• 한국분무공학회지
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• 제26권2호
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• pp.73-80
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• 2021

Evaporation characteristics of single butanol gel fuel were investigated in different mass ratios of gellant and ambient temperatures. Gel fuel was made by adding the pure water and hydroxypropylmethyl cellulose (HPMC) into the 1-butanol. Increase of viscosity was observed when the loading of HPMC increased. The evaporation process of gel droplet could be divided into three stages: droplet heating, micro-explosion and crust formation. Elevation of ambient temperature helped boost the evaporation in all experimental cases, but the effect was mitigated when the mass ratio of HPMC increased. Increase of HPMC weight ratio reduced the evaporation rate.

• Journal of Korean Society for Atmospheric Environment
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• 제24권E1호
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• pp.54-62
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• 2008

Microbeam PIXE, often called micro-PIXE, is one of powerful tools for analyzing a wide range of elements for various samples. Moreover, it has important applications of interest to the atmospheric science. In the present study, a qualitative elemental imagination for various atmospheric environmental species was attempted using micro-PIXE. Especially, in combination with a novel individual droplet collection method and the micro-PIXE analytical technique, the chemical specification of various individual atmospheric samples could be carried out. Here, we briefly introduce the results of an application of micro-PIXE to the study of atmospheric environment. The detailed spatial resolution of multiple elements for various samples like individual ambient particles, individual raindrops, individual fog droplets, and individual snow crystals could be successfully achieved by scanning 2.6 MeV $H^+$ micro beam ($1{\sim}2{\mu}m$) accelerated by 3 MeV single-end accelerator.

• 한국정밀공학회지
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• 제29권8호
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• pp.913-919
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• 2012

This paper presents results for dispensing and measuring micro-particles using a pneumatic dispensing system. Particle-suspended liquid droplets were dispensed and analyzed quantitatively at various particle concentrations and applied pressures. By using a developed experimental setup, the number of particles and the particle volume ratio in sequentially dispensed droplets were measured. Hydrophilic and hydrophobic surfaces were tested to find a suitable surface for counting the number of particle. It was confirmed that the dispensed particles concentrated into the center of the droplet on the smooth CD surface after evaporation of liquid. As the applied positive pressure increased, the number of particles per droplet increased consistently and the volume fraction of particles remained constant.

• 한국분무공학회지
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• 제15권4호
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• pp.202-207
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• 2010

Mist cooling is widely employed as a cooling technique of high temperature surfaces, and it has heat transfer characteristics similar to boiling heat transfer which has the convection, nucleate and film boiling regions. In the present study, mist cooling heat transfer was experimentally investigated for the mist flow impacting on the heated surfaces of mico-fins. The mist flow was generated by supersonic vibration. Experiments were conducted under the test conditions of droplet flow rate, $Q=6.02{\times}10^{-9}{\sim}3.47{\times}10^{-8}\;m^3/s$ and liquid temperature, $T_f=30{\sim}35^{\circ}C$. From the experimental results, it is found that an increase in the droplet flow rate improves mist cooling heat transfer in the both case of smooth surface and surfaces of micro-fins. Micro-fins surfaces enhance the mist cooling heat transfer. Besides, the experimental results show that an increase in the droplet flow rate decrease the heat transfer efficiency of mist cooling.

• 한국정밀공학회지
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• 제29권9호
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• pp.1020-1025
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• 2012

In this study, we fabricated the superhydrophobic and super-water-repellent surface with the micro/nano scale structures using simple conventional silicon wet-etching technique and the black silicon method by deep reactive ion etching. These fabrication methods are simple but very effective. Also we reported the droplet impact experimental results on the micro/nano-scaled surface. There are two representative impact behaviors as "rebound" and "fragmentation". We found the transition Weber number between "rebound" and "fragmentation" statements, experimentally. Additionally, we concerned about the dimensionless spreading diameters for our super-water-repellent surface. The novel characterization method was introduced for analysis including the "fragmentation" region. As a result, our super-water-repellent surface with the micro/nano-scaled structures shows the different impact behaviors compared with a reference smooth surface, by some meaningful experiments.

• Journal of Advanced Marine Engineering and Technology
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• 제30권5호
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• pp.552-561
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• 2006

The single droplet combustion characteristics of diesel fuel and low quality oil with additive oxygenate and paraffin under high ambient temperature and atmospheric pressure were investigated in the study. The results of the study may are concluded as follows: In the combustion of diesel fuel and low quality oil droplet with additive of oxygenate and paraffin. the dimensionless droplet size of $(D/Do)^2$ was linearly decreased with time. A fuel droplet with low boiling temperature additives and in high boiling temperature base fuel evaporates and burns faster than usual base fuel. Especially. these trends were remarkably obtained by decreasing boiling point and increasing blending contents of additives in case of oxygenated agents rather than n-paraffin agents. This rapid burning may result from so-called 'micro-explosion' and its burning intensity varies with the types of additives. The results above may suggest that rapid evaporation of oxygenate additive in the middle stage of combustion can contribute much to combustion improvement of blended fuels.

• 한국분무공학회지
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• 제20권3호
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• pp.181-186
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• 2015

This study presents the dynamic wetting characteristics of an impact droplet on hole-patterned textured surfaces. The flat surfaces were manufactured by a drilling machine to generate the micro-order holes, leading to make the surface hydrophobic. Other flat surfaces were fabricated by the anodizing technique to make hydrophilic texture surfaces with a nanometer order. For hydrophilic and hydrophobic textured surfaces with similar texture area fractions, the impinging droplet experiments were conducted and compared with flat surface cases. As results, an anodized textured surface decreases apparent equilibrium contact angle and increases contact diameters, because of increase in contact area and surface energy. This is attributed to more penetration inside holes from larger capillary pressure on nanometer-order holes. On the other hand, temporal evolution of the contact diameter is smaller for the hydrophobic textured surface from less penetration on the micro-order holes.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.548-550
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• 2010

The droplet motion on a flat substrate with contact angle hysteresis is studied by solving the equations governing the conservation of mass and momentum. The liquid- gas interface is determined by an level-set method which is based on a sharp-interface representation for accurately imposing the matching or coupling conditions at the interface. The method is modified to treat the dynamic contact angle at the liquid-gas-solid interface. The computations are performed to investigate a droplet impact and merging pattern on a flat substrate to find a optimal condition in a micro-line patterning process. The effects of dynamic contact angles on droplet motion are quantified.

• 에너지공학
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• 제18권2호
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• pp.101-107
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• 2009

경유와 바이오 디젤이 혼합된 액적을 고온의 연소실에서 액적의 크기, 주위온도 그리고 각각의 혼합비율에 따라 연소특성에 미치는 영향에 대해 연구하였다. 경유에 0%, 20%, 50% 80%, 100%의 비율로 바이오 디젤을 혼합하여 다양한 크기의 액적을 만든 후 서스펜더에 매달고 970K에서 1070K까지 50K 간격으로 고온에서 자발화를 시키면서, 전체의 연소 과정을 고속 디지털 카메라로 촬영하여 점화지연, 수명시간, 전연소기간, 그리고 미소폭발 등의 연소 특성을 파악하였다. 액적의 크기가 증가하고 연소실 온도가 낮을수록 점화가 지연되었다. 경유에 대한 바이오 디젤의 혼합비율이 감소할수록 점화지연이 증가하였고 미소폭발 발생률도 증가하였다. 또한, 미소폭발이 발생하는 경우 전연소기간이 짧아짐을 확인하였다.

• Corrosion Science and Technology
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• 제9권6호
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• pp.331-337
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• 2010

This study compared the macro and micro electrochemical characteristics at the local area of welding metal on dissimilar welding parts for type 304 stainless steel (SS) and type 316L SS. The materials are used for double wall gas pipe of duel fuel engine for a ship. The various potentiodynamic experiments were performed several times in 10% ${H_2C_2O_2}{\cdot}{H_2O}$ solution using macro and micro methods, respectively. The micro electrochemical experiments conducted to resolve at local area on cross-section of dissimilar welding materials by micro-droplet cell device. The micro-droplet cell techniques can be used almost electrochemical experiments to resolve corrosion characteristics of the limited electrode area of the metallic surface between wetted spot of working electrode and tip of sharpened capillary tube. The results of macro electrochemical experiments show that resistance of active dissolution reaction at welding zone was high due to low current density by formation of passivation protection film at passive region. According to the micro electrochemical experiment, the corrosion current density of welding zone and bond zone were relatively high.