• Journal of Korean Society for Atmospheric Environment
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• 제22권E2호
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• pp.78-88
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• 2006

In order to study the characteristics of cloud, a real-scale experiment for cloud generation was carried out using an extinct vertical mine (430 m height) located in the northeastern Honshu, Japan. The dry particles generated from the three-step concentrations of NaCl solutions were used for cloud generation. The number size distributions of initial dry particles and cloud droplets were monitored by Scanning Mobility Particle Sizer (SMPS) and Forward Scattering Spectrometer Probe (FSSP) at bottom and upper sites of pit, respectively. The polymeric water absorbent film (PWAF) method was employed to measure liquid water content ($W_L$) as a function of droplet size. Moreover the chemical properties of individual droplet replicas were determined by micro-PIXE. The CCN number concentration shows the lognormal form in dependence of the particle size, while the number size distributions of droplets are bimodal showing the peaks around $9{\mu}m$ and $20{\mu}m$ for every case. In comparison to background mineral particles, right shifting of size distribution line for NaCl particles was occurred. When NaCl solutions with three-step different concentrations were neulized, $W_L$ shows the strong droplet size dependence. It varied from $10.0mg\;m^{-3}$ up to $13.6mg\;m^{-3}$ with average $11.6mg\;m^{-3}$. A good relationship between $W_L$ and cloud droplet number concentration was obtained. Both chemical inhomogeneities (mixed components with mineral and C1) and homogeneities (only mineral components or C1) in individual droplet replicas were obviously observed from micro-PIXE elemental images.

• Asian Journal of Atmospheric Environment
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• 제8권4호
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• pp.175-183
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• 2014

To visually and chemically verify the rainout of soot particles, a model experiment was carried out with the cylindrical chamber (0.2 m (D) and 4 m (H)) installing a cloud drop generator, a hydrotherometer, a particle counter, a drop collector, a diffusing drier, and an artificial soot particle distributer. The processes of the model experiment were as follows; generating artificial cloud droplets (major drop size : $12-14{\mu}m$) until supersaturation reach at 0.52%-nebulizing of soot particles (JIS Z 8901) with an average size of $0.5{\mu}m$-counting cloud condensation nuclei (CCN) particles and droplets by OPC and the fixation method (Ma et al., 2011; Carter and Hasegawa, 1975), respectively - collecting of individual cloud drops - observation of individual cloud drops by SEM - chemical identifying of residual particle in each individual droplet by SEM-EDX. After 10 minutes of the completion of soot particle inject, the number concentrations of PM of all sizes (> $0.3{\mu}m$) dramatically decreased. The time required to return to the initial conditions, i.e., the time needed to CCN activation for the fed soot particles was about 40 minutes for the PM sized from $0.3-2.0{\mu}m$. The EDX spectra of residual particles left at the center of individual droplet after evaporation suggest that the soot particles seeded into our experimental chamber obviously acted as CCN. The coexistence of soot and mineral particle in single droplet was probably due to the coalescence of droplets (i.e., two droplets embodying different particles (in here, soot and background mineral particles) were coalesced) or the particle capture by a droplet in our CCN chamber.

• 대한기계학회논문집
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• 제16권12호
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• pp.2376-2384
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• 1992

본 연구에서는 액적들의 분포상태가 비균일 분포 즉 비균일 액적크기 및 수밀 도 분포를 갖는 액적군에 대하여 집단점화 현상을 이론적인 해석을 통하여 규명한다. 이를 위하여 분사직후부터 점화순간까지의 과정 즉, 액적의 온도상승-증발-혼합기 형 성-반응의 진행-점화의 과정에 초기 액적들의 크기 및 수밀도 분포상태와 기체상의 조 건들이 중요 제변수들, 즉 온도, 속도, 성분질량농도 및 액적의 크기 분포등에 미치는 영향 등은 물론 액적군의 증발특성, 점화특성 등을 이론적 모델을 구성하여 해석한다. 결과들은 현재 사용되고 있는 집단연소 모델의 초기조건으로 사용하며, 액적들의 분포 상태에 따른 점화시의 액적군의 상태 및 점화 특성은 보다 향상된 연소시스템의 운전 및 설계에 분사조건으로서 활용될 것이 기대된다.

• 대기
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• 제28권2호
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• pp.211-222
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• 2018

Cloud droplet activation process is well described by $K{\ddot{o}}hler$ theory and several parameterizations based on $K{\ddot{o}}hler$ theory are used in a wide range of models to represent this process. Here, we test the two different method of calculating the solute effect in the $K{\ddot{o}}hler$ equation, i.e., osmotic coefficient method (OSM) and ${\kappa}-K{\ddot{o}}hler$ method (KK). To do that, each method is implemented in the cloud droplet activation parameterization module of WRF-CHEM (Weather Research and Forecasting model coupled with Chemistry) model. It is assumed that aerosols are composed of five major components (i.e., sulfate, organic matter, black carbon, mineral dust, and sea salt). Both methods calculate similar representative hygroscopicity parameter values of 0.2~0.3 over the land, and 0.6~0.7 over the ocean, which are close to estimated values in previous studies. Simulated precipitation, and meteorological variables (i.e., specific heat and temperature) show good agreement with reanalysis. Spatial patterns of precipitation and liquid water path from model results and satellite data show similarity in general, but on regional scale spatial patterns and intensity show some discrepancy. However, meteorological variables, precipitation, and liquid water path do not show significant differences between OSM and KK simulations. So we suggest that the relatively simple KK method can be a good alternative to the OSM method that requires various information of density, molecular weight and dissociation number of each individual species in calculating the solute effect.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.291-293
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• 2011

In this paper, the problem of transonic aerodynamic characteristics of a NACA0012 airfoil is numerically investigated in the inviscid gas-droplet two-phase flow with the compressible two-fluid model. In the present study, the airfoil flight in the cloud is simulated by taking account of the viscous drag of the droplets, the heat transfer, the phase change, and the droplet fragmentation The two-fluid equation system is solved by the fractional-step method and the WAF-HIL scheme. The effects of size and volume fraction of the droplets on the flow characteristics of the airfoil in the cloud are elaborated and discussed.

• Asian Journal of Atmospheric Environment
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• 제5권1호
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• pp.56-63
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• 2011

Quantifying the solute composition of a cloud droplet (or a whole droplet) is an important task for understanding formation processes and heating/cooling rates. In this study, a combination of droplet fixation and SR-XRF microprobe analysis was used to visualize and quantify elements in a micro-scale droplet. In this study, we report the preliminary outcome of this experiment. A spherical micro-scale droplet was successfully solidified through exposure to ${\alpha}$-cyano-acrylate vapor without affecting its size or shape. An X-ray microprobe system equipped at the beam line 37XU of Super Photon ring 8 GeV (SPring-8) was applied to visualize and quantify the elemental composition in an individual micro-scale droplet. It was possible to reconstruct 2D elemental maps for the K and Cl contained in a microdroplet that was dispensed from the 10-ppm KCl standard solution. Multi-elemental peaks corresponding to X-ray energy were also successfully resolved. Further experiments to determine quantitative measures of elemental mass in individual droplets and high-resolution X-ray microtomography (i.e., 3D elemental distribution) are planned for the future.

• Journal of Korean Society for Atmospheric Environment
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• 제24권E1호
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• pp.44-53
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• 2008

This study was undertaken to measure the properties of individual mineral particles in an artificially saturated atmosphere at a vertical extinct mine with 430 m height. By synchrotron radiation X-ray fluorescence (SR-XRF) microprobe analysis, it was possible to determine the elemental composition of residual insoluble particles on individual cloud droplet replicas formed on the Collodion film. The XRF visualized elemental maps enabled us not only to presume the chemical mixing state of particles retained in cloud droplet, but also to estimate their source. Details about the individual mineral particles captured by artificial cloud droplets should be helpful to understand about the removal characteristics of dust particles such as interaction with clouds. Nearly all individual particles captured in cloud droplets are strongly enriched in Fe. Mass of Fe is ranged between 41 fg and 360 fg with average 112 fg. There is a good agreement between single particle analysis by SR-XRF and bulk particle analysis by PIXE.

• 대한기계학회논문집
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• 제8권6호
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• pp.544-552
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• 1984

본 연구에서는 Chiu et al.의 집단연소이론에 대한 비정상집단연소모델(non- steady group combustion model)을 개발, 정지된 액적군에서 초기 액적들의 분포상태, 즉 초기액적들의 크기, 수밀도 및 액적군의 크기에 따른 연소시간, 연소형태 및 특성 과 화염의 성질등을 비정상 상태하에서 이론적인 모델을 통하여 고찰한다.

• 한국대기환경학회지
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• 제7권3호
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• pp.145-149
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• 1991

A one dimensiional cumulus cloud model has been developed for the investigation of temporal and altitudinal variation of trace gases and the wet deposition rates of sulfate for different simulation conditions. The results show that the dynamic field, liquid mixing ratios and the solubility of trace gases affect the distribution of trace gases and the droplet pH. Temporal variation of the predicted surface precipitation and sulfate deposition rates agree well with the field data.

• 한국대기환경학회지
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• 제6권2호
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• pp.176-182
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• 1990

A one dimensional cumulus cloud model has been developed to investigate the size distribution of hydrometeors at different heights and at different stages of cloud development. The model results show that the exponential distribution of droplet radius that was employed by many investigators can misinterpret the cloud dynamic fields during the life cycle of cumulus cloud. The results also show the bimodal distribution of cloud water mixing ratios at 25 $\mu$m and 645 $\mu$m in radius at 45 minutes of simulation time. The developed model can be applied in future on the parameterization of cloud microphysical processes and air pollution models.