• 설비공학논문집
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• 제10권5호
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• pp.610-618
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• 1998

In this study, a tracer gas technique was used to measure ventilation effectiveness in a thermal environmental chamber simulating an under-floor air conditioning system. A tracer gas of $SF_6$ was injected in a supply duct using step-up and step-down methods. Local mean ages and room mean ages were calculated from the measured concentrations under isothermal and cooling conditions with and without diffusers. Ventilation effectiveness is found to be higher in cooling ventilation operations than in isothermal operations. Results also show that ventilation effectiveness is not significantly affected by a diffuser.

• 한국지하수토양환경학회지:지하수토양환경
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• 제18권3호
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• pp.109-118
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• 2013

Characteristics of the transport of zero-valent iron nanoparticles (nZVI) in an aquifer were investigated to evaluate an application of nZVI-based reactive zone technology. Main flow direction of groundwater was north. Preferential flow paths of the groundwater identified by natural gradient tracer test were shown northeast and northwest. The highest groundwater velocity was $4.86{\times}10^{-5}$ m/s toward northwest. When the breakthrough curves obtained from the gravity injection of nZVI were compared with the tracer curves, the transport of nZVI was retarded and retardation factors were 1.17 and 1.34 at monitoring wells located on the northeast and northwest, respectively. The ratios of the amount of nZVI delivered to the amount of tracer delivered at the two wells mentioned above were 24 and 28 times greater than that of the well on the main flow direction, respectively. Attachment efficiency based on a filtration theory was $4.08{\times}10^{-2}$ along the northwest direction that was the main migration route of nZVI. Our results, compared to attachment efficiencies obtained in other studies, demonstrate that the mobility of nZVI was higher than that of results reported in previous studies, regardless of large iron particle sizes of the current study. Based on distribution of nZVI estimated by the attachment efficiency, it was found that nZVI present within 1.05 m from injection well could remove 99% of TCE within 6 months.

• Journal of Korean Society for Atmospheric Environment
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• 제23권E2호
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• pp.66-73
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• 2007

The introduction of tracer gas techniques to ventilation studies in indoor environments provides valuable information that used to be unattainable from conventional testing environments. Data acquisition systems (DASs) containing analogue-to-digital (A/D) converters are usually used to function the key role that records signals to storage in digital format. In the testing process, there exist a number of components in the measuring equipment which may produce system-based inference to the monitored results. These unwanted fluctuations may cause significant error in data analysis, especially when non-linear algorithms are involved. In this study, a pre-processor is developed and applied to separate the unwanted fluctuations (noise or interference) in raw measurements and to reduce the uncertainty in the measurement. Moving average, notch filter, FIR (Finite Impulse Response) filters, and IIR (Infinite Impulse Response) filters are designed and applied to collect the desired information from the raw measurements. Tracer gas concentrations are monitored during leakage and ventilation tests in the model test room. The signal analysis functions are introduced to carry out the digital signal processing (DSP) work. Overall the FIR filters process the $CO_2$ measurement properly for ventilation rate and mean age of air calculations. It is found that, the Kaiser filter was the most applicable digital filter for pre-processing the tracer gas measurements. Although the IIR filters help to reduce the random noise in the data, they cause considerable changes to the filtered data, which is not desirable.

• 한국산업보건학회지
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• 제16권3호
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• pp.290-301
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• 2006

A push pull hood system is frequently applied to control contaminants evaporated from an open surface tank. Efficiency of push pull hood system is affected by various parameters, such as, cross draft, vessel shapes, tank surface area, liquid temperature. A previous work assisted by flow visualization technique qualitatively showed that a strong cross draft blown from the pull hood to push slot could destroy a stable wall-jet on the surface of tank, resulting in the abrupt escape of smoke from the surface. In this study, the tracer gas method was applied to determine the effect of cross-draft on the capture efficiency qualitatively. A new concept of capture efficiency was introduced, that is, linear efficiency. This can be determined by measuring the mass of tracer gas in the duct of pull hood while the linear tracer source is in between push slot and pull hood. By traversing the linear tracer source from the push slot to the pull hood, it can be found where the contaminant is escaped from the tank. Total capture efficiency can be determined by averaging the linear efficiencies. Under the condition of cross-draft velocities of 0, 0.4, 0.75, 1.05 and 1.47m/s, total capture efficiencies were measured as 97.6, 95.4, 94.6, 92.7 and 70.5% respectively. The abrupt reduction of efficiency with cross-draft velocity of 1.47m/s was due to the destruction of tank surface wall-jet by the counter-current cross-draft. The same phenomenon was observed in the previous flow visualization study. As an alternative to overcome this abrupt efficiency drop, the 20% increase of hood flow rates was tested, resulting in 20% efficiency increase.

• 방사선산업학회지
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• 제2권3호
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• pp.135-140
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• 2008

A field tracer experiment using radioisotope was carried out to investigate the characteristics of a pollutant transport and a determination of the dispersion coefficients in a river system. The dispersion coefficients in the longitudinal and transverse directions were determined by using the measured concentration of a radioisotope. The two-dimensional numerical models were applied to calculate the flow and concentration fields at the experimental site. Several numerical simulations were performed to investigate the effects of the numerical results according to variations of the dispersion coefficients. The calculated concentrations agreed well with the measured ones.

• 대한토목학회논문집
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• 제26권2B호
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• pp.161-170
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• 2006

본 연구에서는 하천에서 오염물의 혼합 특성 연구를 위한 실험 방법으로서 방사성 동위 원소를 이용한 추적자 실험 방법을 제시하였다. 현장 실험시 추적자로서 방사성 동위원소를 사용할 경우 장점은 미량의 주입으로도 추적자의 감지가 용이하며 감지할 수 있는 범위 또한 넓다. 그리고 하상에 흡 탈착되는 추적자의 양이 비교적 작아 정확하면서 효율적으로 실험을 수행할 수 있다. 본 연구에서는 국내 자연하천 중 다양한 사행형태를 갖는 만곡구간을 선정하여 현장조사 및 추적자 실험을 7회 수행하였다. 실험에서 수집된 수리량 및 농도자료로부터 추적자의 2차원적 거동을 분석하고, 다양한 산정법을 통해 종횡 분산계수를 산출하였다. 그 결과 만곡이 심한 구간에서는 추적운의 중심이 만곡의 외측에 치우쳐 이동함을 확인하였고, 종분산계수 및 횡분산계수가 직선구간에 비해 증가함을 확인하였다.

• Ocean Science Journal
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• 제43권1호
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• pp.17-24
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• 2008

Over a period of 5 days between August 12 and 17, 2005, we performed a gas exchange experiment using the dual tracer method in a tidal coastal ocean located off the southern coast of Korea. The gas exchange rate was determined from temporal changes in the ratio of $^3He$ to $SF_6$ measured daily in the surface mixed layer. The measured gas exchange rate($k_{CO_2}$), normalized to a Schmidt number of 600 for $CO_2$ in fresh water at $20^{\circ}C$, was approximately $5.0\;cm\;h^{-1}$ at a mean wind speed of $3.9\;ms^{-1}$ during the study period. This value is significantly less than those obtained from floating chamber-based experiments performed previously in estuarine environments, but is similar in magnitude to values obtained using the dual tracer method in river and tidal coastal waters and values predicted on the basis of the relationship between the gas exchange rate and wind speed (Wanninkhof 1992), which is generally applicable to the open ocean. Our result is also consistent with the relationship of Raymond and Cole (2001), which was derived from experiments carried out in estuarine environments using $^{222}Rn$ and chlorofluorocarbons along with measurements undertaken in the Hudson River, Canada, using $SF_6$ and $^3He$. Our results indicate that tidal action in a microtidal region did not discernibly enhance the measured $k_{CO_2}$ value.

• 한국대기환경학회지
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• 제23권5호
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• pp.547-556
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• 2007

The release, sampling and analytical methods have been developed and tested for perfluorocarbons (PFCs) atmospheric tracers in order to gain insight into the atmospheric transport and dispersion over the urban conditions of Seoul, Korea. Although PFCs tracer experiments provide unique opportunities to test local and urban scale of transport and dispersion, no previous experiment with PFCs has been conducted in Korea. PMCH and PDCH were chosen as targeted tracers in our study due to their extreme low ambient concentrations and great sensitivities among various PFCs. For PFCs release system, a set of micro-metering pump, electronic balance, vaporizing furnace and high speed blower was constructed for precise and accurate release of tracers. The precision of released rate by this system was estimated to be 1%. Samplings of PFCs were carried out by fabricated portable air samplers with micro pumps and rotameters into glass tubes packed with 150 mg of Carboxen-569. The uncertainty of these sampling system was maintained below 14%. PMCH and PDCH were quantified in GC/ECD with preconditioned injection system to eliminate the interference compounds using traps and subsequent catalytic conversion system prior to column separation. Three intensive field test were undertaken during the springtime of 2002 to 2004 in eastern part of Seoul. Daily background samples were collected to characterize the background levels of PMCH and PDCH prior to their release. The observed background concentrations of PMCH ranged from 3.5 to 10.1 fL/L and varied randomly in location and time in this study. Its mean and standard variation of background concentration ($6.8{\pm}1.9\;fL/L$) are higher than those ($3.2{\sim}5.8\;fL/L$) of other historic tracer studies. Identified uncertainty for background PMCH was $1.7{\sim}2.0\;fL/L$ using this analytical system. Combined relative uncertainty in determining the tracer's concentrations was estimated as 17%. However, its background concentrations and uncertainty in concentration determination were found to be low and stable enough for tracer study.

• 한국지반공학회논문집
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• 제24권9호
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• pp.13-21
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• 2008

분배성 추적자 시험법은 LNAPLs(light nonaqueous phase liquids)로 오염된 지반을 조사하는데 아주 유용한 방법이다. 하지만 토양 내 유기물질로 흡착되는 분배성 추적자는 잠재적으로 분배성 추적자 시험법의 정확성에 영향을 끼칠 수 있다. 연구 결과, 추적자의 액상-LNAPL 간 분배 계수는 선형 관계를 보였다. 토양의 흠착능력을 평가하기 위해 흡착 등은 실험을 수행한 결과, Freundlich 흡착 등은 양상과 거의 일치하였고, 추적자의 흡착 정도는 토양 내 유기물질 함량이 증가함에 따라 증가하였다. 또한, 토양 유기물의 흡착능에 따른 잠재적 영향을 판단하고, 추적자 시험법에 의한 LNAPLs 예측의 오차를 수정하기 위해 서로 다른 유기물 함량을 가진 4개의 컬럼 실험을 수행하였다. 컬럼 실험 결과, 오염물질이 없더라도 주문진 표준사와 유기물질이 섞인 컬럼에서는 추적자의 분리 현상이 발생하였다. 오염물질로 케로진을 주입한 이후에 다시 추적자 시험법을 수행하여 파괴곡선을 구한 결과, 토양 유기물질에 대한 추적자의 흡착으로 인해 추적자의 지연계수(R)가 커졌고 LNAPLs의 오염도가 과대평가 되었다. 또한 컬럼 실험 결과를 바탕으로 유기물 함량과 LNAPLs의 예측도 사이의 관계식을 제안하였다.

• 한국대기환경학회지
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• 제34권2호
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• pp.259-268
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• 2018

The $PM_{2.5}$ samples were collected for every 6th day during one year at a suburban site in the Namwonsi, Jeollanamdo, Republic of Korea. Samples were analyzed for elemental carbon (EC), organic carbon (OC), and water-soluble organic carbon (WSOC), and levoglucosan. Although the water-soluble fraction of fine particulate OC consistently showed over a year, levoglucosan fraction of WSOC varied considerably from month to month. In this study, non-biomass-burning WSOC ($WSOC_{NBB}$) and biomass-burning $WSOC_{BB}$ were calculated with measurements of organic source tracer, levoglucosan, to better understand the temporal distribution and sources of WSOC. Two methods of predicting the secondary organic carbon from the biomass-burning $WSOC_{BB}$ Method and the EC-tracer Method were compared. Poor correlations between SOC estimated between two methods suggested that the use of the EC tracer method to estimate SOC may be significantly flawed. Direct measurements of levoglucosan and WSOC can provide a reasonable estimate of secondary organic carbon concentrations.