• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.666-669
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• 2008

Droplet in miniaturized microfluidic systems have received much focused attention recently. In this work, electrical charging phenomenon of a conducting water droplet on the electrode under the dc electric field is studied and using this phenomenon droplet actuation method for microreactor applications is experimentally demonstrated. To find effects of key factors, the effects of electric field, medium viscosity, and droplet size are investigated. A scaling law of charging for the conducting droplet is derived from the experimental results. Unlike the case of a perfect conductor, the estimated amount of electrical charge ($Q_{est}$) of a water droplet is proportional to the 1.59 power of the droplet radius (R) and the 1.33 power of the electric field strength (E). (For a spherical perfect conductor, Q is proportional to R2 and E.) It is thought that the differences are mainly due to incomplete charging of a water droplet resulted from the combined effect of electrochemical reaction at electrode and the relatively low conductivity of water. Using this phenomenon, we demonstrate the transport of the charged droplet and fusion of two oppositely-charged droplets. When electric field is subjected sequentially on the electrode, the charged droplet is transported on the electrode. For the visualization of fusion of charged droplets, the precipitation reaction is used. When subjected to a DC voltage, two droplets charged are moving and merging toward each other due to the Coulombic force and chemical reaction is simultaneously occurred by coalescence of droplets. It may be due to the interchange effect of charge. It is shown that the droplet can be used for microreactor where transporting, merging etc. of reagents constitute unit operation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.571-572
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• 2013

• Journal of the Korean Society of Visualization
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• v.10 no.1
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• pp.9-14
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• 2012

In this study, a piezoelectric inkjet nozzle with a rectangular shaped channel has been developed, and the characteristics of droplet formation have been investigated according to the variation of pulse widths in bipolar waveform. The channel of the nozzle was fabricated transparently by a precision machining technique. A tantalum membrane which was attached to a piezoelectric material covers the channel. By applying two types of bipolar waveforms to the piezoelectric actuators, droplet formation through the nozzle was monitored by a CCD camera. For the variety of the first and second pulse widths in the bipolar waveforms, the regimes of single and double droplet formations are presented. The change of droplet velocity which depends on the pulse width and the type of waveform is also discussed.

• Journal of the Korean Society of Visualization
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• v.6 no.1
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• pp.47-52
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• 2008

The present study has focused on the characteristics of droplet formation from an inkjet nozzle driven by a piezoelectric actuator. As an operating fluid, ethylene glycol was used and the physical properties of it such as viscosity, surface tension, contact angle and shear stress were measured. During the experiments, various temperatures and driving voltages are imposed on a capillary tube. These conditions result in a proper drive condition or an overdrive condition. In case of the proper drive condition, an image processing technique is applied to measure the diameter of a single free drop. As a result, the size of droplet is increased when the driving voltage is increased from 160 V to 190 V at 25$^{\circ}C$ In the overdrive condition where temperature or driving voltage becomes higher than the proper drive condition, satellites and the misdirected jets happen.

• Journal of Sensor Science and Technology
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• v.21 no.1
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• pp.53-58
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• 2012

Biological and chemical assays(e.g., clinical tests for medical diagnosis) are needed to handle small liquid volume with high accuracy and high reliability. Many micro-dispensing systems using various actuation methods have been developed and applied. In this research, we confirm repeatability of the cartridge-type dispensing system with various measuring methods for guarantee of an acceptable reliability. We systematically examine the dispensed volume variation and dispense rate during 500,000 shots of sequential actuation. Using the same method, we confirm the repeatability of dispensed volume while varying operating conditions and design parameter(i.e., outlet size) of the dispensing system. Also, we examine the consistency of the dispensed volume of droplet while varying the operating pressures. Furthermore, we repeatedly measure differences between an actual dispensed volume and a target volume. According to our results, it is expected that the stable and reliable performance of our dispensing system can effectively be used in various applications containing bio-solutions.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.4
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• pp.369-375
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• 2015

This paper presents ejection of high viscosity fluids with magnetostrictive inkjet printhead(Magjet), which is not common with any other printhead. The MagJet uses a magnetostrictive material, Terfenol-D rod with 10-mm in diameter and 50-mm in length, as an actuation mechanism. It has been known that high viscosity is often an obstacle in ejecting small and mono-disperse droplets. We calculated required pressure with fluidic inertia (Bernoulli equation) and viscous loss (Hagen Poiseuille equation). The required pressure for ejecting a droplet is 1300kPa. The generated force and displacement with Terfenol-D rod are estimated to be 480N (2600kPa) and $28{\mu}m$, respectively. It was enough that Magjet eject high viscosity fluid (Max 1000cP). The experiments are performed to eject the high viscosity fluid with Magjet. The ejection of high viscosity fluids is successful with the aid of Terfenol-D's high performance.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.7 s.238
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• pp.970-975
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• 2005

This paper presents a novel microgenerator of $CO_2$ (carbon dioxide) gas. $NaHCO_3$ (sodium bicarbonate) in a chamber is decomposed by the underlaid microheater. Alternatively, water droplet is caged by paraffin layer and released by heating. The released water dissolve HOC(COOH)$(CH_2COOH)_2$ (citric acid) powder and then, $NaHCO_3$ reacts with the solubilized HOC(COOH)$(CH_2COOH)_2$ and $CO_2$ is produced. Micropumps actuated by $CO_2$ generation were fabricated. A portable micro cell incubator of which pH is controlled by the produced $CO_2$ is also presented as one of the further applications.