• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.2 s.233
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• pp.239-246
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• 2005

Effects of subcooling on pool boiling heat transfer in vertical annuli with closed bottoms have been investigated experimentally. For the test, a tube of 19.1mm diameter and the water at atmospheric pressure have been used. Three annular gaps of 7.05, 18.15, and 28.20 have been tested in the subcooled water and results of the annuli are compared with the data of a single unrestricted tube. The increase in pool subcooling results in much change in heat transfer coefficients. At highly subcooled regions, heat transfer coefficients for the annuli are much larger than those of a single tube. As the heat flux increases and subcooling decrease, a deterioration of heat transfer coefficients is observed at the annulus of 7.05mm gap. Single-phase natural convection and liquid agitation are the governing mechanisms for the single tube while liquid agitation and bubble coalescence are the major factors at the bottom closed annuli.

• Advances in aircraft and spacecraft science
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• v.2 no.2
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• pp.183-198
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• 2015

Scramjets are a class of hypersonic airbreathing engine that are associated with realizing the technology required for economical, reliable access-to-space and high-speed atmospheric transport. After-burning augments the thrust produced by the scramjet nozzle and creates a more robust nozzle design. This paper presents a numerical study of three parameters and the effect that they have on thrust augmentation. These parameters include the injection pressure, injection angle and streamwise injection position. It is shown that significant levels of thrust augmentation are produced based upon contributions from increased pressure, mass flow and energy in the nozzle. Further understanding of the phenomenon by which thrust augmentation is being produced is provided in the form of a force contribution breakdown, analysis of the nozzle flowfields and finally the analysis of the surface pressure and shear stress distributions acting upon the nozzle wall.

• Journal of ILASS-Korea
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• v.9 no.3
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• pp.29-34
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• 2004

To investigate characteristics and micro-explosion of single-droplets of emulsified fuel, water is mixed with diesel oil by using ultrasonic energy fuel feeding system. The fuel characteristics is analysed through H-NMR spectrum and micro-explosion phenomena of the emulsified fuel is also investigated. The life times of droplets of conventional diesel fuel, ultrasonic energy added diesel fuel and emulsified fuel we obtained additionally. According to this study, the micro-explosion phenomena of single-droplets happen in atmospheric pressure condition, a curve form of emulsified fuel's life tim is different from diesel fuel's one and the change of chemical structures is a cause of ultrasonic-energy-added diesel fuel effect.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.337-342
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• 1996

The pool-boiling critical heat flux (CHF) of water on small flat plates has been experimentally investigated focusing on the effects of the inclination angle and size of the heated surface under near atmospheric pressure. The second-phase experiment was accomplished to find out the general CHF behavior for over-all inclination angles from -90$^{\circ}$ to 90$^{\circ}$using two plate-type test sections (30$\times$150 mm and 40$\times$150 mm) submerged in a slightly subcooled water pool. Test results generally confirm the first-phase findings and show little effect of inclination angle for inclined upward-facing cases. CHF position moves to lower position with the increase of the heater characteristic size and inclination angle(from -30$^{\circ}$to 60$^{\circ}$).

• Journal of the Korean Ceramic Society
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• v.23 no.1
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• pp.1-6
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• 1986

The shrinkage rate of solid state sintering has been theoretically derived by combining the rate equation of material transport and the net free energy change resulting from the decrease of solid-vapor interface and the increase of grain boundary during sintering. For a sinteing model an idealized situation of the spherical particles with BCC packing was taken as the initial condition and the shrinkage was assumed to occur by forming the flat circualr grain boundaries on each particle. The plotted shrinkage rates as a function of grain boundary to surface energy ratio $(gamma_g/gamma_s)$ have shown that the relative density increases linearly at the initial stage of sintering but the shrinkage rate is decreased upon further sintering due to a decrease in driving force for densificaton. It has been also shown that the densification is critically affected by the $gamma_g/gamma_s$ ratio. In order to get the complete densificatin the ratio should be less than $sqrt{3}$. Any additive or atmospheric condition causing the decrease of$_g/gamma_s$ ratio will enhance sintering.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.47 no.2
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• pp.154-159
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• 2014

The increasing of atmospheric $CO_2$ are changing the pH (ocean acidification) and temperature of the sea. Although the effects of ocean acidification on calcifying organisms have well-documented, only a few studies have examined the combined effects of ocean acidification and elevated temperature. This study investigated the effects of ocean acidification and elevated temperature for 2100 on survival and growth of juvenile abalone, Haliotis discus hannai. Ocean acidification was simulated by bubbling $CO_2$ into seawater at concentrations of 1,000 and 1,500 ppm, and temperature was set at room temperature $+2^{\circ}C$. Neither $CO_2$ nor temperature had a significant effect on survival of abalone, while both significantly affected growth. There was no significant interaction between the two factors. Shell length can be used as a growth index of abalone to access the impacts of ocean acidification and elevated temperature.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2000.11a
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• pp.263-264
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• 2000

여과포 표면상에 도달하는 입자의 농토를 낮추거나 균일하게 유지시킬 경우, 부착된 입자층 두께의 성장으로 인한 압력손실의 증가율을 줄일 수 있고 이로 인하여 탈진 주기 또한 감소시킬 수 있다. 탈진조작의 저감으로 인하여 여과포의 수명 증대로 여과포의 교체 시기를 연장시킬 수 있으므로 여과포 집진장치의 운전 및 유지 보수비의 저감을 이룰 수 있다. 본 연구에서는 집진용기의 중간부분에 위치한 접선 유입관을 통하여 오염입자를 함유한 기체유동을 유입시킨 후, 원심력과 난류확산에 의하여 집진용기 내벽과 내통(inner tube) 벽면에 부착된 입자는 중력에 의하여 용기 바닥으로 모인 후 바닥면에 설치된 스크래퍼(scraper)를 통하여 분리 처리될 수 있는 새로운 형상의 집진장치를 개발하고자 하였다. (중략)

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2000.11a
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• pp.287-288
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• 2000

환경성 질환은 본래 그 특성상 특이한 증상, 징후를 보이지 않고 일반적인 건강 이상상태를 보이는 것을 특징으로 하기 때문에 대기오염이 인체에 미치는 영향에 대한 생리학적 기전은 아직 완전히 밝혀지지 않았으며 개인수준의 건강영향을 정확히 파악하기란 매우 어려우므로 사망자료나 의료보험자료와 같은 인구집단의 건강관련자료를 이용하는 역학연구가 필수적이다. (중략)

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2003.11a
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• pp.421-424
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• 2003

서울지하철은 총연장 286.9km에 1일 4226회의 운행회수 그리고 대중교통수단 중 총 34.1％의 최다 수송분담율을 담당하고 있다. 서울시의 도심교통문제 해결 방안으로 시민들에게 대중교통 이용을 적극적으로 권장하고 있으나, 지하철 역사의 환경문제는 답보 상태를 유지하고 있는 것이 현실이다. 지하철내의 먼지문제는 이미 심각한 사회문제로 대두된 지 오래이며 이를 개선하기 위하여 지하철공사와 도시철도공사에서는 환기시스템의 개선, 환기 및 공기정화시설의 설치 그리고 잦은 물청소실시 등을 시행하여 오고 있어 그간 상당한 효과를 이룬 것도 사실이다. (중략)

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2003.11a
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• pp.143-144
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• 2003

최근 들어 플라즈마 촉매 복합공정을 이용하여 NOx를 제거시키기 위한 연구가 활발히 이루어지고 있다. 저온 플라즈마 공정중 하나인 DBD (Dielectric barrier discharge) 공정 내에서 NO는 NO$_2$로 매우 효과적으로 전환된다. 촉매공정의 경우 NO보다 NO$_2$가 주입되는 경우 NOx 제거 효율이 높고 촉매의 피독 현상도 줄어들게 된다. 따라서 DBD를 이용하여 NO의 전환율을 높일 수 있다면 플라즈마 촉매 복합공정의 NOx 제거 효율은 매우 높아진다. DBD 반응기 내에서 NO를 NO2로 전환시키는데 가장 중요한 역할을 하는 것 중 하나는 오존 (O$_3$)이다. (중략)