• Journal of Mechanical Science and Technology
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• 제16권12호
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• pp.1693-1701
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• 2002

The intermittent spray characteristics of a multi-hole and a single-hole diesel nozzle were experimentally investigated. The hole number of the multi-hole nozzle was 5, and the hole diameter of the 5-hole and the single-hole nozzle was the same as d$\_$n/=0.32 ㎜ with the constant hole length to diameter ratio(l$\_$n//d$\_$n/=2.81). The droplet diameters of the spray, including the time-resolved droplet diameter, SMD (Sauter mean diameter) and AMD (arithmetic mean diameter) , injected intermittently from the two nozzles into the still ambient were measured by using a 2-D PDPA (phase Doppler particle analyzer). Through the time-resolved evolutions of the droplet diameter, it was found that the structure of the multi-hole and the single-hole nozzle spray consisted of the three main parts : (a) the leading edge affected by surrounding air. and composed of small droplets; (b) the central part surrounded by the leading edge and mixing flow region and scarcely affected by the resistance of air, (c) the trailing edge formed by the passage of the central part. The SMD decreases gradually with the increase in the radial distance, and the constant value is obtained at the outer region of the radial distance (normalized by hole diameter) of 7-8 and 6 for the 5-hole and single-hole nozzle, respectively. The SMD along the centerline of the spray decrease shapely with the increase in the axial distance after showing the maximum value near the nozzle tip. The SMD remains the constant value near the axial distance(normalized by hole diameter) of 150 and 180 for the 5-hole and the single-hole nozzle, respectively.

• 의료ㆍ복지 건축 : 한국의료복지건축학회 논문집
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• 제28권4호
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• pp.89-97
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• 2022

Purpose: Because of the recent COVID-19 pandemic, there have been many cases of using portable negative pressure unit to convert general wards into temporary negative pressure isolation wards. The purpose of this study is to analyze the indoor environment of the switching type wards. Methods: Field measurements and experiments were conducted in a medical facility. Air volume, wind speed and pressure difference were measured in non-occupant state. Dispersion tests were performed with gas and particle matter. Results: The pressure difference between the wards and the corridor was higher than -2.5 Pa in normal situation. However, in the gas and particle dispersion tests, it was found that there were concerns about the spread through leakages in low-airtight walls or ceilings. In addition, it was confirmed that the pressure imbalance in ducts through the non-sealed diffusers could cause back flow during portable unit operation. Furthermore, when there was a pressure difference between adjacent wards planned to be at same pressure level, the possibility of the spread through the leakages was found. Implications: When using portable units for making switching type wards, it is necessary to create airtight space and seal the non-operation diffusers. In case of operating the air handling unit, T.A.B must be performed to adjust the duct balancing.

• 한국환경보건학회:학술대회논문집
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• 한국환경보건학회 2004년도 International Conference Global Environmental Problems and their Health Consequences
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• pp.193-196
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• 2004

To evaluate the acute effects of fine particles on pulmonary function, a longitudinal study was conducted. This study was carried out for the schoolchildren (3rd and 6th grades) living in Beijing, China. Children were asked to record their daily levels of peak expiratory flow rate using portable peak flow meter (mini-Wright) for 40 days. The relationship between daily PEFR and fine particle levels was analyzed using a mixed linear regression models including gender, height, the presence of respiratory symptoms, and daily average temperature and relative humidity as extraneous variables. The total number of students participating in this longitudinal study was 87. Daily measured PEFR was in the range of $253{\sim}501L/min$. On the daily basis, a PEFR measured in the morning was shown to be lower than that measured in the evening (or afternoon). The daily mean concentrations of $PM_{10}$ and $PM_{2.5}$ over the study period were $180.2\;{\mu}g/m^3$ and $103.2\;{\mu}g/m^3$, respectively. The IQR (inter-quartile range) of $PM_{10}$ and $PM_{2.5}$ were $91.8\;{\mu}g/m^3$ and $58.0\;{\mu}g/m^3$. Daily mean PEFR was regressed with the 24-hour average $PM_{10}$ (or $PM_{2.5}$) levels, weather information such as air temperature and relative humidity, and individual characteristics including gender, height, and respiratory symptoms. The analysis showed that the increase of fine particle concentrations was negatively associated with the variability in PEFR. The IQR increments of $PM_{10}$ or $PM_{2.5}$ (at 1-day time lag) were also shown to be related with 1.54L/min (95% Confidence intervals -2.14, -0.94) and 1.56L/min (95% CI -2.16, -0.95) decline in PEFR.

• 한국추진공학회지
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• 제15권4호
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• pp.26-34
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• 2011

스월러를 가진 천연가스 연료분사기가 장착된 희박 예혼합 연소기에서 화염구조의 일부분인 재순환 영역의 형성이 연소불안정에 미치는 영향에 대하여 실험적으로 연구를 진행하였다. PIV 계측기법으로 연소장에서의 화염의 안정화 그리고 불안정한 영역에서 유동장을 확인해본 결과 스월러에 의한 재순환 영역은 화염의 안정화 및 난류의 강도뿐만 아니라 재순환영역 형성의 크기에 따른 화염 재점화에도 영향을 미쳐 연소불안정 발생의 원인이 되는 열방출 섭동과 매우 밀접한 관계가 있음을 확인하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제36회 춘계학술대회논문집
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• pp.445-452
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• 2011

스월러를 가진 천연가스 연료분사기가 장착된 희박 예혼합 연소기에서 화염구조의 일부분인 재순환 영역의 형성이 연소불안정에 미치는 영향에 대하여 실험적으로 연구를 진행하였다. PIV 계측기법으로 연소장에서의 화염의 안정화 그리고 불안정한 영역에서 유동장을 확인해본 결과 스월러에 의한 재순환영역은 화염의 안정화 및 난류의 강도뿐만 아니라 재순환영혁 형성의 크기에 따른 화염 재점화에도 영향을 미쳐 연소불안정 발생의 원인이 되는 열방출 섭동과 매우 밀접한 관계가 있음을 확인하였다.

• 한국대기환경학회지
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• 제21권4호
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• pp.439-458
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• 2005

An automated analysis system for water soluble constituents in $PM_{2.5}$ has been developed. The system consists of a high capacity multi tube diffusion scrubber (MTDS), a low temperature particle impactor (LTPI), and two ion (anion and cation) chromatography (IC) systems. Atmospheric particles have been collected by passing sample air through a thermostated MTDS followed by a LTPI. This system allows simultaneous measurements of soluble ions in $PM_{2.5}$ at 30 minutes interval. At the air sampling flow rate of 1.0L/min, the detection limits of the overall system are in the order of tens of $ng/m^3$. This system has been successfully used for the measurement of particulate components of Seoul air from April 2003 to January 2004. $SO_4^{2-},\;NO_3^-,\;NH_4^+,\;NO_2^-,\;Cl^-,\;Na^+,\;K^+,\;Ca^{2+},\;and\;Mg^{2+}$ are the major ionic species for $PM_{2.5}$ at Seoul. Among them, $SO_4^{2-},\;NO_3^-\;and\;NH_4^+$ are the most abundant ions, contributed up to $86\%$ of the total and the concentrations were higher than those in any other urban sites in the world except for Chinese cities. There are high pollutant episodes which contribute about $15\~20\%$ of annual average values of the major ions. During the episode, the all parcels were transported from the asian continent and $PM_{2.5}$ were significantly neutralized. This suggests that aged and long range transported pollutants caused the high pollutant episodes. They showed a distinct daily and seasonal variations:they showed a peak in the early morning caused by the night-time accumulation of particulate matters. Atmospheric reactions including gas-to-particle reactions and inter-particle reactions and meteorological parameters including relative humidity and ambient temperature were described with related to the $PM_{2.5}$ 5 concentrations. All of the ionic species showed higher concentrations during the spring than those for summer and winter.

• 한국대기환경학회지
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• 제29권5호
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• pp.553-573
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• 2013

This paper aims to give a summary and review of the research trend about subjects of Asian Dust (AD) storm in the last three decades. The AD research was focused on classification of synoptic scale data and finding inflow pathway in early stage. Recently, new approaches have been made to explain chemical composition, transportation, transboundary movement reaction of AD, using satellite data, 3D modeling, the aerosol time of flight mass spectroscopy, etc. During AD events, a large amount of dust particles flow into Korea and Japan from AD source areas, and they are highly likely to be mixed with toxic substances when air mass contained AD particles pass over seriously polluted areas. We concluded that, considering that AD events were classified into two cases according to the source area and pathway, the concentrations of crustal components did not increase at the initial stage of AD events, Whereas ammonium-sulfate, trace metal element, OC, EC relatively increased in the early stage. This explains AD events have the possibility of being accompanied with polluted air mass or particles. Also, we further need to compare and summarize the results of AD studies which already have been conducted, and prepare strategies for particle management, particularly for Black Carbon (BC) and Brown Carbon (BrC) which are considered to induce climate change effects.

• Asian Journal of Atmospheric Environment
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• 제5권1호
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• pp.21-28
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• 2011

Occupational nanomaterial exposure is an important issue in the manufacture of such products. People are also exposed to various nanoparticles in their living environments. In this study, we investigated nanoparticle formation during the reaction of ozone and volatile organic compounds (VOCs) emitted from a commercial air freshener, one of many widely used consumer products, in a $1-m^3$ reaction chamber. The air freshener contained various VOCs, particularly terpenes. A petri dish containing 0.5 mL of the air freshener specimen was placed in the bottom of the chamber, and ozone was continuously injected into the center of the chamber at a flow rate of 4 L/min with an ozone concentration of either 50, 100 or 200 ppb. Each test was conducted over a period of about 4 h. The higher ozone concentrations produced larger secondary nanoparticles at a faster rate. The amount of ozone reacted was highly correlated with the amount of aerosol formation. Ratios of reacted ozone concentration and of formed particle mass concentration for the three injected ozone concentrations of 50, 100 and 200 ppb were similar to one other; 4.6 : 1.9 : 1.0 and 4.7 : 2.2 : 1.0 for ozone and aerosol mass, respectively.

• 한국결정성장학회지
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• 제26권1호
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• pp.41-48
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• 2016

현재 비철제련분야에서의 제련후 폐기물은 약 200만톤 이상으로 추산되고 있다. 현재까지는 비철금속을 추출하는 연구가 주를 이루고 있으며, 금속 추출 후 슬래그의 활용에 대한 연구는 미비한 상황이다. 이에 본 연구에서는 동제련 분야에서 발생된 슬래그를 콘크리트용 골재로 사용하기 위해 동제련 슬래그의 입도분포와 잔골재로 사용된 강사의 대체 치환율 변화를 실험인자로 선정하여, 굳지 않은 모르타르의 특성을 평가하였다. 실험결과, 동제련 슬래그의 입도분포에 따라 플로우, 공기량 및 건조수축의 변화를 참조하여 동제련 슬래그의 적정입도분포를 산정하는 것이 중요함을 확인하였으며, 동제련 슬래그를 잔골재로 치환함으로 인해 응결 및 단위용적질량은 증가하는 것으로 확인되었다. 또한 강사와 유사한 입도분포를 갖는 동제련 슬래그를 사용하였을 경우에는 강사를 사용한 경우보다 슬럼프, 공기량, 응결 및 건조수축, 단위용적 질량이 증가하는 것으로 나타났다. 따라서, 동제련 슬래그를 콘크리트용으로 사용하기 위해서는 적정 입도분포와 치환율이 산정되어야 할 것으로 판단된다.

• 한국수자원학회논문집
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• 제55권10호
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• pp.761-774
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• 2022

가뭄과 홍수의 예측, 기후변화가 유역 유출량, 더 나아가 수질 및 생태계에 미치는 영향의 정확한 분석을 위해서는 수문 모의 과정의 불확실성을 정량화하고 최소화하기 위한 노력이 필요하다. 수문자료동화는 수문모형의 상태량이나 매개변수를 갱신(update)하여 모의 초기 조건의 가장 가능성 있는 추정치를 생성하는 기법으로, 실시간 관측 정보를 이용하여 예측 정확도를 향상시킬 수 있는 방법이다. 본 연구에서는 airGRdatassim 모형을 이용하여 앙상블 기반 순차 자료동화 기법인 앙상블 칼만 필터와 파티클 필터로 용담댐 유역에 대해 일 유출을 모의하고, 자료동화 기법별 특성을 비교 및 분석하였다. 모의 결과, Kling-Gupta efficiency (KGE) 지표가 자료동화 적용 전 0.799에서 앙상블 칼만 필터와 파티클 필터 적용시 각각 0.826, 0.933으로 향상되었다. 또한 기상 강제력 노이즈의 범위, 갱신 대상 상태량 설정, 앙상블 수 등 수문자료동화의 설정과 관련된 하이퍼-매개변수(hyper-parameter)의 불확실성이 모의 예측 성능에 미치는 영향을 분석하였다. 강수 및 잠재 증발산 강제력의 오차 범위에 대한 민감도 분석 결과, 모든 모의 범위에서 파티클 필터가 앙상블 칼만 필터보다 예측 성능이 우수하였다. 파티클 필터는 기상 강제력 오차 크기가 작을수록 모의 성능이 향상되었으며, 앙상블 칼만 필터는 상대적으로 오차가 큰 경우 최적 성능이 확인되었다. 한편, 자료동화시 갱신되는 상태량의 종류를 줄일수록 자료동화에 의한 모의 성능은 감소하였다. 본 연구의 모의 실험 결과는 앙상블 자료동화를 이용하여 일 유출 모의 정확도 향상이 가능하지만, 최적 성능을 발휘하기 위해서는 수문자료동화 기법별 하이퍼-매개변수의 적정한 조정이 필요함을 함의한다.