유량변화에 따른 판형열교환기의 압력강하와 내부유동 가시화에 관한 실험적 연구

황주원(Ju Won Hwang),김덕규(Deok Gyu Kim),박창용(Chang Yong Park) 대한설비공학회 2019 대한설비공학회 학술발표대회논문집 Vol.2019 No.-

This study was carried out to measure the pressure drop and visualize the flow in the flow path between the chevron corrugated two plates in a heat exchanger. A test section was made to visualize the flow characteristics in the flow channels formed by a metal real heat exchanger plate and transparent replica of the counterpart plate. A simple closed loop test facility was made to do the experiment with the change of volume flow rate. The visualization was performed by a high speed camera with 800 fps and air bubbles were injected in the flow to visualize the flow distribution in the channels on the two plates. The measured pressure drop agreed well with the general trend of the pressure drop change with the increase of flow rate. The visualized flow patterns showed that the flow was not evenly distributed in the channels between the two plates, due to the left-sided inlet and outlet location od the flow. The flow visualization with air bubbles showed the limitation to visualize the actual flow velocity distribution on the two plates because Buoyant effect was dominant under upward flow conditions.

Efficient blood flow visualization using flowline extraction and opacity modulation based on vascular structure analysis

Kwon, Ohjae,Lee, Jeongjin,Kim, Bohyoung,Shin, Juneseuk,Shin, Yeong-Gil Elsevier 2017 Computers in biology and medicine Vol.82 No.-

<P><B>Abstract</B></P> <P>With the recent advances regarding the acquisition and simulation of blood flow data, blood flow visualization has been widely used in medical imaging for the diagnosis and treatment of pathological vessels. In this paper, we present a novel method for the visualization of the blood flow in vascular structures. The vessel inlet or outlet is first identified using the orthogonality metric between the normal vectors of the flow velocity and vessel surface. Then, seed points are generated on the identified inlet or outlet by Poisson disk sampling. Therefore, it is possible to achieve the automatic seeding that leads to a consistent and faster flow depiction by skipping the manual location of a seeding plane for the initiation of the line integration. In addition, the early terminated line integration in the thin curved vessels is resolved through the adaptive application of the tracing direction that is based on the flow direction at each seed point. Based on the observation that blood flow usually follows the vessel track, the representative flowline for each branch is defined by the vessel centerline. Then, the flowlines are rendered through an opacity assignment according to the similarity between their shape and the vessel centerline. Therefore, the flowlines that are similar to the vessel centerline are shown transparently, while the different ones are shown opaquely. Accordingly, the opacity modulation method enables the flowlines with an unusual flow pattern to appear more noticeable, while the visual clutter and line occlusion are minimized. Finally, Hue-Saturation-Value color coding is employed for the simultaneous exhibition of flow attributes such as local speed and residence time. The experiment results show that the proposed technique is suitable for the depiction of the blood flow in vascular structures. The proposed approach is applicable to many kinds of tubular structures with embedded flow information.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An improved method for visualizing blood flow in vascular structures is proposed. </LI> <LI> The proposed method automates the seeding process. </LI> <LI> Our method resolves the early termination of flowline integration in curved vessels. </LI> <LI> Our method adjusts the visibility of flowlines by attenuating the opacity. </LI> <LI> Our method enables a faster diagnosis through the depiction of abnormal flow. </LI> </UL> </P>

유동 가시화를 이용한 PCHE의 유동분배에 관한 실험적 연구

설한이,손상호,이공훈,김정철 대한설비공학회 2023 설비공학 논문집 Vol.35 No.1

PCHE, Printed Circuit Heat Exchanger, is widely used for industrial applications with increasing demand in extreme environments. As interest in hydrogen for future fuel is increased, the interest in PCHE is also increased. In this study, we focused on the flow distribution in channels of PCHE. Although flow distribution has been employed a lot of times for decades, there are few reliable studies based on experimental results that can be directly applied in actual industrial fields. Here, we introduce experimental results about flow distribution by flow visualization. Effects of flow rates and the verticality are addressed to clarify the difference in distribution. When the flow rate is low, the flow speed difference between channels is not significantly large. If it becomes larger, the difference becomes large. Moreover, when inlet and outlet pipes are installed at a slight angle, back flow is observed. The speed profile of the tilted case in high flow rate is not easily predicted. Although the tilting angle looks very small, the measured speed profile can be completely different. 본 연구에서는 PCHE에 유입되는 유동의 방향 및 유량에 따른 불균등도에의 영향을 알아보기 위해 유동가시화 실험을 진행하였다. 일반적으로 고유량에서는 불균등도가 더욱 증가하였고, 저유량에서는 감소하였다. 또한, 액체가 중앙에서 수직방향으로 유입될 때, 저유량에서 더욱 대칭적인 속도장이 관찰되었다. 유입 방향의 경우, 작은 정도로만 기울어져도, 유동 불균등도가 증가할 뿐만 아니라, 역방향 유동이 발생할 정도로 수직인 경우와 큰 차이를 보였다. 본 연구의 실험 결과는 실제 산업의 PCHE와 비교해 볼 때, 비교적 큰 헤더를 사용한 경우에 해당된다. 따라서 헤더 내부의 chaotic 유동이 더욱더 극대화된 것으로 생각된다. 다만, 실제는 헤더의 종횡비가 더욱 큰 경우가 많고, 채널 내 평균 유속도 본 실험의 약 50 cm/s보다 더 큰 경우도 있기 때문에, 실제 산업에서의 불균등도는 더욱 안 좋을 수도 있다. 따라서 여러 가지 다양한 경우에 대해, 실질적인 유동 분배 문제가 실험적으로 밝혀져야 한다. 또한, 향후에는 최외곽 채널에 대한 분석 이외에도 내부 유동에 대한 분석도 이루어져야 하고, 기체를 포함한 다른 유체에 대해서도 분석이 이루어져야 한다. 그리고, 채널 방향과 수직인 경우 및 입출구 배관 크기의 영향 등에 대해서도 심도있는 연구가 이루어져야 할 것이다.

터빈 캐스케이드 유동의 가시화기법에 대한 연구

신홍숭,김창훈,전창수 한국 항공대학교 항공산업기술연구소 2001 航空宇宙産業技術硏究所 硏究誌 Vol.11 No.-

벽면에서의 전단응력 분포와 유동장 내에서의 유동 요소를 추적하는 유동가시화 기법 중에서 몇 가지를 그 응용 예와 함께 살펴보았다. 유동의 주요 특징들과 한계유선(limiting streamlines)을 관찰하기 위해서는 유막법이 충분하나 유속이 작거나 유동의 방향이 분명하지 않은 곳에서는 ink dot 기법을 적용하는 것이 좋다. 유막법은 실험하고자 하는 유동의 조건에 따라 기름과 분말의 혼합비, 기름의 점도등을 잘 선택하여야 한다. 유막법으로 확인 할 수 있었던 터빈 블레이드의 유동의 기본 메카니즘을 구성하는 특성있는 유동은 말발굽와류, 끝벽 재부착선chment line), 안장점 (saddle point), 흡입면 와류 (leading edge suction side vortex), 압력면 와류 (leading edge pressre side vortex), 흡입면 모서리 와류 (suction side corner vortek), 뒷전와류를 확인 할 수 있었다. Flow visualization techniques are applied in turbine cascade flow to show shear stress distributions at the wall and find fundamental flow mechanism. For flow mechanism and limiting streamlines, oil film method was feasible, but for flow regimes of low velocity and uncertain flow direction, ink dot method was more superior than others. Best conditions on mixing ratios of oil and powder and oil viscosity, which were strongly dependent on flow conditions, was very important in showing better visualizations. These must be selected by triad and error and experiences. Using oil film method, horseshoe vortex, endwall reattachment line, saddle points leading edge suction side vortex, leading edge pressure side vortex, suction side comer vortex, and trailing edge vortex, which are fundamental flow characteristics of so-called secondary flow in turbine cascades, were observed.

Fluid Dynamic Efficiency of an Anatomically Correct Total Cavopulmonary Connection: Flow Visualizations and Computational Fluid Dynamic Studies

Yun, S.H.,Kim, S.Y.,Kim, Y.H. Biomedical Engineering Society for Circulation 2003 International Journal of Vascular Biomedical Engin Vol.1 No.2

Both flow visualizations and computational fluid dynamics were performed to determine hemodynamics in a total cavopulmonary connection (TCPC) model for surgically correcting congenital heart defects. From magnetic resonance images, an anatomically correct glass model was fabricated to visualize steady flow. The total flow rates were 4, 6 and 8L/min and flow rates from SVC and IVC were 40:60. The flow split ratio between LPA and RPA was varied by 70:30, 60:40 and 50:50. A pressure-based finite-volume software was used to solve steady flow dynamics in TCPC models. Results showed that superior vena cava(SVC) and inferior vena cava(IVC) flow merged directly to the intra-atrial conduit, creating two large vortices. Significant swirl motions were observed in the intra-atrial conduit and pulmonary arteries. Flow collision or swirling flow resulted in energy loss in TCPC models. In addition, a large intra-atrial channel or a sharp bend in TCPC geometries could influence on energy losses. Energy conservation was efficient when flow rates in pulmonary branches were balanced. In order to increase energy efficiency in Fontan operations, it is necessary to remove a flow collision in the intra-atrial channel and a sharp bend in the pulmonary bifurcation.

Fluid Dynamic Efficiency of an Anatomically Correct Total Cavopulmonary Connection: Flow Visualizations and Computational Fluid Dynamic Studies

Yun, S.H.,Kim, S.Y.,Kim, Y.H. Biomedical Engineering Society for Circulation 2004 International Journal of Vascular Biomedical Engin Vol.2 No.1

Both flow visualizations and computational fluid dynamics were performed to determine hemodynamics in a total cavopulmonary connection (TCPC) model for surgically correcting congenital heart defects. From magnetic resonance images, an anatomically correct glass model was fabricated to visualize steady flow. The total flow rates were 4, 6 and 8L/min and flow rates from SVC and IVC were 40:60. The flow split ratio between LPA and RPA was varied by 70:30, 60:40 and 50:50. A pressure-based finite-volume software was used to solve steady flow dynamics in TCPC models. Results showed that superior vena cava(SVC) and inferior vena cava(IVC) flow merged directly to the intra-atrial conduit, creating two large vortices. Significant swirl motions were observed in the intra-atrial conduit and pulmonary arteries. Flow collision or swirling flow resulted in energy loss in TCPC models. In addition, a large intra-atrial channel or a sharp bend in TCPC geometries could influence on energy losses. Energy conservation was efficient when flow rates in pulmonary branches were balanced. In order to increase energy efficiency in Fontan operations, it is necessary to remove a flow collision in the intra-atrial channel and a sharp bend in the pulmonary bifurcation.

Three-Dimensional Flow Visualization for the Steady and Pulsatile Flows in a Branching Model using the High-Resolution PIV System

Suh, Sang-Ho,Roh, Hyung-Woon Biomedical Engineering Society for Circulation 2004 International Journal of Vascular Biomedical Engin Vol.2 No.2

The objective of the present study is to visualize the steady and pulsatile flow fields in a branching model by using a high-resolution PIV system. A bifurcated flow system was built for the experiments in the steady and pulsatile flows. Harvard pulsatile pump was used to generate the pulsatile velocity waveforms. Conifer powder as the tracing particles was added to water to visualize the flow fields. CCD cameras($1K{\times}1K$(high resolution camera) and $640{\times}480$(low resolution camera)) captured two consecutive particle images at once for the image processing of several cross sections on the flow system. The range validation method and the area interpolation method were used to obtain the final velocity vectors with high accuracy. The results of the image processing clearly showed the recirculation zones and the formation of the paired secondary flows from the distal to the apex of the branch flow in the bifurcated model. The results also indicated that the particle velocities at the inner wall moved faster than the velocities at the outer wall due to the inertial force effects and the helical motions generated in the branch flows as the flow proceeded toward the outer wall. Even though the PIV images from the high resolution camera were closer to the simulation results than the images from the low resolution camera at some locations, both results of the PIV experiments from the two cameras generally agreed quite well with the results from the computer simulations. Therefore, instead of using the expensive stereoscopic PIV or 3D PIV system, the three-dimensional flow fields in a bifurcated model could be easily and exactly investigated by this study.

LDV Measurement, Flow Visualization and Numerical Analysis of Flow Distribution in a Close-Coupled Catalytic Converter

Kim, Duk-Sang,Cho, Yong-Seok The Korean Society of Mechanical Engineers 2004 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.18 No.11

Results from an experimental study of flow distribution in a close-coupled catalytic converter(CCC) are presented. The experiments were carried out with a flow measurement system specially designed for this study under steady and transient flow conditions. A pitot tube was a tool for measuring flow distribution at the exit of the first monolith. The flow distribution of the CCC was also measured by LDV system and flow visualization. Results from numerical analysis are also presented. Experimental results showed that the flow uniformity index decreases as flow Reynolds number increases. In steady flow conditions, the flow through each exhaust pipe made some flow concentrations on a specific region of the CCC inlet. The transient test results showed that the flow through each exhaust pipe in the engine firing order, interacted with each other to ensure that the flow distribution was uniform. The results of numerical analysis were qualitatively accepted with experimental results. They supported and helped explain the flow in the entry region of CCC.

웹기반 데이터 시각화 도구를 활용한 플로우 데이터의 지리적 시각화 기법 탐색

김지우,이건학 한국지도학회 2017 한국지도학회지 Vol.17 No.1

플로우 데이터는 지역간 공간적 상호작용이나 상호작용에 따른 공간 조직의 형성과 변화 등을 분석하고 이해하는데 중요한 자료로 활용되고 있다. 플로우 데이터에 대한 전통적인 지도학적 시각화 방법으로 널리 사용되고 있는 유선도는 복잡하고 많은 유선의 표현에 따른 낮은 가독성이나 중첩성 등이 한계로 지적되고 있다. 이에 본 연구는 최근 비공간적 데이터 뿐 아니라 공간 데이터의 새로운 재현 방법으로 각광받고 있는 정보 시각화 도구에 주목하여, 플로우 데이터의 지리적 시각화 기법으로서 정보 시각화 도구의 적용가능성을 탐색하고 각 기법에 대한 유용성을 체계적으로 평가하고자 한다. 이를 위해 자바스크립트 기반의 데이터 시각화 라이브러리인 D3.js의 강제 유향 그래프, 코드 다이어그램, 위계적 엣지 번들링, 생키 다이어그램, 시간 거리 그래프를 활용하였으며, 실제 고속 철도 운행 플로우에 대한 다양한 시각화 사례를 실제로 개발하여 보여주고 있다. 사례 분석 결과, 각 정보 시각화 기법은 전통적인 유선도가 갖는 한계들을 효과적으로 극복할 수 있으며, 플로우 데이터에 대한 대안적인 시각화 기법으로 유용하다는 것을 확인할 수 있었다. 또한 이를 통해 본 연구는 플로우 데이터의 지리적 시각화 분야에 유용한 가이드라인을 제공할 수 있고, 지리학, 지도학 및 공간 정보 분야에서 공간 정보의 매핑과 시각화 방법에 대한 인식적 변화를 가져올 것으로 기대한다. Flow data have been utilized for analyzing and understating a regional spatial interaction and the dynamics of spatial organization by spatial interaction. As a classical cartographic visualization method, flow map has been broadly used for representing flow data. A flow map, however, has technical limitations such as lower readability and occlusion by representing complicated many flows. In this regard, this research focuses on an information visualization tool which has been paid attention as a new approach for representing not only non spatial data but also spatial data. We attempt to explore the applicability of a information visualization tool for geovisualization of flow data and evaluates the usability of various information visualization graphs. To do this, we utilize several graphs of Java script library of D3.js, including forced-directed graph, chord diagram, hierarchical edge bundling, Sankey diagram, and time-distance graph and present various geovisualization ways of rapid-trasit railway flows. From a result of case study, it turns out that each of information visualization techniques is able to overcome limitations of a traditional flow mapping technique in an effective way, and is quite useful as an alternative way of visualizing flow data. Also, it is expected that this paper provides a useful guideline for geovisualization of flow data, and leads a cognitive change of spatial information mapping and visualization in geography, cartography, and other areas dealing with spatial information.

Flow Characteristics of Pulp Suspension in a 90° Bend

Masaru Sumida,Kentaro Imamura 한국유체기계학회 2020 International journal of fluid machinery and syste Vol.13 No.2

This study investigates the flow characteristics of pulp suspensions flowing through a 90° bend, which is used in the production system of an actual papermaking machine, e.g., for transporting the pulp suspensions from its stock reservoir to the header. Experiments were conducted on pulp suspensions with a fiber concentration Cs of 0.3 and 0.6 wt% and a bend with a diameter of 22 mm and a curvature radius ratio of 4.0. Flow visualization and measurements of the distributions of time-averaged fiber concentration Ca and axial velocity U were performed with a light section method and the particle image velocimetry (PIV) method, respectively, at representative bulk velocities and at various longitudinal stations. The influence of the flow rate on the changes of their distributions in the streamwise direction was examined. The flow characteristics of the pulp suspension depend on the flow pattern in the upstream straight tube and are greatly different from those of the single-phase water flow. For a low flow rate, the flocculated pulp fibers move without getting disentangled in the bend and the distribution of Ca shows a shape bias towards the inner wall side. As the flow rate is increased, Ca becomes larger in the outer part of the bend, and it changes into a rather flat distribution in the downstream tangent.