섬유장 분포를 고려한 연신 집속체의 굵기 모사

김종성,허유,Kim, Jong-S.,Huh, You 한국섬유공학회 2008 한국섬유공학회지 Vol.45 No.6

Bundle consists of fibers that have a length distribution, which influences the flow dynamics in a roller drafting process. Since the dynamic behavior of bundle in the flow system can lead to the thickness variation of the output, the fiber length distribution was taken into the dynamic model describing the bundle flow, and the dynamic characteristics and the output bundle thickness were investigated by simulation, while the process factors such as the draft gauge and the draft ratio were considered. Introducing velocity variance models for different fiber length distributions and a simplified sinusoidal velocity variance into the bundle flow dynamics, the output bundle thicknesses were compared each other. The state variables in a steady state showed that the bundle with a uniform fiber length can get a stronger jerk than the bundle with a fiber length distribution, when crossing over the front roller nip line. The bundle flow dynamics could be characterized by oscillatory behavior with a decaying magnitude or an increasing magnitude with an upper limit, which is dependent on the process variables. It was confirmed theoretically that as the draft gauge increases, the output bundle thickness becomes more uniform, while the draft ratio has the opposite effect on the out-put. The critical draft gauge that defines the bordering zone between unstable and stable behavior of the output bundle thickness was about 1. 25 times of the maximum fiber length. The critical draft ratio revealed different results for bundles with a uniform fiber length and a fiber length distribution: for the uniform fiber length the critical draft ratio has a value below than 25, for a fiber length distribution it lies in the zone greater than 25, which demonstrates that the fiber length distributed bundle is roller drafted better that the uniform fiber length bundle. The simplified velocity variance model could be effectively applied to describe the flow dynamics that consists of bundles with a fiber length distribution or even with a uniform fiber length.

개구부 삽입부의 길이가 헬륨 및 공기의 치환류에 미치는 영향

강태일 한국마린엔지니어링학회 1999 한국마린엔지니어링학회지 Vol.23 No.2

This paper describes experimental investigations of helium-air exchange flow through parti-tioned opening. Such exchange flow may occur following rupture accident of stand pipe in high temperature gas cooled reactor. A test vessel with a opening on top of test cylinder is used for experiments. An estimation method of mass increment is developed and applied to measure the exchange flow rate. A technique of flow visualization by Mach-Zehnder interferometer is provided to recognize the exchange flows. Flow measurements are made with partitioned opening for parti-tion rations $H_p/H_1$ in the range 0 to 1 where $H_p$ and $H_1$ are partition length and height of the open-ing respecticely. In the case of $H_p/H_1$ of 0 flow passages of upward flow of the helium and down-ward flow of the air within the opening are unseparated (bidirectional) and the two flows interact exchange flow rate is minimum through range of the partition ratios, Two flow zones i.e. separat-ed(unidirectional)flow zone and unseparated(bidirectional) flow zone exist with increasing the partition. length, The exchange flow rate increases with increasing the separated flow zone. It is found that a maximum exchange flow rate exists at $H_p/H_1$ of 1. As a result fo comparison of the exchange flow rates by changing the partition ration the fluids interaction in the unseparated zone is found to be an important factor on the helium-air exchange flow rate.

천해파와 해류에 의한 해저면 마찰력

유동훈,김지웅 한국해안해양공학회 2000 한국해안해양공학회 논문집 Vol.12 No.3

일방향흐름에 의한 해류의 마찰력 계산을 위하여 Prandtl의 혼합길이 이론을 수심 전구간에 적용하고 난류의 세기와 수리조건에 따라 완난류와 전난류로 분류하여 마찰계수를 산정하는 개수로 마찰계수 산정방법을 제시하였다. 파랑과 해류의 합성류에 의한 해저마찰력을 계산하기 위하여 두 유속의 연직분포를 고려한 BYO 모형을 이러한 흐름특성을 반영하여 개선하였다. BYO 모형은 모든 유속의 연직분포가 해저면으로부터의 직선과 접선으로 만나는 점(Bijker point)을 도출하여 파운동 유속과 해류유속의 합성을 이 점에서 시행하여 일주기의 평균갑을 구하는 모형이다. 일방향흐름의 해류나 천해파에 의한 파운동이나 해저면 가까이 경계층흐름은 완난류, 천이난류, 전난류 등 세가지 종류로 대별된다. 그 중 완난류로 대별하여 두 경우에 대한 합성류 마찰력 산정방법을 제시하였다. The friction factor equation of open channel flow is developed by using Prandtl's mixing length theory and considering the flow characteristics of smooth or rough turbulent flow. BYO model considers vertical velocity profile for the (:omputation of bottom friction of surface waves and current flow. The model computes the mean bottom friction of combined wave-current flow by the vectorial summation of wave velocity and current velocity at Bijker point. The near bottom flow is discriminated by three flow regimes; smooth, transitional and rough turbulent flow. The model, BYO, has been further refined considering the combination of smooth turbulent flow and rough turbulent flow.

재순환유동 예측을 위한 난류모델 개선에 대한 연구

이영모,김철완 한국전산유체공학회 2016 한국전산유체공학회지 Vol.21 No.2

The standard and realizable models are adopted to improve the prediction performance on the recirculating flow. In this paper, the backward facing step flows are used to assess the prediction performance of the recirculation zone. The model constants of turbulence model are obtained by the experimental results and they have a different value according to the flow. In the case of an isotropic flow situation, decaying of turbulent kinetic energy should follow a power law behavior. In accordance with the power law, the coefficients for the dissipation rate of turbulent kinetic energy are not universal. Also, the other coefficients as well as the dissipation coefficient are not constant. As a result, a suitable coefficients can be varied according to each of the flow. The changes of flow over the backward facing step in accordance with model constants of the models show that the reattachment length is dependent on the growth rate() and the models can be improved the prediction performance by changing the model constants about the recirculating flow. In addition, it was investigated for the curvature correction effect of the models in the recirculating flow. Overall, the curvature corrected models showed an excellent prediction performance.

Performance of hollow-fiber flow field-flow fractionation in protein separation

Park, Ilyong,Paeng, Ki-Jung,Kang, Dukjin,Moon, Myeong Hee WILEY-VCH Verlag 2005 Journal of separation science Vol.28 No.16

<P>Since hollow-fiber flow field-flow fractionation (HF FlFFF) utilizes a cylindrical channel made of a hollow-fiber membrane, which is inexpensive and simple in channel assembly and thus disposable, interests are increasing as a potential separation device in cells, proteins, and macromolecules. In this study, performance of HF FlFFF of proteins is described by examining the influence of flow rate conditions and length of fiber (polyacrylonitrile or PAN in this work) on sample recovery as well as experimental plate heights. The interfiber reproducibility in terms of separation time and recovery was also studied. Experiments showed that sample recovery was consistent regardless of the length of fiber when the effective field strength (equivalent to the mean flow velocity at the fiber wall) and the channel void time were adjusted to be equivalent for channels of various fiber lengths. This supported that the majority of sample loss in HF FlFFF separation of apoferritin and their aggregates may occur before the migration process. It is finally demonstrated that HF FlFFF can be applied for characterizing the reduction in Stokes' size of low density lipoproteins from blood plasma samples obtained from patients having coronary artery disease and from healthy donors.</P>

Effects of noncircular air holes on reacting flow characteristics in a micro can combustor with a seven-hole baffle

Kim, W.H.,Park, T.S. Pergamon ; Elsevier Science Ltd 2016 Applied thermal engineering Vol.100 No.-

Turbulent reacting flows in a CH<SUB>4</SUB>-air micro can combustor with a baffle plate of seven holes are numerically investigated by the Reynolds Stress Model. In order to examine the effects of baffle configurations on the flow structure, the type of air hole is adopted as circle, square, and triangle. The flame zone strongly depends on the relative positions of air and fuel holes, and the flames are developed to a lobed form depending on the number of air holes. Also, when the circular air hole is changed to square or triangular hole, the development of the central recirculation is more obvious for the reacting flows. Such flow structures promote the decay of the streamwise velocity and increase the turbulent mixing. As a result, the triangular hole baffle gives the shortest flame length. It is recognized that the axis-switching phenomenon is included in the three-dimensional flow development. So to investigate the axis-switching effect on the flow and thermal field, two inlet boundary conditions are tested for the triangular hole baffle. The result shows that the axis-switching flow contributes to the shorter flame length. For the modified inlet without the axis-switching, the flame length becomes twice the original size of the axis-switching condition. Additionally, the combustion efficiency is discussed by the conversion rate and heat loss.

수평관 내 물-공기 이상류 거동에 관한 실험적 연구

조한일 ( Hanil Cho ),이경수 ( Kyungsu Lee ),류시완 ( Siwan Lyu ) 한국안전학회(구 한국산업안전학회) 2017 한국안전학회지 Vol.32 No.1

A series of laboratory experiments has been performed in order to investigate the behavior of water-air two-phase flow in a horizontal pipe. A conductivity meter has been applied to detect the irregular alternation of air at the specific points in flows. The experimental condition has been established according to the water and air flowrates. Passing time, which is the time length for a measuring probe to pass through the entire length of a specific bubble, has been defined to evaluate the size of bubbles in the flow. Passing length, which can be considered as the equivalent value to bubble size and determined from the product of passing time and cross-sectional averaged velocity, and its corresponding occurrence frequency have been analyzed to classify the air flow patterns according to the condition of air and water fluxes. From the result, the dependancy of flow patterns on the variation of air-water flux ratio has been investigated and the existence of thresholds also checked for classifying the behavior of air in the flow.

Molecular simulation study of water transport through aquaporin-inspired pore geometry

마지드,김대중 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.8

Water permeation dynamics through hourglass-shaped nanopore is addressed by using Molecular dynamics (MD) simulations. The objective of this research is to understand the variation of the length on water transport in hourglass-shaped pore. We found that the water flow decreases with length due to the hydrodynamic resistance at the entrances, that has large contribution on water flow. Moreover, it was shown that water flux decreases as the length increases, which is consistent with the experimental study. The fluctuations of the density profiles at the center of the pore reduce as the length increases, which is an indication of fast local permeability through highly continuous motion. The pore surface becomes highly frictionless with increasing the length due to the low water-wall interaction. On the other hand, the hydrodynamic resistance (viscos dissipation) at the center of the pore decreases as the length increases, whereas the entrance effect can be highlighted. The MSD curve indicates a Fickian diffusion with increasing the length, even though a Single-file diffusion is expected. It can be found that the changing the cone angle affects on flow rate enhancement through hourglass-shaped nanochannels.

재순환유동 예측을 위한 k-ɛ 난류모델 개선에 대한 연구

이영모(Y.M. Lee),김철완(C.W. Kim) 한국전산유체공학회 2016 한국전산유체공학회지 Vol.21 No.2

The standard k-ɛ and realizable k-ɛ models are adopted to improve the prediction performance on the recirculating flow. In this paper, the backward facing step flows are used to assess the prediction performance of the recirculation zone. The model constants of turbulence model are obtained by the experimental results and they have a different value according to the flow. In the case of an isotropic flow situation, decaying of turbulent kinetic energy should follow a power law behavior. In accordance with the power law, the coefficients for the dissipation rate of turbulent kinetic energy are not universal. Also, the other coefficients as well as the dissipation coefficient are not constant. As a result, a suitable coefficients can be varied according to each of the flow. The changes of flow over the backward facing step in accordance with model constants of the k-ɛ models show that the reattachment length is dependent on the growth rate(λ) and the k-ɛ models can be improved the prediction performance by changing the model constants about the recirculating flow. In addition, it was investigated for the curvature correction effect of the k-ɛ models in the recirculating flow. Overall, the curvature corrected k-ɛ models showed an excellent prediction performance.

기체주입 충돌제트의 분무특성에 관한 실험적 연구

이근석,윤영빈,안규복 한국분무공학회 2019 한국액체미립화학회지 Vol.24 No.4

The effervescent atomizer is one of twin-fluid atomizers that aeration gas enters into bulk liquid and two-phase flow is formed in the mixing section. The effervescent atomizer requires low injection pressure and small amount of aeration gas, as compared to other twin-fluid atomizers. In this study, cold flow test was conducted to investigate the spray characteristics of aerated impinging jets. The present effervescent impinging atomizers were composed of the aerator device and like-on-like doublet impinging atomizer which had different impinging angles. To analyze the spray characteristics such as breakup length and droplet size distribution, the image processing technique was adopted by using instantaneous images at each flow condition. Non-dimensional parameters, induced by the homogeneous flow model, were used to predict the breakup length. The breakup length was decreased with the mixture Reynolds number and impinging angle increasing. The result of droplets showed that the size distribution was axisymmetric about the center of the injector and their diameter tended to decrease with increasing GLR.