• Journal of Environmental Impact Assessment
• /
• v.11 no.3
• /
• pp.173-187
• /
• 2002

토양 속에서 발생될 수 있는 용질과 용매의 복합 수송시스템을 대상으로 한 연구 중 회석상태로부터 포화상태에 이르기까지의 넓은 농도분포를 가지는 토양 용액에 적용될 수 있는 물리 화학적 이론에 입각한 지배방정식을 발표한 연구는 전무한 실정이다. 본 연구는 용매와 토양기체간 그리고 용질과 결정간의 상변화를 고려한 연립물질수지방정식을 제시하고, 여기에 타율적 대류를 포함하는 상호확산 분산수송방정식을 도입하여 대류와 확산에 관한 프럭스를 분리, 결정하는 것을 목적으로 한다. 대류 플럭스의 결정은 타율적으로 이루어지는 것이 이론적으로 타당하며, 이러한 타율적 대류 플럭스가 제공된다면 본 연구에서 제시된 지배방정식을 이용해서 토양용액의 복합수송 시스템을 범용적으로 해석, 예측할 수 있을 것으로 판단된다.

• Journal of computational fluids engineering
• /
• v.11 no.1 s.32
• /
• pp.36-42
• /
• 2006

The existing numerical approximations of convection flux, especially the spatial higher-order difference schemes, in unstructured cell-centered finite volume methods are examined in detail with each other and evaluated with respect to the accuracy through their application to a 2-D benchmark problem. Six higher-order schemes are examined, which include two second-order upwind schemes, two central difference schemes and two hybrid schemes. It is found that the 2nd-order upwind scheme by Mathur and Murthy(1997) and the central difference scheme by Demirdzic and Muzaferija(1995) have more accurate prediction performance than the other higher-order schemes used in unstructured cell-centered finite volume methods.

• Membrane Journal
• /
• v.21 no.1
• /
• pp.84-90
• /
• 2011

We studied the effects of induction of natural convection instability flow (NCIF) according to the gravitational orientation (inclined angle) of the membrane cell on the reduction of membrane fouling in ultrafiltration (UF) of colloidal silica solutions. Five colloidal silica solutions with different silica size (average size = 7, 12, 22, 50 and 78 nm) were used as UF test solutions. The silica particles in colloidal solutions form cakes on the membrane surface thereby causing severe reduction in the flux. The UF performance according to the gravitational orientation of the membrane cell (from 0 to $180^{\circ}$ inclined angle), was examined in an unstirred dead-end cell. We evaluate the effects of NCIF on membrane performance as the flux enhancement ($E_i$). In the dead-end UF of smaller size (7, 12 and 22 nm) silica colloidal solutions, changing the gravitational orientation (inclined angle) of the membrane cell induces NCIF in the membrane module and higher inclined angle and smaller size silica colloidal solution offer more stronger NCIF. This induced NCIF enhances back transport of the deposited silica solutes away from the membrane surface, therefore gives for the improvement of permeate flux. But in UF of more larger size (50 and 78 nm) silica colloidal solutions, NCIF effects are not appearing. These results suggest that the size of colloidal particle affects the extent of NCIF occurrence.

• Proceedings of the Membrane Society of Korea Conference
• /
• 1996.04a
• /
• pp.46-47
• /
• 1996

막분리 공정의 공업적인 이용을 위해서는 막을 특정 용기에 적재한 모듈의 형태가 요구되는데 모듈의 형태에 따라 평판형(plate and frame), 나권형(spiral wound), 관형(tubular), 중공사형(hollow fiber)모듈 등이 있다. 이 중에서 관형 시스템은 내경이 12.5~25 mm, 길이 0.6~6.4 m에 이르는 비교적 큰 open channel로 되어 있으며 공급액 유로가 일반적으로 커서 전처리를 행하지 않고도 fouling이 적으며, 또한 막 표면의 세정이 약품에 의한 것 이외에 스폰지 볼 등에 의한 물리적 세정도 가능하므로 응용 범위가 넓다는 것이 특징이다. 한외여과 공정의 가장 큰 문제점은 농도분극 및 fouling 현상에 의한 플럭스 감소이다. 농도분극 현상은 경계층에서 용질의 대류,확산적인 전달에 기인하여 막 표면으로 갈수록 진해지는 용액층의 형성을 의미한다. 이 현상은 가역적인 과정으로서 감압함으로 원상태로 회복이 가능하며 조작 압력에서 정상상태가 되면 막투과 플럭스는 일정한 값을 유지한다.

• Membrane Journal
• /
• v.22 no.5
• /
• pp.332-341
• /
• 2012

We studied the effects of induction of natural convection instability flow (NCIF) according to the gravitational orientation (inclined angle) of the membrane cell on the reduction of membrane fouling in the constant-flow ultrafiltration (UF) of colloidal silica solutions. Five colloidal silica solutions with different silica size (average size = 7, 12, 22, 50 nm and 78 nm) were used as UF test solutions. The silica particles in colloidal solutions form cakes on the membrane surface thereby causing severe membrane fouling. The constant-flow UF performance according to the gravitational orientation of the membrane cell (from $0^{\circ}$ to $180^{\circ}$ inclined angle), was examined in an unstirred dead-end cell. We evaluate the effects of NCIF on the suppression of fouling formation by measuring the variation of transmembrane pressure (TMP) and the increase of critical flux by using the flux-stepping method. In the constant-flow dead-end UF for the smaller size (7, 12 nm and 22 nm) silica colloidal solutions, changing the gravitational orientation (inclined angle) of the membrane cell above the $30^{\circ}$ angle induces NCIF in the membrane module. This induced NCIF enhances back transport of the deposited silica solutes away from the membrane surface, therefore gives for the reduction of TMP. But in the constant-flow UF for the more larger size (50 nm and 78 nm) silica colloidal solutions, NCIF effects are not appearing. The critical flux is increased as increasing the module angle and decreasing the silica size. Those results show that the intesity of NCIF occurrence in membrane module is more higher as increasing the module angle and decreasing the silica size.

• Membrane Journal
• /
• v.29 no.1
• /
• pp.18-29
• /
• 2019

The dead-end ultrafiltration (UF) of BSA protein solution was performed to investigate the defouling effects of natural convection instability flow (NCIF) induced in membrane module. The permeate fluxes were measured according to the inclined angles ($0{\sim}180^{\circ}$) of membrane module with respect to gravity, and analyzed using the blocking filtration model. NCIF are more induced as the inclined angles increased from $0^{\circ}$ to $180^{\circ}$, and the induced NCIF enhances flux. Comparing the fluxes at $0^{\circ}$ inclined angle (no NCIF induction) and $180^{\circ}$ (maximum NCIF induction), the flux enhancements by NCIF induction are increased about 5 times in the short-term UF operation (2 hours) and about 17 times in the long-term operation (20 hours). As applying the blocking filtration model, it is more suitable to analyze the flux results by using the intermediate blocking model in the early times of UF operation within 15 minutes and then thereafter times by using the cake filtration model. NCIF induced at $180^{\circ}$ inclined angle reduces the intermediate blocking fouling at about 67% in the early times operation and thereafter the cake layer fouling at about 99.9%. The main defouling mechanism of NCIF induced in the membrane module is suppress the formation of protein cake layer.

• Membrane Journal
• /
• v.29 no.3
• /
• pp.147-154
• /
• 2019

The permeate flux increments of a natural convection instability flow (NCIF) caused by the change of inclined angles ($0{\sim}180^{\circ}$) to gravity of the commercial membrane module were tested in the dead-end membrane filtration of BSA protein solution. The NCIF are more generated as the inclined angle increased from $0^{\circ}$ to $180^{\circ}$, and the occurred NCIF enhances permeate flux. However, the commercial module can only generate NCIF by completely removing the air gap in module. Since the custom design module designed in this study is permeated in a crossward direction ($90^{\circ}$), NCIF is always generated even if there is the air gap in module. The results of membrane filtration of BSA and dextran solutions using a custom design module showed that the flux in the crossward direction is increased to about 3.8 times for BSA solution and 1.8 times for dextran solution after two hours of operation due to the occurrence of NCIF. Also, NCIF generation is continued during 20 hours filtration of BSA solution, increasing the permeate flux to about 7.5 times. Since the custom design module with a permeation in the crossward direction and NCIF is always generated within the module, so it is possible to expect an increase in permeate flux due to the suppression of fouling formation, and thus to be utilized as a superb dead-end membrane module.

• Korean Journal of Agricultural and Forest Meteorology
• /
• v.5 no.2
• /
• pp.138-149
• /
• 2003

Korean regional network of tower flux sites, KoFlux, has been initiated to better understand $CO_2$, water and energy exchange between ecosystems and the atmosphere, and to contribute to regional, continental, and global observation networks such as FLUXNET and CEOP. Due to heterogeneous surface characteristics, most of KoFlux towers are located in non-ideal sites. In order to quantify carbon and energy exchange and to scale them up from plot scales to a region scale, applications of various methods combining measurement and modeling are needed. In an attempt to infer regional-scale flux, four methods (i.e., tower flux, convective boundary layer (CBL) budget method, MM5 mesoscale model, and NCAR/NCEP reanalysis data) were employed to estimate sensible heat flux representing different surface areas. Our preliminary results showed that (1) sensible heat flux from the tower in Haenam farmland revealed heterogeneous surface characteristics of the site; (2) sensible heat flux from CBL method was sensitive to the estimation of advection; and (3) MM5 mesoscale model produced regional fluxes that were comparable to tower fluxes. In view of the spatial heterogeneity of the site and inherent differences in spatial scale between the methods, however, the spatial representativeness of tower flux need to be quantified based on footprint climatology, geographic information system, and the patch scale analysis of satellite images of the study site.

• Membrane Journal
• /
• v.29 no.6
• /
• pp.329-338
• /
• 2019

The constant-pressure and constant-flux membrane filtration experiments of alumina colloidal solution are performed to investigate defouling effect of the natural convection instability flow (NCIF) induced in membrane module. The permeate flux at constant-pressure and the transmembrane pressure (TMP) at constant-flux experiments are measured by changes the inclined angle (0, 90 and 180°) of membrane module to the gravity, and flux results are analyzed by using the blocking filtration model. NCIF are more induced as the inclined angles increased from 0° to 180°, and the maximum induced NCIF at 180° angle enhances flux to 2.8 times and reduces TMP to 85% after two-hour operation. As a result of analyzing flux data by applying the blocking filtration model, it is more reasonable to analyze them by using the intermediate blocking model within 15-minute operation time and then thereafter times by using the cake filtration model. The induced NCIF at 180° angle reduces the intermediate blocking fouling at 52% in the early operation time of 15-minute and thereafter the cake layer fouling at 93%. The main membrane fouling control mechanism of NCIF induced in membrane module is evaluated as suppressing the formation of the cake layer of particulate colloidal materials on membrane surface.

• Journal of the Korean earth science society
• /
• v.35 no.1
• /
• pp.41-53
• /
• 2014

The special observation using Radiosonde was performed to investigate precipitation events over the east coast of Korea during the winter season from 5 January to 29 February 2012. This analysis focused on the various indices to describe the characteristics of the atmospheric instability. Equivalent Potential Temperature (EPT) from surface (1000 hPa) to middle level (near 750 hPa) was increased when the precipitation occurred and these levels (1000~750 hPa) had moisture enough to cause the instability of atmosphere. The temporal evolution of Convective Available Potential Energy (CAPE) appeared to be enhanced when the precipitation fell. Similar behavior was also observed for the temporal evolution of Storm Relative Helicity (SRH), indicating that it had a higher value during the precipitation events. To understand a detailed structure of atmospheric condition for the formation of precipitation, the surface remote sensing data and Automatic Weather System (AWS) data were analyzed. We calculated the Total Precipitable Water FLUX (TPWFLUX) using TPW and wind vector. TPWFLUX and precipitation amount showed a statistically significant relationship in the north easterly winds. The result suggested that understanding of the dynamical processes such as wind direction be important to comprehend precipitation phenomenon in the east coast of Korea.