Potential impact of pore-scale incomplete mixing on biodegradation in aquifers: From batch experiment to field-scale modeling

Kang, Peter K.,Bresciani, Etienne,An, Seongnam,Lee, Seunghak Elsevier 2019 ADVANCES IN WATER RESOURCES Vol.123 No.-

<P><B>Abstract</B></P> <P>Biogeochemical reactions take place when reactants are present at the same location and time, which occurs through pore-scale mixing. Although the degree of mixing should be variable in space and time, most conventional reactive transport models do not consider mixing-dependent reaction rates and often make predictions based on rates measured with batch experiments. We quantify the effect of pore-scale mixing on the biodegradation rate of dissolved organic carbon (DOC) with sediment batch experiments, and study its potential impact on the field-scale fate and transport of DOC with numerical simulations. We collected sediment samples from an aquifer storage transfer and recovery (ASTR) field site located in Busan, South Korea, and conducted batch experiments to measure mixing-dependent biodegradation rates. Complete mixing conditions were realized by continuously shaking the batch, and diffusion-limited mixing conditions were realized by keeping the batch under static conditions. The two mixing conditions are most widely used conditions in batch experiments and they also represent the maximum and minimum degree of mixing. The different mixing conditions led to significant differences in the biodegradation rates (a factor of 4.9 on average). We then performed reactive transport modeling using the measured biodegradation rates to study the potential impact of pore-scale incomplete mixing on the field-scale DOC biodegradation. The results show that pore-scale mixing can significantly affect the effectiveness of biodegradation at the ASTR site. We generalize this finding by performing a comprehensive nondimensional sensitivity analysis of the fate and transport of DOC to pore-scale mixing conditions over a wide range of P e ´ clet and Damköhler numbers. We show that pore-scale incomplete mixing can be a major source of uncertainty in field-scale model predictions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Sediment batch experiments show mixing-dependent DOC biodegradation rates. </LI> <LI> Pore-scale incomplete mixing has significant potential impact on field-scale DOC biodegradation. </LI> <LI> Pore-scale incomplete mixing can be a major source of uncertainty over a wide range of Pe and Da numbers. </LI> </UL> </P>

Novel evaluation method for the continuous mixing process of bimodal particles

Park, Chanho,Kim, Junghwan,Landon, Robert S.,Lyu, Byeonggil,Cho, Hyungtae,Moon, Il Elsevier Sequoia 2019 Powder technology Vol.344 No.-

<P><B>Abstract</B></P> <P>The continuous mixing process of powder is used in many industries. Careful evaluation of the degree of the mixing is essential to enhance equipment performance. However, no single evaluation method has been universally adopted for the continuous mixing process of bimodal particles due the methods' poor applicability across multiple process concepts. Presented here are two indices to evaluate mixing in the transverse and axial directions. In this study, the indices are estimated at steady state based on Variance among Bimodal Bin Counts (VBBC), which was introduced as an evaluation method of a bimodal particle mixing system in our previous study. The VBBC mixing index for a continuous mixer is introduced to evaluate the transverse mixing of particles, while an axial stability factor is introduced to evaluate the mixing in the axial direction, which is indicative of the consistency of the process. The importance of each index depends on the characteristics of the process. Therefore, several strategies are suggested for applying the methods to practical cases. In addition, a hypothetical example is presented to illustrate their application: five continuous mixers having differently angled blades are assumed because the blade angle is the most easily modifiable design factor. The bimodal particle mixing processes are simulated using the Discrete Element Method (DEM). Based on the application example, both indices are calculated and the optimal design of a screw is suggested.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Novel method is developed to evaluate the continuous powder mixing process. </LI> <LI> Variance among Bimodal Bin Counts is adopted for the novel method. </LI> <LI> The method includes two indices to evaluate the transverse and the axial mixing. </LI> <LI> Several strategies are introduced to apply the method to practical systems. </LI> <LI> Five continuous powder mixers are simulated with DEM and evaluated with the method. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Impact of Mixing Methods and Cement Dosage on Unconfined Compressive Strength of Cement-Stabilized Macadam

Kaiyin Zhao,Lijun Zhao,Jinru Hou,Zhongxu Feng,Wenzhi Jiang 한국콘크리트학회 2022 International Journal of Concrete Structures and M Vol.16 No.3

The technology of vibratory mixing has been applied to improve the compressive strength of cement-stabilized macadam (CSM). The aim of this study is to investigate the effect of vibration acceleration and cement dosage on the unconfined compressive strength and density of CSM. The mixtures with four cement dosages (2%, 3%, 4%, and 5%) were prepared by conventional mixing (0 g) and vibratory mixing (1 g, 2 g, and 3.5 g). The unconfined compressive strength was tested under different mixing methods. And the microstructure of CSM was analyzed by scanning electron microscope. The results indicate that samples using vibratory mixing have higher strengths, lower coefficient of variation, and denser microstructures, compared with the conventional compulsory mixing. Compared with 15% in conventional mixing, the strength variable coefficient of CSM is less than 10% in the vibratory mixing method. As the cement dosage and the vibration acceleration increase, the unconfined compressive strength increases. However, cement dosage has a more significant influence on improving the unconfined compressive strength than the mixing method. With the increase of every 1% in cement dosage, the 7-day strength of conventional mixing and in vibratory mixing average increased by 59% and 38%, respectively. However, the maximum improvement rate of the UCS value is 20–56.7% when vibration acceleration increased from 0 to 1 g. Especially when cement dosage is high, the effect of vibratory mixing on improving strength is limited. Besides, vibratory mixing reduces the original cement dosage by over 1.6% with the qualified unconfined compressive strength at vibration acceleration of 2 g, which is recommended in construction practice.

A non-sampling mixing index for multicomponent mixtures

Cho, Migyung,Dutta, Prashanta,Shim, Jaesool Elsevier Sequoia 2017 Powder technology Vol.319 No.-

<P><B>Abstract</B></P> <P>Uniform mixing is crucial for different types of molecules, powders, and materials in several chemical, mineral, cement, and drug companies. However, there is no effective index to evaluate the uniformity of mixing of multiple components. This study proposes a non-sampling mixing index (SMI) that is applicable to both multiple mixtures with more than two components as well as binary mixtures. The proposed mixing index estimates a mixing state by using all subdomain mixing information for all particles without requiring sampling. In the study, the index was used to predict the mixing of different types of metallic particles in a screw blender. A discrete element based numerical technique was used to determine the transient location of particles in a screw blender at different rotation rates. The effectiveness of the SMI was demonstrated by comparing it with other representative mixing indices. The effectiveness was elucidated using a model of a binary system in which two groups of particles were mixed from 0% (no mixing) to 100% (perfect mixing). The SMI indicated a linear correlation from 0 to near 1 between test mixing conditions and the mixing indices in contrast to other conventional methods that over-predicted the mixing conditions. With respect to the DEM simulation, the SMI displayed values between SMI=0 at the initial stage and SMI=0.9–0.94 at a fully random mixed condition for the rpm ranges corresponding to 15, 30, 45 and 60. The results also indicated that the SMI value of zero occurred at the boundaries with the exception of the bottom and that a considerably lower mixing index was obtained at boundaries as opposed to inner subdomains with respect to the fully random mixed condition (<I>t</I> =20s and rpm=30).</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new method is developed to predict a mixing state in a non-sampling condition. </LI> <LI> The proposed method provides a mixing index for multicomponent mixtures. </LI> <LI> The index provides good linear correlation from unmixed to fully random mixed. </LI> <LI> The proposed method provides spatial distribution of mixing index. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

화력발전소 탈질설비의 암모니아 혼합 관에서 희석 공기와 암모니아의 혼합에 관한 연구

김기호,하지수 한국가스학회 2022 한국가스학회지 Vol.26 No.2

According to reinforce environmental regulations, coal power plants have used selective cata- lytic reduction using ammonia as a reducing agent to reduce the amount of nitrogen oxide generation. The pur- pose of the present study was to derive a mixing device for effectively mixing dilute air and ammonia in the am- monia mixing pipe by performing computational fluid dynamic analysis. The mixing effect was compared by analysing the %RMS of ammonia concentration at the down stream cross section in the mixing pipe and the 16 outlets based on the case 1-1 shape, which is an existing mixing pipe without a mixing device. The mixing de- vice was performed by changing the positions of a square plate on the downstream side of the ammonia supply pipe and an arc-shaped plate on the wall of the mixing pipe. In the case of the existing geometry(Case 1-1), the %RMS of ammonia concentration at the 16 outlets was 29.50%. The shape of the mixing device for Case 3-2 had a square plate on the downstream side of the ammonia supply pipe and an arc plate was installed adjacent to it. The %RMS of ammonia concentration for Case 3-2 was 2.08% at 16 outlets and it could be seen that the shape of Case 3-2 was the most effective mixing shape for ammonia mixing. 강화되는환경규제에따라석탄화력발전소에서는암모니아를환원제로사용하는선택적촉매환원법을이용 하여질소산화물의발생량을감소시키고있다. 본연구에서는전산유동해석을수행하여암모니아혼합관에서희 석공기와암모니아를효과적으로혼합하기위한혼합장치를도출하는것을목적으로수행하였다. 혼합장치가없 는기존혼합관형상인Case 1-1 형상을기준으로혼합관내의후류단면과16개출구에서암모니아농도의%RMS 를비교하여혼합효과를비교하였다. 혼합장치는암모니아공급관후류에사각판과혼합관벽면에원호모양의 판의위치를변경하여수행하였다. 기존형상의경우(Case 1-1)에16개출구에서암모니아농도의%RMS는29.50% 로나타났다. 혼합장치형상이암모니아공급관후류에사각판이있는것과인접한곳에원호판을설치한Case 3-2 형상의16개출구에서암모니아농도의%RMS는2.08%로나타났으며암모니아혼합에가장효과적인혼합형 상임을알수있었다.

Strategies for evaluating distributive mixing of multimodal Lagrangian particles with novel bimodal bin count variance

Park, Chanho,Lee, Jiheon,Cho, Hyungtae,Kim, Youngjin,Cho, Sunghyun,Moon, Il Elsevier 2018 Powder technology Vol.325 No.-

<P><B>Abstract</B></P> <P>The variance among bin counts is one of the most effective and convenient indices to quantify the degree of spatial distributive mixing. Although it is suitable for evaluating the spatial distribution of unimodal particles, many practical particle-mixing processes involve bimodal or multimodal particle systems. Herein, the variance among bimodal bin counts is introduced as a new mixing index to quantify the degree of distributive mixing of bimodal or multimodal particles. Four bimodal particle-mixing systems are assumed and analyzed to evaluate index performance: balanced versus imbalanced and fully versus partially distributed particle systems. As a result, we suggest practical usage and the most effective variation of variances among conventional bin counts and bimodal bin counts to quantify the four bimodal particle-mixing systems. Furthermore, variations of the method for evaluating multimodal mixing are proposed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We proposed a new mixing index for quantifying the degree of mixing. </LI> <LI> The new index is the variance among bimodal bin counts. </LI> <LI> Four bimodal particle-mixing systems are assumed and analyzed. </LI> <LI> Variations of the method for evaluating multimodal mixing are also proposed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

DEM을 이용한 입자 혼합 시뮬레이션과 혼합지수들의 성능 비교

조미경(Migyung Cho) 대한기계학회 2017 大韓機械學會論文集B Vol.41 No.2

식품, 약학 분야 등 많은 산업 분야에서 다른 특징을 가지는 분자 알갱이들을 잘 혼합하는 것은 중요한 작업이다. 컴퓨터 시뮬레이션의 발달로 적정 수준의 혼합 상태를 얻기 위해 먼저 시뮬레이션을 통한 최적의 혼합 조건들을 찾는 작업이 보편화되고 있다. 이에 따라 시뮬레이션 과정에서 혼합 상태를 측정할 수 있는 혼합 지수에 대한 필요성이 증가하고 있다. 현재까지 많이 사용되는 혼합 지수는 두 가지 종류로 분류되는데 첫째는 샘플링을 통한 통계적 기반의 방법이고 두 번째는 전체 입자들을 모두 사용하여 혼합 지수를 계산하는 방법이다. 본 논문에서는 DEM 시뮬레이션으로 입자들을 혼합하는 과정에서 획득한 데이터에 대해 다양한 혼합 지수들을 계산하여 각 혼합 지수들의 성능과 장단점을 비교 분석하였다. 이로써 적절한 혼합지수를 선택하여 사용할 수 있는 실험적 정보를 제시하고자 한다. Mixing of molecular grains having different characteristics is very important in many industries such as the food and pharmaceutical industries. With the development of computer simulations, it is common practice to find the optimal mixing conditions through a simulation before the actual mixing task to estimate the proper level of mixing. Accordingly, there has been an increasing need for a mixing index to measure the mix of particles in the simulation process. Mixing indices, which have been widely used so far, can largely be classified into two types: first is the statistical-based mixing index, which is prepared using the sampling method, and the second is the mixing index that is prepared using all the particles. In this paper, we calculated mixing indices in different ways for the data in the course of mixing the particles using the DEM simulation. Additionally, we compared the performance, advantages, and disadvantages of each mixing index. Therefore, I propose a standard that can be used to select an appropriate mixing index.

병치된 혼색 자극의 시각적 명도 혼합 효과

한은지,박영경 한국색채학회 2024 한국색채학회 논문집 Vol.38 No.3

Seurat's pointillism is a technique that enables the mixing of colors through the audience's perspective by juxtaposing "small and clear" colored points on the canvas without directly mixing the pigment in the palette. This employs the principle of optical mixing in place of physical mixing, with each point exhibiting an independent color. However, when viewed from a distance, the points coalesce to form a new color. This study sought to elucidate the principle of optical color mixing by focusing on the fundamental attributes of colors. To this end, an investigation was conducted to ascertain the correlation between value and optical color mixing. To achieve this, an experiment was designed to evaluate the difference in visual value of a single color that was physically identical to a color in which the two value stages were uniformly mixed in a tiled shape. The experimental stimulation comprised a solid color stimulation serving as a reference and a tiled color stimulation, wherein the two value levels were uniformly mixed in a tiled of the same area ratio for optical mixing. All color stimuli were presented with a neutral saturation value. Furthermore, in accordance with the objective of the study, which was to analyze the pattern of optical mixing due to the density of color(value) mixture and the difference in value between tiled particles, the stimulus with a 10° x 10° field of view was divided into a density range of 10x10 to 70x70, and the value difference (ΔL*) between tiled particles was divided into 20 and 40 stages. It was thus determined that the averaged color value of the solid and tiled colors of all stimulation pairs was identical, but they were perceived as different. Firstly, when the gap was small (ΔL*=20), when the stimulation density was low, the tiled stimulus was evaluated as darker than the solid color, and when the stimulation density was high, the tiled stimulus was evaluated as brighter than the solid color. Conversely, when the value gap between tiled particles was considerable (ΔL*=40), the mean value of the color mixture was assessed to be higher in the majority of mean value stages, with the exception of the mean value stage with a low density of stimulation, where the opposite was observed. The study revealed that the average value of the solid and tiled(mixed) colors of all stimulation pairs was identical, yet they were perceived as distinct colors. Furthermore, there was a tendency for subjects to perceive the colors as either brighter or darker, contingent on the density and value differences.

A numerical study on the flow and mixing in a microchannel using magnetic particles

Le, Thanh Nga,Suh, Yong-Kweon,Kang, Sang-Mo 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.1

We have numerically investigated the characteristics of the flow and mixing in a microchannel using magnetic particles. The main flow is driven by the pressure gradient along the channel, while the secondary flow for the mixing is induced by the drag forces of the particles. Here, the particles can move in the flow due to the strong attraction under the periodically-varying magnetic field generated by electromagnets. For the study, the fractional step method based on the finite volume method is used to obtain the velocity field of the fluid and the trajectories of the particles. This study aims at achieving good mixing by periodically changing the direction of magnetic actuation force in time to activate the interaction between the particles and the flow. The quality of mixing is estimated by considering the mixing index and $Poincar\acute{e}$ section. In this study, parameter studies on the switching frequency, the magnetic actuation force, the number of magnetic particles and so on are performed to understand their effects on the flow and mixing. Results show that the clustering of magnetic particles during the magnetic actuation plays an important part in good mixing. It is also found that the magnetic force magnitude and switching frequency are the two main parameters that make a combined influence on the mixing efficiency. Such a mixing technique using magnetic particles would be an alternative, effective application for the flow and mixing in a microchannel.

Stratification and Salt-wedge in the Seomjin River Estuary under the Idealized Tidal Influence

황진환,장동민,김용훈 한국해양과학기술원 2017 Ocean science journal Vol.52 No.4

Advection, straining, and vertical mixing play primary roles in the process of estuarine stratification. Estuaries can be classified as salt-wedge, partially-mixed or well-mixed depending on the vertical density structure determined by the balancing of advection, mixing and straining. In particular, straining plays a major role in the stratification of the estuarine water body along the estuarine channel. Also, the behavior of a salt wedge with a halocline shape in a stratified channel can be controlled by the competition between straining and mixing induced by buoyancy from the riverine source and tidal forcing. The present study uses Finite Volume Coastal Ocean Model (FVCOM) to show that straining and vertical mixing play major roles in controlling along-channel flow and stratification structures in the Seomjin river estuary (SRE) under idealized conditions. The Potential Energy Anomaly (PEA) dynamic equation quantifies the governing processes thereby enabling the determination of the stratification type. By comparing terms in the equation, we examined how the relative strengths of straining and mixing alter the stratification types in the SRE due to changes in river discharge and the depth resulting from dredging activities. SRE under idealized tidal forcing tends to be partially-mixed based on an analysis of the balance between terms and the vertical structure of salinity, and the morphological and hydrological change in SRE results in the shift of stratification type. While the depth affects the mixing, the freshwater discharge mainly controls the straining, and the balance between mixing and straining determines the final state of the stratification in an estuarine channel. As a result, the development and location of a salt wedge along the channel in a partially mixed and highly stratified condition is also determined by the ratio of straining to mixing. Finally, our findings confirm that the contributions of mixing and straining can be assessed by using the conventional non-dimensional parameters with respect to salt-wedge behavior.