• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.702-715
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• 1990

This paper describes behaviors of two-phase open channel flow inside the flash chamber of a horizontal Multi-Stage-Flash evaporator numerically along with the experimental observations. Bubble trajectories and the velocity and temperature distributions of the liquid phase were predicted by using the particle-source-in-cell(PSI-Cell) method with the appropriate bubble motion/growth equations. Size and number of bubble nuclei embedded in the incoming liquid(brine) were taken into account as important parameters in addition to the conventional ones such as the velocity, degree of inlet superheat, inlet opening height, and the liquid level. Bubble motions, which are unsteady, appeared to be mostly determined by the buoyancy and the drag forces. The calculations, though a number of simplifying assumptions were made, reasonably simulated the hydrodynamic behaviors of the two-phase horizontal stream observed in the experiments. The simulated temperature distributions also agreed fairly well with the other's measurements. Non-equilibrium allownaces, evaluated from the simulated temperature distributions, were within the range of those obtained from the existing correlations, and reduced with the increases of the number and size of incoming bubble nuclei due to vigorous flashing.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.1
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• pp.5-12
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• 2000

As a semiconductor material for electronic devices operated under extreme environmental conditions, silicon carbides (SiCs) have been intensively studied because of their excellent electrical, thermal and other physical properties. The growth characteristics of single- crystalline 6H-SiC homoepitaxial layers grown by a thermal chemical vapor deposition (CVD) were investigated. Especially, the successful growth condition of 6H-SiC homoepitaxial layers using a SiC-uncoated graphite susceptor that utilized Mo-plates was obtained. The CVD growth was performed in an RF-induction heated atmospheric pressure chamber and carried out using off-oriented ($3.5^{\circ}$tilt) substrates from the (0001) basal plane in the <110> direction with the Si-face side of the wafer. In order to investigate the crystallinity of grown epilayers, Nomarski optical microscopy, transmittance spectra, Raman spectroscopy, XRD, Photoluninescence (PL) and transmission electron microscopy (TEM) were utilized. The best quality of 6H-SiC homoepitaxial layers was observed in conditions of growth temperature $1500^{\circ}C$ and C/Si flow ratio 2.0 of $C_3H_8$ 0.2 sccm & $SiH_4$ 0.3 sccm.

• Transactions of the Korean hydrogen and new energy society
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• v.31 no.2
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• pp.210-222
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• 2020

Hydrogen is evaluated as one of new energy sources that can overcome the limitations and pollution problems of conventional fossil fuels. Although hydrogen is free from CO₂, attention is required in NOx emission and flame stability in order to use hydrogen in existing gas fuel system. This study investigates the differences in operating characteristics and its problems to be modified when the hydrogen is used as fuel for existing domestic boilers and new heat recover boilers with water spray. When the hydrogen is used in domestic boilers, the efficiency is about 6-7% lower than methane due to higher partial vapor pressure in the exhaust gas at usual operating conditions above 60℃ in combustion chamber outlet temperature. On the other hand, the heat recovery boiler with water spray (HR-B/WS-X) is expected to achieve up to 95% efficiency, which is 12% more efficient than conventional boilers. It can also significantly reduce NOx emission by lowering the flame temperature.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.9
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• pp.2251-2258
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• 2014

In this paper, an integrated control system for removable welfare equipment disinfection is implemented. The integrated control system consisted of a hydrogen peroxide vapor supply control circuit, a sterilization chamber control circuit using low vacuum, and a washing control circuit using microbubble. A Smart-phone based remote control and monitoring system is implemented to monitor the operating status and communication status for the integrated control system. An experiment is set up to evaluate the performance of the integrated control system. The experiment result confirms that signal and operation status can transmit and receive within the control circuit. The integrated control system shows good performance in terms of sensor interface, communication state and control. In future research, the proposed control system should deploy to an actual system for trial test to prove its performance.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.447-447
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• 2010

일찍이 $SiO_2$ (Silicon dioxide) 박막은 다양한 분야에서 유전층, 부식 방지층, passivation층 등의 역할을 해왔다. 그리고 이러한 박막 공정은 대부분 진공의 환경에서 그 공정이 이루어지고 있다. 하지만 이러한 진공 system은 chamber, loadlock 그리고 펌프 등의 다양한 진공장비로 인한 생산 비용 증가, 공정의 복잡성뿐만 아니라 공정의 대면적화에 어려움을 지니고 있다. 그리고 최근 flexible display의 제조 공정에서 polymer 혹은 plastic 기판을 제조 공정에 적용시키기 위해 저온 공정이 필수적으로 요구 되고 있다. 이러한 기술적 한계를 뛰어 넘기 위해 최근 많은 연구가들은 atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD)에 대해 지속적으로 다양한 연구를 하고 있다. 본 연구에서는 remote-type의 modified pin-to-plate dielectric barrier discharge (DBD) 시스템을 이용한 $SiO_2$ 무기 박막 증착에 관해 연구하였다. $O_2$/He/Ar의 gas와 5 kV AC power (30 kHz)의 전원장치를 통해 고밀도 대기압 플라즈마를 발생시켰고, silicon precursor로는 hexamethyldisilazane (HMSD)를 사용하였다. 먼저 HMDS와 $O_2$ gas의 flow rate 변화에 따른 증착률을 조사하였고 그 다음으로 박막의 조성 및 표면 특성을 조사하였다. HMDS의 유량이 100 ~ 300 sccm으로 증가함에 따라 증착속도는 증가했다. 하지만 FT-IR을 통해 HMDS의 유량이 증가하면 반응에 참여할 산소 분자의 부족으로 인해 $-(CH_3)_X$의 peak intensity가 증가하고, -OH의 peak intensity가 점차 감소함을 관찰 할 수 있었다. 또한 증착된 박막의 표면에 particle과 불균일한 surface morphology 등을 SEM image를 통해 관찰 하였다. 산소 유량이 탄소와 관련된 많은 불순물들의 제거에 도움이 됨에도 불구하고 14 slm 이상의 산소가 반응기 내로 주입되게 되면 대기압 플라즈마의 discharge가 불안정하게 되어 공정효율을 저하시키는 요소가 되었다. 결과적으로 HMDS (150 sccm)/$O_2$ (14 slm)/He (5 slm)/Ar (3 slm)의 조건에서 약 42.7 nm/min 증착률을 가지며, 불순물이 적고 surface morphology가 깨끗한 $SiO_2$ 박막을 증착할 수 있었다.

• Korean Journal of Metals and Materials
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• v.47 no.12
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• pp.828-833
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• 2009

As a fundamental study in the development of a distillation process for ferromanganese alloy melts, the evaporation behavior of an electrolytic manganese melt under reduced pressure was investigated. The melt temperature, vacuum degree, surface area of the melt, and reaction time were considered as experimental variables. The amount of vaporized manganese increases linearly as the reaction time increases, and the evaporation of manganese was promoted by increasing the temperature and surface area of the melt. In the pressure range below the equilibrium vapor pressure of manganese, the amount of vaporized manganese per unit surface area of the melt increased sharply with a decrease of the pressure in the reaction chamber. An empirical equation for the evaporation rate of manganese was derived by regression analysis. The evaporation coefficient of manganese was determined to be approximately $3.84{\times}10^{-3}(g{\cdot}K^{1/2})/(Pa{\cdot}cm^2{\cdot}min)$ under the investigated conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.9
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• pp.909-916
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• 2015

In this study, to investigate the effect of spray behavior characteristics, we induce the mixing ratio of emulsified fuel using impinging spray. We formulate the emulsified fuel by mixing diesel and hydrogen peroxide($H_2O_2$). We set the temperature of the heating plate to $150^{\circ}C$, $200^{\circ}C$, and $250^{\circ}C$, and set the injection pressures to 400, 600, 800, and 1000bar. The surfactants for the emulsified fuel mixture, which were mixed span80 and tween80 was mixed as 9:1, were fixed to 3% of the total volume of the emulsified fuel. We set the mixing ratio of $H_2O_2$ in the emulsified fuel as emulsified fuel(EF)0, EF2, EF12, and EF22. Further, we visualize the evaporation impinging spray using the Schlieren method. Based on the results of this study, we found that a higher temperature and injection pressure of the heating plate impingement led to the active diffusion of the fuel vapor, which promoted emulsified fuel evaporation. When the emulsified fuel is utilized in an actual engine, because of the temperature-drop effect of the combustion chamber, which is due to the evaporation of $H_2O_2$ in fuel and faster mixture formation is expected to decrease the engine emissions.

• Analytical Science and Technology
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• v.14 no.5
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• pp.451-457
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• 2001

Because liquids with high molecular weight such as mineral oil have low vapor pressure at room temperature, it is generally thought to be difficult to lose them to evaporation. However, when they are dispersed into air in small droplets during application in machining processes, their surface area becomes considerably higher. To determine the potential for metalworking fluids (MWF) filter losses, MWF mist was generated and collected on polyvinyl chloride (PVC) filters in test chamber. After collected MWF was exposed to clean air during designated period (range 10~240 minutes) and the filters were desiccated, losses were evaluated. As duration of clean air passing through PVC filter increased, loss of MWF gradually increased. MWF lost after 10 minutes ranged form 12.4 % to 21.8 % of the original loading mass, on average 53.3 % of the total loss. These results indicate that significant mass of MWF collected on PVC filters can be lost at the beginning of air sampling. Loss of MWF collected on PVC filter also occurred during desiccation without active airflow. In multiple regression to identify which factors influence the loss of MWF collected on PVC filter, both duration of air passing through PVC filter and MWF age (fresh vs. used) were significant predictor (p=0.0001). Therefore, workers' exposure to MWF measured method 0500, may underestimate true concentration. Further study is needed to develop a new method to quantify the workers' exposure to airborne MWF mist accurately.

• Analytical Science and Technology
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• v.27 no.4
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• pp.187-195
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• 2014

It is very important to minimize the damage of latent fingerprints at enhancing the contrast. This study proves the enhancement effects of cyanoacrylate-fumed latent fingerprints using p-dimethylaminobenzealdehyde (DMAB) on semi-porous surfaces and the influence factors. The latent fingerprints in experiment were developed for cyanoacrylate treatment in a vacuum chamber and used after drying at room temperature for 24 hours. For fluorescence staining, the cyanoacrylate-developed marks using DMAB were sublimated during 48 hours under the different conditions of surface area, temperature, atmospheric pressure. First experiment showed how surface area effects on the sublimation rate and fluorescence intensity by DMAB of particle size and container size. In addition, the fluorescence staining using DMAB with solvent-free contact method had the greatest fluorescence intensity after 36 hours and a low fluorescence intensity over a certain size of surface area. Second experiment showed that the evaporation of DMAB solid crystals got a satisfying result in a temperature of $20^{\circ}C$ and reduced time to get the greatest fluorescence intensity. It took a long time to get a optimum level of fluorescence intensity at $30^{\circ}C$ or more and it was less effective in fluorescence intensity. Third experiment on the pressure indicated that the fluorescence intensity of vacuum was weaker than nonvacuum but it was inapplicable to very high variations in pressure.

• Journal of the Korean Vacuum Society
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• v.15 no.3
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• pp.287-293
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• 2006

Diamond-like carbon (DLC) film was deposited using benzene $(C_6H_6)$ by r. f-plasma assisted chemical vapor deposition. The tribological properties of the DLC film were tested by rotating ball-on-disc type tribometer isolated by a chamber. The tribological test was performed in air environment of relative humidity ranging from 0 to 90% in order to observe the tribological behavior of the DLC film with the change of humidity. We used steel ball and DLC coated steel ball to investigate the effect of the counterface material. Using steel ball, the friction coefficient of DLC film increased from 0.025 to 0.2 as the humidity increased from 0% to 90%. In case of DLC coated steel ball which didn't form the Fe-rich debris, the friction coefficient showed much lower dependence of humidity as 0.08 in relative humidity 90%. We confirmed that the high humidity dependence of the friction coefficient using steel ball resulted from the increase of debris size with humidity and the formation of Fe-rich debris by the wear of steel ball. And the friction coefficient was immediately dropped when the relative humidity changed from 90% to 0% during test using steel ball. From this result, we confirmed that the effect of the Fe-rich debris on the friction coefficient was that Fe element in debris formed the highly sensitive graphitic transfer layer to humidity.