Tuan Tran

Tuan Tran
Nanyang Technological University | ntu · School of Mechanical and Aerospace Engineering (MAE)

PhD

About

76
Publications
30,244
Reads
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2,180
Citations
Additional affiliations
July 2013 - present
Nanyang Technological University
Position
  • Professor (Associate)
August 2010 - July 2013
University of Twente
Position
  • PostDoc Position
Education
June 2004 - August 2010
University of Illinois, Urbana-Champaign
Field of study
  • Theoretical & Applied Mechanics
August 2000 - June 2004
VNU University of Science
Field of study
  • Engineering Mechanics

Publications

Publications (76)
Article
A liquid drop resting on a soft solid deforms the surface at the three-phase contact line. The surface deformation, also called "wetting ridge", varies in size from nanoscales to microscales, depending on the elasticity and thickness of the soft layer. In this work, we probe how surface elasticity and coating thickness influences normal and tangent...
Article
This study presents a sharp-interface algebraic volume-of-fluid (SA-VOF) approach towards direct numerical simulation of evaporating droplets in a finite-volume framework. An interface identification scheme is introduced to determine a sharp layer of interface cells where liquid-vapor phase change occurs. The rate of vaporization is directly comput...
Preprint
Full-text available
Viscous droplets impinging on soft substrates may exhibit several distinct behaviours including repeated bouncing, wetting, and hovering, i.e., spreading and retracting after impact without bouncing back or wetting. We experimentally study the conditions enabling these characteristic behaviours by systematically varying the substrate elasticity, im...
Article
Viscous droplets impinging on soft substrates may exhibit several distinct behaviours including repeated bouncing, wetting, and hovering, i.e., spreading and retracting after impact without bouncing back or wetting. We experimentally study the conditions enabling these characteristic behaviours by systematically varying substrate elasticity, impact...
Article
Full-text available
During the impact of a liquid droplet on a sufficiently heated surface, bubble nucleation reduces the contact area between the liquid and the solid surface. Using high-speed imaging combined with total internal reflection, we measure and report how the contact area decreases with time for a wide range of surface temperatures and impact velocities....
Article
Electrowetting on dielectric (EWOD) is a powerful tool in many droplet-manipulation applications with a notorious weakness caused by contact-angle saturation (CAS), a phenomenon limiting the equilibrium contact angle of an EWOD-actuated droplet at high applied voltage. In this paper, we study the spreading behaviours of droplets on EWOD substrates...
Article
Electronic devices with high power density require efficient and compact heat transfer management methods. While passive fins have been routinely used for heat dissipation, they usually have a limited range of operating conditions in electronic applications. In this study, we explore experimentally and numerically active enhancement of convective h...
Article
Full-text available
A stone thrown in a lake captures air as it collides with water and sinks; likewise a rain drop falling on a flat surface traps air bubbles underneath and creates a spectacular splash. These natural occurrences, from bubble entrapment to liquid ejection, happen as air fails to escape from the closing gap between liquid and solid surfaces. Trapping...
Book
3D printed electronics have captured much attention in recent years, owing to their success in allowing on-demand fabrication of highly-customisable electronics on a wide variety of substrates and conformal surfaces. This textbook helps readers understand and gain valuable insights into 3D printed electronics. It does not require readers to have an...
Article
Full-text available
Soft surfaces impacted by liquid droplets trap more air underneath than their rigid counterparts. The extended lifetime of the air film not only facilitates bouncing behaviours of the impacting droplets but also increases the possibility of interactions between the air film itself and the air cavity formed inside the droplets by capillary waves. Su...
Article
Fast contact-line motion of a droplet spreading on a solid substrate under the electrowetting effect generates strong capillary waves on the droplet's surface. The capillary waves may be strong enough to induce ejection of a satellite droplet from the primary one. In this study, we show that the size of the satellite droplet and the ejection time a...
Article
Full-text available
Facing shortages of personal protective equipment, some clinicians have advocated the use of barrier enclosures (typically mounted over the head, with and without suction) to contain aerosol emissions from coronavirus disease 2019 (COVID‐19) patients. There is, however, little evidence for its usefulness. To test the effectiveness of such a device,...
Preprint
Full-text available
Soft surfaces impacted by liquid drops trap more air than their rigid counterpart. Due to the extended lifetime of this air film, the dynamics and eventual rupture of trapped air film depend on its interaction with the air cavity developed in the liquid during impact. In this work, we investigate the interaction between air cavity collapse and air...
Preprint
Full-text available
Fast contact-line motion of a droplet spreading on a solid substrate under the electrowetting effect generates strong capillary waves on the droplet's surface. The capillary waves may be strong enough to induce ejection of a satellite droplet from the primary one. In this study, we show that the size of the satellite droplet and the ejection time a...
Preprint
Full-text available
Electrowetting-on-dielectric (EWOD) is a powerful tool in many droplet-manipulation applications with a notorious weakness caused by contact-angle saturation (CAS), a phenomenon limiting the equilibrium contact angle of an EWOD-actuated droplet at high applied voltage. In this paper, we study the spreading behaviours of droplets on EWOD substrates...
Preprint
Full-text available
Facing shortages of personal protective equipment, some clinicians have advocated the use of barrier enclosures (typically mounted over the head, with and without suction) to contain aerosol emissions from coronavirus disease 2019 (COVID-19) patients. There is however little evidence for its usefulness. To test the effectiveness of such a device, w...
Article
We report instability of a superheated granular layer when a droplet is deposited on top of the layer. We find that the instability caused by evaporating vapor may trap or cause the droplet to sail away from the deposited position. The sailing motion is triggered by an unstable pressure distribution originated from fast fluidization of metallic gra...
Preprint
When a liquid droplet impacts a vibrated micro-structured surface with asymmetric topology, the liquids perform a horizontal motion during its bouncing. The moving effect is observed when the liquid is in contact with a low surface energy surface (e.g. hydrophobic) and over a wide amplitude and frequency range. We propose that the motion direction...
Article
The spreading of a sessile droplet on a solid substrate is enhanced if a non-uniform electric field is applied at the contact-line region. This so-called dielectrowetting effect holds great potential in controlling the spreading of droplets by varying the strength of the electric field. In this paper, we experimentally and theoretically study the e...
Article
Additive manufacturing for electronics is one of the world's fastest growing technologies in recent years. This new and upcoming technology has facilitated many innovative applications and high commercialization of metallic nanoparticle inks. A robust and novel induction sintering technique is proposed to solve the major challenges faced by the cur...
Article
Full-text available
A liquid droplet hovering on a hot solid surface is commonly referred to as a Leidenfrost droplet. In this study, we discover that a Leidenfrost droplet spontaneously performs a series of distinct oscillations as it shrinks during the span of its life. The oscillation first starts out erratically, followed by a stage with stable frequencies, and fi...
Article
Full-text available
Human voice recognition system (VRS) is a prerequisite for voice-controlled human-machine interfaces (HMIs). In order to avoid interference from unexpected background noises, skin-attachable VRSs are proposed to directly detect physiological mechano-acoustic signals based on the vibrations of vocal cords. However, the sensitivity and response time...
Poster
Full-text available
Welcome to the First Rencontres du Vietnam on Soft Matter Science. The conference will be held in the International Centre for Interdisciplinary Science Education (ICISE), a unique science and education institution located in the coastal city of Quy Nhon, Vietnam. ICISE was built with an ambitious objective focusing on developing science and educat...
Poster
Full-text available
Welcome to the First Rencontres du Vietnam on Soft Matter Science. The conference will be held in the International Centre for Interdisciplinary Science Education (ICISE), a unique science and education institution located in the coastal city of Quy Nhon, Vietnam. ICISE was built with an ambitious objective focusing on developing science and educat...
Article
A droplet initially overstretched on a solid substrate pulls back to lower the contact area and may jump away from the substrate. The condition to realize such macroscopic behaviors is often dictated by microscopic characteristics, such as contact-line pinning, in nontrivial ways. Here we theoretically and experimentally reveal the hidden contribut...
Article
Full-text available
Carbon nanotubes (CNTs) are 1-dimensional (1D) and flexible nanomaterials with high electric conductivity and a high aspect ratio. These features make CNTs highly suitable materials for the fabrication of flexible electronics. CNTs can also be made into dispersions which can be used as the feedstock material for droplet-based 3D printing technologi...
Article
The three‐dimensional (3D) printed electronics additive manufacturing industry sector has grown substantially in the past few years, and there is increasing demand for different types of metallic nanoparticle inks in electronics printing for various applications. Metallic nanoparticle inks are commonly used for fabricating conductive tracks and pat...
Article
Full-text available
We showed that efficient mixing of fluid flows at microscales can be achieved by a simple type of micromixers based on microporous structures. We used sugar particles as templates for fabricating the microporous structures. We quantitatively studied the relation between the mixing performance and the characteristics of the microporous structures, a...
Article
Droplets partially submersed in an immiscible liquid pool attract each other. We experimentally study the interaction of floating droplets containing aqueous solution of a volatile liquid. A droplet affects its neighbors by generating a vapor gradient to the surrounding and responds by evaporating asymmetrically over its exposed cap. We show that t...
Article
We examine the contact line friction coefficient of viscous droplets spreading and retracting on solid surfaces immersed in ambient oil. By using the electrowetting effect, we generate a surface tension imbalance to drive the spreading and the retracting motion of the three-phase contact line (TCL). We show that neither the driving force intensity...
Article
A compound droplet consisting of water and silicone oil either spreads or splashes upon impacting a solid surface. We show that the transition from spreading to splashing of this type of compound droplet can be changed by varying the volumetric oil ratio in the droplets. In the spreading regime, we observe a surprising emergence of two lamellas spr...
Article
Full-text available
Boiling is a key heat transfer process for a variety of power generation and thermal management technologies. We show that nanopillar arrays fabricated on a substrate enhance both the critical heat flux (CHF) and the critical temperature at CHF of the substrate and thus, effectively increase the limit of boiling before the boiling crisis is trigger...
Article
Full-text available
Droplet spreading on substrates by electrowetting exhibits either of the two transient behaviours: one characterised by contact line oscillation, and the other one by slow spreading dynamics. The transition between these behaviours remains elusive due to the current limited understanding of the spreading dynamics on the hydrodynamical and electrica...
Article
The mass transfer of analytes is a major limiting factor of electrochemical response at vertically-aligned carbon nanotube nanoelectrode arrays (VCNs). In this study, the dependence of the mass transfer coefficient on the array diameter and force convection is studied experimentally. The mass transfer coefficient is shown to increase 2 folds by red...
Conference Paper
There are growing interests among researchers to use additive manufacturing technologies for on-demand fabrication of functional electronic components and circuitries. The conductive ink is one of the most important components in 3D printed electronics, in which the material properties of the ink determine the mechanical and electrical properties o...
Article
Utilization of carbon nanotubes (CNTs) in fabrication of electrodes for electrochemical detection often faces a conflicting goal: achieving both high response current and high mass transfer coefficient. Typically, electrodes made in a form of CNT ensembles offer high response current as a result of the large number of CNTs. However, these electrode...
Article
Full-text available
We report the formation of a thin liquid film of pre-determined shape that is achieved through wetting of water on a silicon surface patterned with aligned carbon nanotube arrays or CNT webs. We measured the profiles of liquid films on two types of silicon substrate surfaces (namely, with and without a patterned CNT web) using monochrome interferom...
Article
Wearable and flexible pressure sensor is essential to the realization of personalized medicine through continuously monitoring an individual’s state of health and also the development of highly intelligent robot. A flexible, wearable pressure sensor is fabricated based on novel SWNT/tissue paper through a low-cost and scalable approach. The flexibl...
Article
Full-text available
The Leidenfrost transition leads a boiling system to the boiling crisis, a state in which the liquid loses contact with the heated surface due to excessive vapor generation. Here, using experiments of liquid droplets boiling on a heated surface, we report a new phenomenon, termed oscillating boiling, at the Leidenfrost transition. We show that osci...
Article
A timely book, titled ‘Standards, Quality Control, and Measurement Sciences in 3D Printing and Additive Manufacturing’ has been published to discuss the bottleneck issues when adopting 3D printing in manufacturing. This book review provides some personal thoughts and discussions on the new book.
Article
Full-text available
There is a gap between 3D Printing’s fast pace of development and the acceptance of 3D Printing technologies by other industries and applications. This hesitation comes mostly from unanswered questions about the consistency, reproducibility, and quality of 3D printed products. Although the list of excellent examples demonstrating its potential keep...
Article
This paper describes the design, fabrication and characterization of a microchannel-based strain sensor using flexible material. The work explores the use of additive manufacturing, also known as 3D printing, to fabricate the sensor in easy and cost-effective way. It is shown that 3D printing can print complex designs with ease and fabricate object...
Article
Full-text available
Fabrication of fully functional devices is one of the ultimate goals of additive manufacturing technology. In order to achieve this goal, a critical step is to fabricate electronic components using fully additive methods. Although there are still numerous roadblocks that need to be overcome towards this goal, research activities in the field of add...
Conference Paper
In recent years, there is a growing interest among researchers and engineers to use additive manufacturing for fabrication of functional electronic components embedded in three-dimensional (3D) complex structures. Additive manufacturing allows on-demand, highly customised fabrication of low-cost, low-volume electronics on flat surfaces or embedded...
Article
Full-text available
There have been significant advancements in the field of additive manufacturing in the past decades. Current technologies in this field allow fabrications of not only complex physical prototypes but also functional electronic components and circuitries. It is now possible to fabricate simple circuits embedded with several kinds of passive component...
Conference Paper
Additive manufacturing has reached a certain level of maturity that not only allows fabrication of objects used for prototyping purposes but also starts penetrating other industries, e.g., the electronics industry. Numerous simple electronic components can now be fabricated using the "fully additive" method, which refers to those that only involve...
Article
Full-text available
Carbon nanotubes have been widely used as test channels to study nanofluidic transport, which has been found to have distinctive properties compared to transport of fluids in macroscopic channels. A long-standing challenge in the study of mass transport through carbon nanotubes (CNTs) is the determination of flow enhancement. Various experimental i...
Article
Mixing of fluids in microchannels is a crucial yet challenging task in lab-on-a-chip devices. Here we demonstrate a mixing enhancement method of two streams of fluids based on actuation of a single micropillar embedded with paramagnetic nanoparticles. The actuation is controlled by an external rotating magnetic field and has variable frequency up t...
Article
Full-text available
We experimentally determine the phase diagram for impacting ethanol droplets on a smooth, sapphire surface in the parameter space of Weber number $\mathit{We}$ versus surface temperature $T$ . We observe two transitions, namely the one towards splashing (disintegration of the droplet) with increasing $\mathit{We}$ , and the one towards the Le...
Article
Full-text available
We report experimental and theoretical results on a ballistic energy-conversion method based on a rotary atomizer working with a droplet acceleration-deceleration cycle. In a rotary atomizer, liquid is fed onto the center of a rotating flat surface, where it spreads out under the action of the centrifugal force and creates “atomized” droplets at it...
Article
Full-text available
A droplet impinging on a sufficiently heated surface may be cushioned by its own vapor and never touches the surface. In prior work, the transition to this so-called Leiden- frost regime was only qualitatively described as an abrupt change between the “contact-boiling” regime, which is characterized by violent boiling behaviors, and the Leidenfrost...
Article
Full-text available
The law of the wall and the log law rule the near-wall mean velocity profile of three-dimensional turbulent flows. These well-known laws, which are validated by legions of experiments and simulations, may be universal. Here, using a soap-film channel, we report the first experimental test of these laws in quasi-two-dimensional turbulent channel flo...
Article
Full-text available
When a drop impacts a surface, a dimple can be formed due to the increased air pressure beneath the drop before it wets the surface. We employ a high-speed color interferometry technique to measure the evolution of the air layer profiles under millimeter-sized drops impacting hydrophobic micropatterned surfaces for impact velocities of typically 0....
Article
Full-text available
Droplets impacting on a superheated surface can either exhibit a contact boiling regime, in which they make direct contact with the surface and boil violently, or a film boiling regime, in which they remain separated from the surface by their own vapor. The transition from the contact to the film boiling regime depends not only on the temperature o...
Conference Paper
Full-text available
We present the experimental results of an energy conversion system based on a rotary atomizer and the streaming current phenomenon. The advantage of using a rotary atomizer instead of a channel or membrane micropore as in conventional pressure-driven approached is that the centrifugal force exerted on the fluid on a smooth and large surface will av...
Article
Full-text available
We study drop impact on a deep pool of the same fluid, with an emphasis on the air layer trapped under the droplets from its formation to its rupture. The penetration velocity of the air layer at a very short time scale prior to its rupture is shown, using an energy argument and experimental verification, to be one-half of the impact velocity. We t...
Article
Full-text available
We investigate the levitation of a drop gently deposited onto the inner wall of a rotating hollow cylinder. For a sufficient velocity of the wall, the drop steadily levitates over a thin air film and reaches a stable angular position in the cylinder, where the drag and lift balance the weight of the drop. Interferometric measurement yields the thre...
Article
Full-text available
When a droplet impacts upon a surface heated above the liquid's boiling point, the droplet either comes into contact with the surface and boils immediately (contact boiling), or is supported by a developing vapor layer and bounces back (film boiling, or Leidenfrost state). We study the transition between these characteristic behaviors and how it is...
Article
Full-text available
At impact of a liquid drop on a solid surface an air bubble can be entrapped. Here we show that two competing effects minimize the (relative) size of this entrained air bubble: For large drop impact velocity and large droplets the inertia of the liquid flattens the entrained bubble, whereas for small impact velocity and small droplets capillary for...
Article
Full-text available
Although the cardinal attribute of turbulence is the velocity fluctuations, these fluctuations have been ignored in theories of the frictional drag of turbulent flows. Our goal is to test a new theory that links the frictional drag to the spectral exponent α, a property of the velocity fluctuations in a flow. We use a soap-film channel wherein for...
Article
Full-text available
A drop impacting on a solid surface deforms before the liquid makes contact with the surface. We directly measure the time evolution of the air layer profile under the droplet using high-speed color interferometry, obtaining the air layer thickness before and during the wetting process. Based on the time evolution of the extracted profiles obtained...
Article
Full-text available
At the impact of a liquid droplet on a smooth surface heated above the liquid's boiling point, the droplet either immediately boils when it contacts the surface ("contact boiling"), or without any surface contact forms a Leidenfrost vapor layer towards the hot surface and bounces back ("gentle film boiling"), or both forms the Leidenfrost layer and...
Article
Full-text available
We derive the leading-order equations that govern the dynamics of the flow in a falling, free-standing soap film. Starting with the incompressible Navier–Stokes equations, we carry out an asymptotic analysis using parameters that correspond to a common experimental setup. We account for the effects of inertia, surface elasticity, pressure, viscous...
Article
Full-text available
Two aspects of turbulent flows have been the subject of extensive, split research efforts: macroscopic properties, such as the frictional drag experienced by a flow past a wall, and the turbulent spectrum. The turbulent spectrum may be said to represent the fabric of a turbulent state; in practice it is a power law of exponent \alpha (the "spectral...
Article
Full-text available
It is widely thought that in steady, gravity-driven, unobstructed soap-film flows, the velocity increases monotonically downstream. Here we show experimentally that the velocity increases, peaks, drops abruptly, then lessens gradually downstream. We argue theoretically and verify experimentally that the abrupt drop in velocity corresponds to a Mara...