열유체공학 연구실에서는 열전달, 유체역학 해석에 기초하여, 바이오매스 공정시스템, 철강 소둔로 시스템, 발전소 시스템 등 다양한 시스템의 열유동에 대해 분석하고 있습니다. 각 시스템에 대한 이론해석, 시뮬레이션, CFD 해석을 수행하고 있으며, 산업체가 필요로 하는 전문인력을 지속적으로 배출하고 있습니다.

Numerical study on particle behavior in a Y-junction mixer for supercritical water hydrolysis

Three-dimensional simulation of droplet breakup and evaporation in attemperator

Control of Particle Size in Flame Spray Pyrolysis of Tb–doped Y2O3 for Bio-Imaging

Investigation of the Synergistic Effect of Sonolysis and Photocatalysis of Titanium Dioxide for Organic Dye Degradation

Experimental study on splash phenomena of liquid jet impinging on a vertical wall

Transient analysis of attemperator enthalpy balance based on the commissioning data of a coal-fired steam power plant

Optimization of pulsed voltage waveform for electrohydrodynamic jetting on-demand

One-dimensional simulation for attemperator based commissioning data of coal-fired steam power plant

Effects of geometry and operating conditions on hydrogen productivity of a fuel cell reformer

Modeling of sessile droplet oscillation on electrohydrodynamic jetting nozzle at constant back pressure

Resonant oscillation phenomena of a sessile droplet on electrohydrodynamic jetting nozzle

Nanosecond laser ablation of silver nanoparticle film

Time resolved imaging of electrohydrodynamic jetting on demand induced by square pulse voltage

Deposit Pattern of Inkjet Printed Pico-liter Droplet

Metal nanoparticle direct inkjet printing for low-temperature 3D micro metal structure fabrication

Onset condition of pulsating cone-jet mode of electrohydrodynamic jetting for plane, hole, and pin type electrodes

Assembly of Acircular SnO2 Rod using Optical Tweezers and Laser Curing of Metal Nanoparticles

Manipulation of Nano Devices with Optical Tweezers

Evaporation of Inkjet Printed Pico-liter Droplet on Heated Substrates with Different Thermal Conductivity

Experimental Study on Spreading and Evaporation of Inkjet Printed Pico-liter Droplet on a Heated Substrate

High resolution selective multilayer laser processing by nanosecond laser ablation of metal nanoparticle films

Fabrication of Multilayer Passive and Active Electric Components on Polymer using Inkjet Printing and Low Temperature Laser Processing

Nanosecond laser ablation of gold nanoparticle films

Damage-free Low Temperature Pulsed Laser Printing of Gold Nanoinks On Polymers

Compressible flow of liquid in standing wave tube

An experimental investigation of microresistor laser printing with gold nanoparticle-laden inks

In tandem deposition and sintering of printed gold nanoparticle inks induced by continuous Gaussian laser irradiation

Conductor microstructures by laser curing of printed gold nanoparticle ink

Manufacturing of nanoscale thickness gold lines by laser curing of a discretely deposited nanoparticle suspension

Infrared thermal velocimetry in MEMS-based fluidic devices

Infrared thermal velocimetry for nonintrusive flow measurement in silicon microfluidic devices

Microstructuring by printing and laser curing of nanoparticle solutions

Jaewon CHUNG

The laser-based curing of printed nanoparticle ink to create microlines (resistors) of electrical resistivity approaching that of bulk gold was investigated. The present work relies on laser absorption in both the nanoparticle ink and the sintered gold layer, as well as the transport of thermal energy in the substrate and the resulting solvent vaporization and nanoparticle deposition and sintering. The morphology and electrical properties of the gold line can be controlled by modulating the spatial distribution of the laser beam intensity. Based on the understanding of the underlying physics, a process that circumvents a serious drawback on the functionality of cured gold microlines is produced. Microconductors with resistivity approaching that of bulk gold are produced, while loss of gold nanoparticles and cross sectional nonuniformities are avoided.

In this work, the spreading and evaporation of 2–70pL droplet (17–50μm diameter) of water and ethylene glycol jetted by drop-on-demand piezo-driven jetting head on the heated substrate are studied. According to the experimental results, the interfacial oscillation phenomena of water droplet whose Ohnesorge number (Oh) is about 10 −2 is similar to that in inviscid impact driven region, while that of ethylene glycol droplet (Oh ≈10 −1 ) is similar to that in highly viscous impact driven region followed by capillary driven extra spreading. In addition, various time scales used for nano/micro-liter droplets agree well with the times for interfacial oscillation, viscous damping, extra wetting, and evaporation in pico-liter droplets. In the case of water droplet, the spreading processes end before the evaporation becomes significant. However, in the case of highly viscous ethylene glycol droplet, the extra wetting overlaps the …

Experimental study on spreading and evaporation of inkjet printed pico-liter droplet on a heated substrate

In this letter, the process of printing and laser curing of nanoparticle solutions is presented. A liquid solvent is employed as the carrier of gold nanoparticles (the material of interest in this study) possessing a low melting temperature compared to that of bulk gold. Using a specifically designed printing system, the gold nanoparticle solution is deposited on a substrate and cured with laser radiation. In this manner, the potential of writing gold structures on temperature sensitive substrates is demonstrated. The interaction between the laser radiation and nanoparticles drives the solvent evaporation and controls the quality of the microstructures printing process. The latter is also affected by thermocapillary flow at the free surface, developing during the curing process. An optical method for estimating the curing times is also developed and discussed.

Inkjet printing of functional materials is a key technology toward ultra-low-cost, large-area electronics. We demonstrate low-temperature 3D micro metal structure fabrication by direct inkjet printing of metal nanoparticles (NPs) as a versatile, direct 3D metal structuring approach representing an alternative to conventional vacuum deposition and photolithographic methods. Metal NP ink was inkjet-printed to exploit the large melting temperature drop of the nanomaterial and the ease of the NP ink formulation. Parametric studies on the basic conditions for stable 3D inkjet printing of NP ink were carried out. Furthermore, diverse 3D metal microstructures, including micro metal pillar arrays, helices, zigzag and micro bridges were demonstrated and electrical characterization was performed. Since the process requires low temperature, it carries substantial potential for fabrication of electronics on a plastic substrate.

The low temperature fabrication of passive (conductor, capacitor) and active (field effect transistor) electrical components on flexible polymer substrate is presented in this paper. A drop-on-demand (DOD) ink-jetting system was used to print gold nano-particles suspended in Alpha-Terpineol solvent, PVP (poly-4-vinylphenol) in PGMEA (propylene glycol monomethyl ether acetate) solvent, semiconductor polymer (modified polythiophene) in chloroform solution to fabricate passive and active electrical components on flexible polymer substrates. Short pulsed laser ablation enabled finer electrical components to overcome the resolution limitation of inkjet deposition. Continuous argon ion laser was irradiated locally to evaporate the carrier solvent as well as sinter gold nano-particles. In addition, selective ablation of multilayered gold nanoparticle film was demonstrated using the novel SPLA-DAT (selective pulsed laser …

Fabrication of multilayer passive and active electric components on polymer using inkjet printing and low temperature laser processing

Ablation of self-assembled monolayer protected gold nanoparticle films on polyimide was explored using a nanosecond laser. When the nanoparticle film was ablated and subsequently thermally sintered to a continuous film, the elevated rim structure by the expulsion of molten pool could be avoided and the ablation threshold fluence was reduced to a value at least ten times lower than the reported threshold for the gold film. This could be explained by the unusual properties of nanoparticle film such as low melting temperature, weak bonding between nanoparticles, efficient laser energy deposition, and reduced heat loss. Finally, submicron lines were demonstrated.

By employing continuous Gaussian laser irradiation in tandem with a specifically designed drop-on-demand jetting system, nanoparticle inks were printed and sintered on glass substrate. A toluene solvent is employed as the carrier of gold nanoparticles possessing a lower melting temperature than that of bulk gold. Marangoni flow due to radial surface tension gradient combined with a moving substrate displaces nanoparticle ink in front of and around the laser spot. Experiments were carried out changing incident laser power, focused beam waist, and translation speed, and resulting phenomena at different conditions were explained. Strong coalescence occurred from 9000–14000 W/cm 2 , and a gold line with 8 μm of width was demonstrated.

In-tandem deposition and sintering of printed gold nanoparticle inks induced by continuous Gaussian laser irradiation

The present work is focused on a novel method for the manufacturing of electric microconductors for semiconductors and other devices. Three different technologies are combined in this technique: controlled (drop on demand) printing, laser curing, and the employment of nanoparticles of matter, possessing markedly different properties (here, melting point) than their bulk counterparts. A modified on demand ink jet process is utilized to print electrically conducting line patterns from a suspension of gold nanoparticles in toluene. Microdroplets of 60–100 μm diameter are generated and deposited on a moving substrate such that the droplets form continuous lines. Focused laser irradiation is utilized in order to evaporate the solvent, melt the metal nanoparticles in the suspension, and sinter the suspended particles to form continuous, electrically conducting gold microlines on a substrate. The ultrafine particles in the …

In this study, pulsed laser based curing of a printed nanoink (nanoparticle ink) combined with moderate and controlled substrate heating was investigated to create microconductors at low enough temperatures appropriate for polymeric substrates. The present work relies on (1) the melting temperature depression of nanoparticles smaller than a critical size, (2) DOD (drop on demand) jettability of nanoparticle ink, and (3) control of the heat affected zone induced by pulsed laser heating. In the experiments, gold nanoparticles of diameter dissolved in toluene solvent were used as ink. This nanoink was printed on a polymeric substrate that was heated to evaporate the solvent during or after printing. The overall morphology of the gold microline was determined by the printing process and controlled by changing the substrate temperature during jetting. In addition, the printed line width of about at the room temperature …

Damage-free low temperature pulsed laser printing of gold nanoinks on polymers

Ablation of gold nanoparticle films on polymer was explored using a nanosecond pulsed laser, with the goal to achieve feature size reduction and functionality not amenable with inkjet printing. The ablation threshold fluence for the unsintered nanoparticle deposit was at least ten times lower than the reported threshold for the bulk film. This could be explained by the combined effects of melting temperature depression, lower conductive heat transfer loss, strong absorption of the incident laser beam, and the relatively weak bonding between nanoparticles. The ablation physics were verified by the nanoparticle sintering characterization, ablation threshold measurement, time resolved ablation plume shadowgraphs, analysis of ablation ejecta, and the measurement and calculation of optical properties. High resolution and clean feature fabrication with small energy and selective multilayer processing are demonstrated.

2006-09-26 Assigned to REGENTS OF THE UNIVERSITY OF CALIFORNIA, THE reassignment REGENTS OF THE UNIVERSITY OF CALIFORNIA, THE ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: GRIGOROPOULOS, CONSTANTINE P., CHUNG, JAEWON, KO, SEUNG-HWAN, PAN, HENG

Maskless nanofabrication of electronic components

This paper presents an experimental investigation of the novel thermal manufacturing process of printing and laser curing of nanoparticle-laden inks that can produce functional microstructures such as electronic microresistors and interconnections for semiconductors and other devices. Of specific interest are the complex and interweaved transport phenomena involved, focusing on the absorption and diffusion processes of irradiated laser energy influencing solvent vaporization, the nanoparticle curing process, the substrate, and the final quality of the produced resistor. Parametric studies of the thermal process together with extensive microscopy analysis of the topography and resistivity measurements piece together a better understanding of the underlying physics and aid the development of the technology.

In this work, the evaporation phenomena of 20–45 picoliter water droplet (i.e. 50–65 μm diameter) on heated substrates with different thermal conductivity are studied experimentally. The effect of thermal conductivity of substrates and inter-distance between jetted droplets on the evaporation is investigated. In addition, the model to predict evaporation rate of the picoliter droplet on different substrates at a heated condition is developed using approximations for picoliter droplet.

Evaporation of inkjet printed pico-liter droplet on heated substrates with different thermal conductivity

Herein, we report the effect of sonoluminescence and an initial dye concentration on the sonophotocatalysis of TiO 2 for the degradation of eosin B, a textile dye. We first investigated the light illuminated during ultrasound irradiation (sonoluminescence) by photographic images, a radical indicator (luminol), and photoluminescence spectra of the detection range of 300–1050 nm. Next, we examined the synergistic effect of sonolysis on photocatalysis by comparing the dye degradation of sonophotocatalysis to that of individual contributions of sonolysis and photocatalysis. Since it was found that the synergist effect is highly engaged with a dye concentration and sonication power, we conducted the comparison test in different concentrations of eosin B (5 and 20 mg/L) and ultrasound powers (35.4, 106.1, and 176.8 W/cm 2 ). When the concentration of dyes was low, negative synergistic effects were found at all ultrasound powers, whereas at the high concentration, positive synergistic effects were observed at high ultrasound power. This difference in synergistic effects was explained by the influence of ultrasound on dynamics of dye adsorption on the TiO 2 surface.

Investigation of the synergistic effect of sonolysis and photocatalysis of titanium dioxide for organic dye degradation

In this work, electrohydrodynamic (EHD) jetting phenomena were observed for three different types of bottom electrode (plane, hole, pin) at constant back pressure condition of the reservoir. Especially, we have focused on the measurement and numerical prediction of the onset voltage for pulsating Taylor cone jetting, changing glass capillary nozzle diameter (outer diameter: 16–47 μ m⁠), hydrostatic back pressure head in the reservoir, and the distance between the nozzle and the bottom electrode to provide design information on the EHD multinozzle head.

For forming a fine structure of a desired material, nanopar ticles of the same material are prepared in a suspension. A layer of the Suspension is applied by a drop-on-demand printing system to a substrate. At least part of the layer is exposed to laser light for melting the nanoparticles at least partially. Upon solidification, the molten particles are sin tered together to form the desired structure. Due to the low melting point of nanoparticles as compared to the melting point of bulk material, this procedure avoids damage to the substrate and provides a better control over the structure generation process. It can be used for generating metallic and non-metallic structures on various Substrates. The laser light may have non-Gaussian intensity distribution or can combine multiple beams of Gaussian and non-Gaussian distribution for improving the quality of the generated structure, or it may be pulsed for improved control of the …

Method for producing a structure using nanoparticles

The authors have demonstrated organic thin film transistors (OTFTs) based on the ink-jet printed electrodes in which a reduced channel length is accomplished by laser ablation. Laser ablation on the dried silver nanoparticle electrode formed by ink-jet printing effectively shortened the channel length down to 5 μ m⁠, which is difficult to achieve by ink-jet printing alone. Reducing the channel length using this hybrid technique also allows them to observe the contact resistance effect in the OTFTs, which involves the printed silver nanoparticle electrode of a lower work function with respect to the ionization energy of the organic semiconductor.

Organic thin film transistors with ink-jet printed metal nanoparticle electrodes of a reduced channel length by laser ablation

Nanosecond laser ablation of polyvinylpyrrolidone (PVP) protected silver nanoparticle (20 nm diameter) film is studied using a frequency doubled Nd:YAG nanosecond laser (532 nm wavelength, 6 ns full width half maximum pulse width). In the sintered silver nanoparticle film, absorbed light energy conducts well through the sintered porous structure, resulting in ablation craters of a porous dome shape or crown shape depending on the irradiation fluence due to the sudden vaporization of the PVP. In the unsintered silver nanoparticle film, the ablation crater with a clean edge profile is formed and many coalesced nanoparticles of 50 to 100 nm in size are observed inside the ablation crater. These results and an order of magnitude analysis indicate that the absorbed thermal energy is confined within the nanoparticles, causing melting of nanoparticles and their coalescence to larger agglomerates, which are removed …

The deposit pattern of an evaporating picoliter droplet is studied changing the solvents (water, diethylene glycol, and formamide), mixing composition of the solvents and substrate temperature. When depinning occurs in the early stage of the evaporation period, concentrated solute (or partially deposited solute, if any) also retracts with the receding droplet, resulting in dome shaped deposit patterns. When pinning is maintained during most of the evaporation period, either a ring deposit or a relatively uniform deposit is obtained depending on the type of solvent and heating condition. These results are explained by interplay of (1) radial outward flow due to the strong evaporation flux at the contact line of a sessile droplet, (2) inward Marangoni flow due to evaporative cooling and solvent concentration gradient, and (3) solute mixing by diffusion in liquid.

Deposit pattern of inkjet printed pico-liter droplet

Electrohydrodynamic (EHD) printing is receiving much attention due to its high resolution printing capability, as well as its many advantages such as reduced manufacturing steps and non-toxic, flexible processes. However, many issues need be resolved before it can be widely used. In this work, to demonstrate EHD printing on demand, square pulse voltage signals are applied between a hole-type electrode and the nozzle supplied with working fluid from a reservoir at constant pressure. Continuous fine jet, pulsating fine jet, and pulsating droplet modes are observed depending on the voltage signal. To obtain the optimum voltage pulse duration, the change in the jetting start time is measured by varying the voltage configurations and hydrostatic pressure applied to the nozzle. Among the modes, the pulsating droplet mode is studied in detail for various voltage signals. Futhermore, the printing is demonstrated using …

열유체공학 연구실

교수님 소개

정재원

연구실 소개

연구실 키워드

알럼나이가 간 회사

연구실 지원 방법

대우 조건

연도별 논문 인용수

저널 & 학회 논문 출판 수

연구실 논문 목록

Numerical study on particle behavior in a Y-junction mixer for supercritical water hydrolysis

Three-dimensional simulation of droplet breakup and evaporation in attemperator

Control of Particle Size in Flame Spray Pyrolysis of Tb–doped Y2O3 for Bio-Imaging

연구실 보유 특허

대학별 입시끈

우리 연구실 모집

교수님 소개

정재원

연구실 키워드

알럼나이가 간 회사

연구실 지원 방법

대우 조건

연도별 논문 인용수

저널 & 학회 논문 출판 수

연구실 논문 목록

Numerical study on particle behavior in a Y-junction mixer for supercritical water hydrolysis

Three-dimensional simulation of droplet breakup and evaporation in attemperator

Control of Particle Size in Flame Spray Pyrolysis of Tb–doped Y2O3 for Bio-Imaging

연구실 보유 특허

최근 3년간 연구실적 높은 연구실

대학별 입시끈

우리 연구실 모집