Ali Dolatabadi

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Swiss Federal Institute of Technology (ETH)

Gareth McKinley

Massachusetts Institute of Technology (MIT)

Tampere University

National Institute of Aerospace

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Papers by Ali Dolatabadi

Engineering surface texture and hierarchical morphology of suspension plasma sprayed TiO 2 coatings to control wetting behavior and superhydrophobic properties

Surface and Coatings Technology, 2017

Engineering surface texture and hierarchical morphology of suspension plasma sprayed TiO2 coating... more

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Flattening of a hollow droplet impacting a solid surface

Journal of Fluid Mechanics

The interaction of a hollow droplet impacting a solid surface occurs in several applications, inc... more The interaction of a hollow droplet impacting a solid surface occurs in several applications, including controllable biomedicine and thermal spray coating. Understanding the physics of the hollow droplet spreading is the key to maintaining the mass transfer process in all relevant applications. In this work, a comprehensive experimental, numerical and theoretical study is performed on water hollow droplets impacting a rigid surface to better understand the flattening process of a hollow droplet. In the numerical part, compressible Navier–Stokes equations are solved using the volume of fluid (VOF) method in a two-dimensional (2-D)-axisymmetric model. The comparison of simulation results with the experimental photographs shows that the numerical solution can correctly predict the hollow droplet shape evolution. The results show that the spreading diameter and height of the counter-jet formed after the hollow droplet impact grow with impact velocity. Investigating the size and location...

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Simulation of Biodiesel Jet in Cross Flow

Liquid jet in cross flow has many applications such as in gas turbine combustion chamber, ramjets... more Liquid jet in cross flow has many applications such as in gas turbine combustion chamber, ramjets, scramjets and agriculture industry. Furthermore, it can be served as a fundamental study of spray quality for different fuels as it illustrates jet disintegration, surface waves, primary and secondary breakups, effect of viscosity, effect of surface tension and the effect of density of the fuel on the final droplet size distribution, mixing, evaporation and combustion processes. In the last decade, scientists and industries have been attracted to the use of renewable energy such as biofuels. Biodiesel as an alternative for diesel, which is already in use by many industries such as transportation and energy, played a pioneer role in this direction. Moreover biodiesel has different renewable resources including Canola oil, cottonseed oil, animal fat, soybean oil, yellow grease and brown grease. Contrary to these advantages, the ignition, atomization and evaporation of biodiesel have been critiqued. In a recent comparative study by the authors, it has been shown experimentally that biodiesel has lower penetration depth comparing to diesel. The lower penetration depth is thought to be as a reason of primary breakup and jet column bending before the disintegration.

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Dispersion of capillary waves in elliptical cylindrical jets

Submitted for the DFD11 Meeting of The American Physical Society Dispersion of capillary waves in... more Submitted for the DFD11 Meeting of The American Physical Society Dispersion of capillary waves in elliptical cylindrical jets GHOBAD AMINI, ALI DOLATABADI, Concordia University-In this work motion of a low speed liquid jet issuing from an elliptic orifice through the air is studied. Mathematical solution of viscous free-surface flow for this asymmetric geometry is simplified by using one-dimensional Cosserat (directed curve) equations which can be assumed as a low order form of Navier-Stokes equations for slender jets. Linear solution is performed and temporal and spatial dispersion equations are derived. Growth rate and phase speed of unstable and stable modes under various conditions are presented. The possibility of instability of asymmetric disturbances is studied too. With distance down the jet, major and minor axes are altered and finally jet breaks up due to capillary instability. The effect of jet velocity and viscosity and also orifice ellipticity on axis-switching and breakup is investigated.

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On the modeling of viscoelastic droplet impact dynamics

In this paper, a numerical modeling of the impact, spreading, and eventually rebound of a viscoel... more In this paper, a numerical modeling of the impact, spreading, and eventually rebound of a viscoelastic droplet is reported. The numerical model is based on the volume of fluid (VOF) method coupled with the FENE-CR constitutive equations, and accounts for both the surface tension and the substrate wettability. The FENE-CR constitutive equations are used to model the polymer solution, while taking advantage of its rheological characterization. The comparison is performed between droplets of Newtonian solvent and a monodisperse polymer solution. The droplet impact on both hydrophilic and superhydrophobic substrate is analyzed through a detailed analysis of the spreading diameter evolution. It is found that while the droplet kinematic phase seems independent of the substrate and fluids properties, the recoiling phase is highly related to all of them. In addition the model infers a critical polymer concentration above which the droplet rebound from a superhydrophobic substrate is suppressed. The simulation is of particular interest to ink-jet processing, and demonstrates the capability of the model to handle complex non-Newtonian droplet dynamics.

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A three-dimensional numerical study of the breakup length of liquid sheets

Concurrent Droplet Coalescence and Solidification on Surfaces With Various Wettabilities

Journal of Fluids Engineering, 2015

An experimental study is performed to analyze the shear driven droplet shedding on cold substrate... more An experimental study is performed to analyze the shear driven droplet shedding on cold substrates with different airflow speeds typical of those in the flight conditions. Understanding the mechanism of simultaneous droplet shedding, coalescence, and solidification is crucial to devise solutions for mitigating aircraft in-flight icing. To mimic this scenario, the experimental setup is designed to generate shear flow as high as 90 m/s. The droplet shedding at high-speed is investigated on a cold surface (0 and −5 °C) of different wettabilities ranging from hydrophilic to superhydrophobic. Result analyses indicate that on a hydrophilic substrate, the droplets form a rivulet, which then freezes on the cold plate. In contrast, on the superhydrophobic surface, there is no rivulet formation. Instead, droplets roll over the substrate and detach from it under the effect of high shear flow.

Instability of elliptic liquid jets: Temporal linear stability theory and experimental analysis

Physics of Fluids, 2014

The instability dynamics of inviscid liquid jets issuing from elliptical orifices is studied, and... more The instability dynamics of inviscid liquid jets issuing from elliptical orifices is studied, and effects of the surrounding gas and the liquid surface tension on the stability behavior are investigated. A dispersion relation for the zeroth azimuthal (axisymmetric) instability mode is derived. Consistency of the analysis is confirmed by demonstrating that these equations reduce to the well-known dispersion equations for the limiting cases of round and planar jets. It is shown that the effect of the ellipticity is to increase the growth rate over a large range of wavenumbers in comparison to those of a circular jet. For higher Weber numbers, at which capillary forces have a stabilizing effect, the growth rate decreases with increasing ellipticity. Similar to circular and planar jets, increasing the density ratio between gas and liquid increases the growth of disturbances significantly. These theoretical investigations are complemented by experiments to validate the local linear stability results. Comparisons of predicted growth rates with measurements over a range of jet ellipticities confirm that the theoretical model provides a quantitatively accurate description of the instability dynamics in the Rayleigh and first wind-induced regimes.

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Effect of gravity on capillary instability of liquid jets

Physical Review E, 2013

The effect of gravity on the onset and growth rate of capillary instabilities in viscous liquid j... more The effect of gravity on the onset and growth rate of capillary instabilities in viscous liquid jets is studied. To this end, a spatial linear stability analysis of Cosserat's equations is performed using a multiscale expansion technique. A dispersion relation and expressions for the perturbation amplitude are derived to evaluate the growth rate of the most-unstable axisymmetric disturbance mode. Modeling results are compared with classical results in the limit of zero Bond number, confirming the validity of this approach. Expressions for the critical Weber number, demarcating the transition between convective and absolute instability are derived as function of capillary and Bond numbers. Parametric investigations for a range of relevant operating conditions (characterized by Capillary, Weber, and Bond numbers) are performed to examine the jet breakup and the perturbation growth-rate. In addition to the physical insight that is obtained from this investigation, the results that are presented in this work could also be of relevance as test-cases for the algorithmic development and the verification of high-fidelity multiphase simulation codes.

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Phase Formation and Transformation in Alumina/YSZ Nanocomposite Coating Deposited by Suspension Plasma Spray Process

Journal of Thermal Spray Technology, 2010

Suspension Plasma Spray process was used for deposition of pseudo-eutectic composition of alumina... more Suspension Plasma Spray process was used for deposition of pseudo-eutectic composition of aluminayttria-stabilized zirconia as a potential thermal barrier coating using Mettech axial III torch. Process variables including feed and plasma parameters were altered to find their effects on the formation of phases in the composite coating. The in-flight particle velocity was found to be the crucial parameter on phase formation in the resulting coatings. Low particle velocities below 650 m/s result in the formation of stable phases i.e., a-alumina and tetragonal zirconia. In contrast, high particle velocities more than 750 m/s favor the metastable c-alumina and cubic zirconia phases as dominant structures in as-deposited coatings. Accordingly, the plasma auxiliary gas and plasma power as influential parameters on the particle velocity were found to be reliable tools in controlling the resulting coating structure thus, the consequent properties. The noncrystalline portion of the coatings was also studied. It was revealed that upon heating, the amorphous phase prefers to crystallize into pre-existing crystalline phases in the as-deposited coating. Thus, the ultimate crystalline structure can be designed using the parameters that control the particle velocity during plasma spray coating.

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Characterization and modeling of 2D-glass micro-machining by spark-assisted chemical engraving (SACE) with constant velocity

Journal of Micromechanics and Microengineering, 2008

Spark-assisted chemical engraving (SACE) is an unconventional micro-machining technology based on... more Spark-assisted chemical engraving (SACE) is an unconventional micro-machining technology based on electrochemical discharge used for micro-machining nonconductive materials. SACE 2D micro-machining with constant speed was used to machine micro-channels in glass. Parameters affecting the quality and geometry of the micro-channels machined by SACE technology with constant velocity were presented and the effect of each of the parameters was assessed. The effect of chemical etching on the geometry of micro-channels under different machining conditions has been studied, and a model is proposed for characterization of the micro-channels as a function of machining voltage and applied speed.

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High-Temperature Performance of Alumina-Zirconia Composite Coatings Containing Amorphous Phases

Advanced Functional Materials, 2011

presents high thermal stability even at temperatures as high as 1500 ° C.

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Bouncing of cloud-sized microdroplets on superhydrophobic surfaces

Physics of Fluids, 2020

Numerical investigation of surface curvature effect on the self-propelled capability of coalesced... more

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Anti-icing performance and durability of suspension plasma sprayed TiO2 coatings

Cold Regions Science and Technology, 2018

, Anti-icing performance and durability of suspension plasma sprayed TiO2 coatings4. Coltec (2018),

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Instability of Elliptic Liquid Jets

Journal of Fluid Mechanics

INSTABILITY OF ELLIPTIC LIQUID JETS GHOBAD AMINI-BAZIANI The motion of liquid jets ejected from e... more INSTABILITY OF ELLIPTIC LIQUID JETS GHOBAD AMINI-BAZIANI The motion of liquid jets ejected from elliptical orifices is studied theoretically and experimentally. In the theoretical part of the study, the linear evolution of initially small disturbances on the inviscid jets is investigated using a three-dimensional analysis. In addition, to study the viscous free-surface flows, an approach based on the Cosserat theory (also called directed theory) is used. Temporal and spatial analyses are performed and the dispersion equations of waves on the jet column are derived to show the growth rate of disturbances for different modes under various conditions. An equation for the jet profile is suggested which describes the axis-switching phenomenon and breakup for various conditions. The equations are approximated for small and large ellipticities, and wellknown dispersion relations of circular and planar jets are retrieved. It is shown that in the xvi "The history of science teaches only too plainly the lesson that no single method is absolutely to be relied upon, that sources of error lurk where they are least expected, and that they may escape the notice of the most experienced and conscientious worker."

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Formation of Solid Solution and Metallic Nickel Phases During Suspension Plasma Spraying of Co Oxide and Ni Oxide

Thermal Spray 2021: Proceedings from the International Thermal Spray Conference, 2021

The focus of this study is the formation of a solid solution and metallic nickel in the cobalt-ni... more The focus of this study is the formation of a solid solution and metallic nickel in the cobalt-nickel mixed oxide coatings during suspension plasma spray (SPS) deposition. The (Co,Ni)O solid solution is a potential material for inert anode applications in aluminum production. SPS coatings and in-flight collected particles are studied to gain further insight into the melting and mixing phenomena of the NiO and CoO powders as well as phase formation in the deposited coatings. Moreover, the role of suspension feedstock particle sizes on the microstructure of coatings is discussed. SEM, EDS and X-ray diffraction studies helped better understanding the formation of different crystalline phases within the as-sprayed coatings. It was found that the formation of metallic nickel is possible in the coatings. The results support the importance of substrate temperature on the formation of metallic Ni, so that keeping the substrate at low temperature results in an increase of the Ni content in t...

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Formation of Solid Solution and Metallic Nickel Phases During Suspension Plasma Spraying of Co Oxide and Ni Oxide

Thermal Spray 2021: Proceedings from the International Thermal Spray Conference, 2021

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Effect of Electrode Shape on Droplet Actuation in Electrowetting-Based Microfluidics

Volume 13: Nano-Manufacturing Technology; and Micro and Nano Systems, Parts A and B, 2008

This article describes the effect of electrode shape in electrowetting-based droplet actuation. A... more This article describes the effect of electrode shape in electrowetting-based droplet actuation. A Volume of Fluid technique is applied to track the 3-D interface. The Laplace equation is solved to predict the time and space dependent electric field in the domain. The onset of actuation, contact angle distribution at the three phase line, and the droplet morphology are studied for two electrode shapes; i.e. flat and crescent. The acceleration and the velocity of the droplet are also other important parameters to show the superior performance of crescent electrode in droplet actuation.

A new design for coating thin film alumina on stainless steel for biomedical applications

Proceedings International Conference on MEMS, NANO and Smart Systems, 2003

Biocompatibility is one of the essential characteristics of implants used in biomedical and denta... more Biocompatibility is one of the essential characteristics of implants used in biomedical and dental applications. The biocompatibility may be affected by many factors, one of which and the most important one, is its corrosion resistance in highly aggressive body fluid. Corrosion of implants causes products of corrosion to accumulate in adjacent tissues and stimulate allergy in patients. Surface modification of

Enhancement of amorphous phase formation in alumina–YSZ coatings deposited by suspension plasma spray process

Surface and Coatings Technology, 2013

In the present work on pseudo-eutectic alumina-yttria stabilized zirconia (YSZ) composite, the in... more In the present work on pseudo-eutectic alumina-yttria stabilized zirconia (YSZ) composite, the influence of spray parameters on amorphous phase formation during suspension plasma spray deposition is investigated. Several variables were evaluated as the most probable key factors influencing the amorphous phase formation. These variables include powder feed size, in-flight particle characteristics (temperature and velocity), spraying robot travel speed, preheating the substrate, number of deposition passes and the presence of bond coat. It was found that larger particle size, higher robot speed and substrate preheating lead to larger amounts of amorphous phase. Moreover, it is shown that particle velocity and temperature need to be reasonably low to get greater amorphous content while the presence of a bond coat has no significant influence on the amorphous phase formation. In contrast, increasing the number of deposition passes is detrimental to this phase. This work also discusses some correlations observed between the amorphous phase content and the in-flight particle characteristics and coating grain sizes.

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Engineering surface texture and hierarchical morphology of suspension plasma sprayed TiO 2 coatings to control wetting behavior and superhydrophobic properties

Surface and Coatings Technology, 2017

Engineering surface texture and hierarchical morphology of suspension plasma sprayed TiO2 coating... more

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Flattening of a hollow droplet impacting a solid surface

Journal of Fluid Mechanics

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Simulation of Biodiesel Jet in Cross Flow

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Dispersion of capillary waves in elliptical cylindrical jets

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