. 1 , Apr , 2014 , pp. 141-147 ; ISSN:16134982 ; Feiz, M. S ; Namin, R. M ; Sharif University of Technology
Abstract
We have observed that a rotating liquid soap film generates electricity when placed between two non-contact electrodes with a sufficiently large potential difference. In our experiments, suspended liquid film (water + soap film) is formed on the surface of a circular frame, which is forced to rotate in the x−y horizontal plane by a motor. This system is located at the center of two capacitor-like vertical plates to apply an external electric voltage difference in the x-direction. The produced electric current is collected from the liquid film using two conducting electrodes that are separated in the y-direction. We previously reported that a liquid film in an external electric field rotates...
Rotational regimes of freely suspended liquid crystal films under electric current in presence of an external electric field
, Article Microfluidics and Nanofluidics ; Volume 13, Issue 1 , 2012 , Pages 83-89 ; 16134982 (ISSN) ; Amjadi, A ; Ejtehadi, M. R ; Mozaffari, M. R ; Feiz, M. S ; Sharif University of Technology
2012
Abstract
The electrohydrodynamic (EHD) vortices produced by an electric current in freely suspended liquid crystal (LC) films of N-(4-methoxybenzylidene)-4- butylaniline (MBBA), convert to a pure rotation in the presence of external electric field (E ext) perpendicular to the current direction. Here, the direction and strength of the rotation are precisely under control by our self-made device called "liquid-film motor". In this paper, we present experimental observations of the EHD fluid flow when external electric field varies from zero to a value in which pure rotation on the liquid crystal (LC) film is observed. We also show experimentally that the presence of external electric field causes a...