Heat transfer characteristics in a channel fitted with zigzag-cut baffles

Chayut Nuntadusit,Ibroheng Piya,Makatar Wae-hayee,Smith Eiamsa-ard 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.6

The heat transfer characteristics were experimentally investigated in a wind channel with different types of cut baffles for heat transferaugmentation. The aim of using zigzag-cut baffles is to create 3D flow structure behind the baffles instead of transverse vortex flow leadingto enhance heat transfer. In this study, 4 types of baffles were examined; conventional baffle (Rectangular cross section with no cut),baffle with rectangular zigzag-cut, baffle with triangle zigzag-cut at 45 degree and at 90 degree. All of the baffles have the same height atH = 15 mm and flow blocking area. In the experiment, the row of seven baffles was attached on the inner surface of wind channel. Theeffects of pitch spacing length were also investigated at baffle pitch distance P/H = 4, 6 and 8 (H: Height of baffle). The experimentswere performed at constant Reynolds number (Re) of 20000. The heat transfer patterns via Thermochromic liquid crystal sheet werevisualized and recorded with a digital camera. The recorded images were then analyzed with image processing technique to obtain thedistribution of Nusselt number. The flow characteristics pass through the baffles were also numerically studied with CFD simulation forunderstanding the heat transfer characteristics. The friction losses were measured to evaluate the thermal performance for each baffle. Itwas found that the baffle with rectangular zigzag-cut gives the best thermal performance due to heat transfer augmentation in upstreamand downstream side of baffle.

PEM 연료전지 평행류 채널에서 Baffle의 영향

오창묵(Chang-Mook Oh),이규정(Kyu-Jung Lee) 대한설비공학회 2008 대한설비공학회 학술발표대회논문집 Vol.2008 No.2

The effects of baffles in PEM fuel cell with parallel flow channel has been simulated by using conmmercial program. The simulation has been conducted through the channel and there are four different heights of baffles, No Baffle(Hb=0), Partially Blocked Baffle(0.25, 0.5, 0.75), Fully Blocked Baffle(1) conditions. The result shows that current density changes while placing a baffle at the various positions along the channel. Current density with a single baffle is higher than that without baffle and current density using Fully Blocked Baffle(FBB) is much higher than current density using Partially Blocked Baffle(PBB). When the baffle is closer to outlet of the channel, current density increases. It is found that pressure is related to current density. If the pressure is higher, the better performance will be expected.

교반속도 및 Baffle 각도 조절에 따른 침전지 효율 최적화 연구

곽성근,김충곤 유기성자원학회 2020 유기물자원화 Vol.28 No.4

This study was conducted to improve the solid-liquid separation efficiency of clarifiers. To do so, the study did a bio-flocculation experiment simply by controlling the stirring speed (rpm) and baffle angle of a clarifier on a lab scale, but without using a coagulant. For the purpose of the experiment, the feed wall of a clarifier was so improved that a baffle could be installed on the clarifier. Then, it was ensured to change its stirring speed (to 0.0rpm, 0.6rpm, and 1.2rpm), with the angle fixed at 10°. As a result, it was found that concentration efficiency increased by 2.0%, and effluent removal efficiency (SS concentration) by 7.8%, at a stirring speed of 0.6ppm. This indicates the bio-coagulation efficiency of sludge increased with changing stirring speeds. Then, the baffle angle of the sedimentation unit was changed to analyze how the changed baffle angle would affect the sedimentation of sludge. As a result, it was found that the compression of sludge interface was very effective at a baffle angle of 20°. It is hoped that these experimental findings will be useful in improving the sedimentation efficiency of circular clarifiers. 본 연구에서는 원형침전지의 고액분리 효율을 향상시키기 위해 응집제 없이 lab scale 침강장치에 교반속도(rpm)와 baffle 각도를 조절하여 생응집(bio-flocculation) 실험을 수행하였다. 피드 웰(feed wall)부분을 개량하여 baffle 를 설치하고 각도(10°)를 고정한 후 각각의 교반속도(0.0rpm, 0.6rpm, 1.2rpm) 변화에 따른 실험 결과 교반속도 0.6ppm 에서, 농축효율이 2.0%, 유출수(SS 농도) 제거효율은 7.8% 상승되는 것으로 분석되어 교반속도에 따른 슬러지의생응집 효율 향상을 확인할 수 있었다. 또한, 침강장치 baffle의 각도를 변화시켜 슬러지 침강특성 영향을 분석한결과 baffle 각도 20°에서 슬러지 계면층의 압축이 매우 높게 나타났다. 본 연구결과는 원형침전지의 침전 효율향상을 위한 기초 인자로 활용이 기대된다.

소형 SCR 시스템 내 유동 제어를 위한 Baffle의 구조 결정에 관한 수치해석적 연구

박미정(Mi Jung Park),장혁상(Hyuk Sang Chang),하지수(Ji Soo Ha) 大韓環境工學會 2010 대한환경공학회지 Vol.32 No.9

소형 SCR 시스템(처리용량 25,300 Sm3/hr, 내부용적 2.4×2.4×3.1 m3)의 촉매성능개선을 목적으로 배기가스 유동제어에 관한 수치 해석적 연구가 수행되었다. 유동제어를 위해 여러 형태의 배플이 제안되었으며 CFD 해석을 통해 최적의 배플형상을 결정하였다. 유동 균일화를 위해서 설치된 배플의 유무에 따라 본 연구의 SCR 시스템에서의 촉매층 전단 5 mm에서 유속에 대한 RMS(%) 값은 약 6.2%의 차이를 보였다. 수치해석에 의해 결정된 격자 형상의 배플에서 사용된 배플판의 두께범위가 0~8 mm에서는 RMS(%) 값의 변화가 없었으나 두께 10 mm가 되면 2.5% 가량 수치가 증가하여 유동에 영향을 주었다. 격자 형상의 배플은 원뿔대 형상, 믹서 형상 배플에 비해 상대적으로 높은 유동안정도를 나타내며 형상에 따라 RMS(%) 값은 10% 이상의 차이를 나타내었다. Numerical analysis was done to evaluate the gas flow distribution in small scale SCR system which has 2.4×2.4×3.1 m3 in volume and 25,300 Sm3/hr in flue gas flow capacity. Various types of baffles proposed for controlling the flow uniformity were evaluated by the CFD analysis to find the optimal geometry of the baffle in the SCR system. By installing baffles in the SCR system, the RMS (%) value was raised up to 6.2% compared with the baffle-uninstalled state. The effect of baffle thicknesses on the RMS (%) value was not shown within 0 and 8 mm in thickness, but the RMS (%) value was raised by 2.5% in 10 mm of baffles thickness, which causes the unstability in flow. By comparison between the shape of baffles, it is known that the lattice type baffle has better performance in controlling the flow uniformity than the circular truncated cone type baffle or mixer type baffle. RMS (%) values have more that 10% difference according to the shape of baffle type.

Baffle이 있는 핀틀-노즐 추력기의 압력 거동

진정근(Jungkun Jin),오석진(Seokjin Oh),이지형(Ji Hyung Lee),하동성(Dong Sung Ha),박성한(Sunghan Park),양준서(Juneseo Yang) 한국추진공학회 2013 한국추진공학회 학술대회논문집 Vol.2013 No.12

핀틀 노즐 기술을 적용한 고체 추진기관의 지상 연소시험을 수행하여 내탄도 성능 해석과 비교하였다. Baffle이 없는 핀틀-노즐 추진기관 시험 결과 초기 압력은 내탄도 성능 해석 결과와 유사하였으나 점진적으로 압력이 증가하는 현상이 나타났다. 또한, 핀틀로 공급되는 유동을 균일하기 위하여 baffle을 추가하여 시험을 수행하였다. 시험 결과 예측되는 압력보다 40% 높은 압력이 측정되었으며 CFD 유동 해석을 통하여 baffle에 의한 전압력 손실이 발생하며 전압력 손실을 고려하여 예측된 연소실 압력이 측정 압력과 유사함을 확인하였다. Firing test of solid rocket motor with pintle-technology was carried out to compare the pressure-time curve obtained by internal ballistic and performance analysis. Without baffle, the measured combustion chamber pressure was similar with the predicted pressure and progressive burning was observed with end-burning grain. A baffle was inserted to make uniform flow over the pintle and tested. Unlike the thruster without baffle, the measured combustion chamber pressure was 1.4 times higher than the predicted value. In CFD simulation, 10% of total pressure loss was observed from combustion chamber to nozzle throat with the baffle. The measured pressure with baffle was predicted well by considering the total pressure loss in the internal ballistic modelling and performance analysis.

Simulation of Various Baffle Types in a Constructed Wetland Sedimentation Tank using CFD

Taegyun Noh,Jechan Jeon,Lee-Hyung Kim 한국습지학회 2016 한국습지학회지 Vol.18 No.3

인공습지는 오염물질 저감기능을 포함하는 여러 가지 생태서비스 기능 때문에 다양하게 적용되고 있다. 그러나 인공습 지에 많은 입자상 물질이 유입하게 되면 유지관리의 어려움과 기능의 저하를 초래한다. 따라서 본 연구는 인공습지 내 입자상 물질의 제거효율 향상을 위한 침강지내 최적 baffle 설치방안을 도출하고자 수행되었다. 최적 저류판 설치방안 은 침강지내 유체와 입자의 흐름을 해석함으로써 도출가능하며, 이를 위해 전산유체역학(Computational Fluid Dynamics, CFD) 이론을 활용하였다. 연구결과는 baffle이 유속을 저하시키고 입자상 물질의 침강효율을 증가시키는 것으로 나타났으며, 경사각을 가진 저류판보다는 수직 저류판이 효과적인 것으로 나타났다. 이러한 연구결과를 활용하 여 공공지역 비점오염저감시설로 설치된 소규모 하이브리드 인공습지의 침강지 효율개선 방안을 도출하였다. 수직각을 이용한 저류판을 설치할 경우 침강효율이 1.2~1.3배 정도 증가하는 것으로 나타났다. 이러한 침강지 내 저류판의 설치 에 따른 결과는 인공습지의 전반적인 저감 효율을 증가시킬 뿐만 아니라 유지관리 빈도를 줄임으로써 비용효율적 인공 습지 설계에 기여할 것으로 평가된다. Constructed wetlands are widely applied in urban and rural areas for various purposes such as pollutants reduction, acquisition of eco-spaces and habitats, flooding reduction, acquisition of water resources and environmental education. Since the design of constructed wetlands utilizes ecosystems, special consideration must be given to ecological mechanisms, environmental mechanisms and hydrological mechanisms. To ensure the sustainable functionality of constructed wetlands, it is necessary to achieve stable flow rate and velocity, and remove sediments to ensure sufficient space for detention. To enhance the efficiency of constructed wetland sedimentation basins, this study determined the optimal position for baffle installation, and applied Computational Fluid Dynamics (CFD) to the cross-sectional design of wetlands. CFD analysis revealed that the decrease in flow velocity with baffle installation enhanced the efficiency of sedimentation of particulate matters. Vertical baffles had higher sedimentation efficiency than those with an inclined angle. When vertical baffles were installed in the sedimentation basin of a hybrid constructed wetland to reduce non-point source pollutants in urban areas, the average flow velocity within the basin decreased by 10~30%, while the sedimentation efficiency improved by 1.3~1.5 times. The application of CFD to constructed wetlands is expected to improve the cost efficiency of designing hybrid constructed wetlands with high removal efficiency.

정류공의 형태 및 유공율 변화에 따른 정류효과

최계운 ( Choi Gye-woon ),김현수 ( Kim Hyun-soo ),김사동 ( Kim Sa-dong ) 한국환경기술학회 2001 한국환경기술학회지 Vol.2 No.3

본 논문에서는 정류공의 형태 및 유공율 변화에 따른 정류효과를 얻기 위한 실험이 실시되었다. 실험은 파일롯트 플랜트를 이용하여 실시되었으며, 12㎥/일 규모의 파일롯트 플랜트가 설치되었고, 원형 정류공, 양단 축소형, 하단 축소형 등 3개의 정류공이 정류효과를 검토하기 위하여 설치되었다. 정류효과는 침전된 슬러지의 양, 탁도 제거 효율, 형광액을 이용한 흐름특성에 따라 평가되었다. 실험결과 하단 축소형 정류공을 가진 정류벽의 효과가 원형 정류공이나 양단 축소형 정류공을 가진 정류벽에 비하여 더 나았다. 유공를 변화에 따른 실험에서 유공율이 6.3%와 8.0%인 정류벽의 정류효과는 유공율이 4.5%인 정류벽에 비하여 정류효과가 크게 개선되는 것으로 나타났다. 만약 침전지 입구에 하단 축소형 정류공을 가진 정류벽이 설치된다면 원형이나 양단축소형 정류공을 가진 정류벽에 비하여 정류효과를 크게 개선시킬 것이다. In this paper, the experiments to obtain the effects of baffles by the variations of baffle type and opening rate were conducted. The experiments are conducted using the pilot plant. The pilot plant having the capacity of 12㎥/day was installed and the baffles having three different opening holes, which are the circular, upward and downward contracted, and downward contracted holes, are utilized to investigate the effects of baffles. The effects were evaluated depending upon the settled sludge volume, turbidity removal efficiency and flow characteristics examined using the fluorescent material. The results show that the effect of the baffle having the downward contracted holes is better compared to the baffles having two different types of opening holes. In the experiments by the variation of the opening rates, the baffle effects are greatly improved when the opening rate of 4.5% is increased until 6.3% to 8.0%. If the baffles having downward contracted holes are used in the sedimentation basin, the baffle effects are greatly increased compared to the baffles having the circular holes or upward and downward contracted holes.

배플이 설치된 잠수함 압축기용 오일 냉각기의 전열 성능에 관한 수치연구

이관근(Kwan Geun Lee),이준경(Jun Kyoung Lee),방영준(Young Jun Bang),신환준(Hwan Jun Shin),장덕호(Deok ho Jang),정금수(Keum Soo Jeong) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12

Ultra high pressure air compressor for special ships, including submarines needs to be developed to reduce the weight and volume. Related with the components of new type compressor, it is necessary to develop the shell and tube type heat exchanger(HX) for cooling compressor oil. For the shell and tube type HX without baffle, by utilizing commercial software ANSYS Fluent, we could verify that the experimental results were relatively well predicted comparing with the CFD results. Furthermore, the cooling performances were calculated for the shell and tube type HX with some cases of baffle numbers and area. The cooling performance of the HX with baffle was higher than that of the HX without baffle. But the effect of baffle numbers was minor. And the cooling performance increases with larger baffle area. But the pressure drop of cooling water increases with increase of baffle numbers and area. From the results of case study, the optimum baffle numbers and area for the high cooling performance could be suggested.

Dynamic response characteristics of cylindrical baffled liquid storage tank to the baffle number

조진래,이선영,송무석 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.12

The goal of current study is to numerically investigate the dynamic response characteristics of cylindrical baffled liquid storage tank, which is subjected to a vertical acceleration at boosting, with respect to the number of baffles. Both the storage tank and baffles are modeled as flexible elastic structures, and the suppression of sloshing-induced dynamic responses by baffles are evaluated in terms of the hydrodynamic pressure, the dynamic displacement and stress. Through the numerical experiments, it has been observed that the introduction of baffles to the partially filled liquid tank remarkably decreases the maximum values of displacement and effective stress at both the bottom plate and baffles. And, the variation of displacement and effective stress is stabilized much faster when baffles are installed and the baffle number increases. Thus, it has been verified that the baffled liquid storage tank can be stably and safely applied to the liquid fuel storage tank for various transport vehicles.

Sloshing suppression by floating baffle

Kang, Hooi-Siang,Md Arif, Ummul Ghafir,Kim, Kyung-Sung,Kim, Moo-Hyun,Liu, Yu-Jie,Lee, Kee-Quen,Wu, Yun-Ta Techno-Press 2019 Ocean systems engineering Vol.9 No.4

Sloshing is a phenomenon which may lead to dynamic stability and damages on the local structure of the tank. Hence, several anti-sloshing devices are introduced in order to reduce the impact pressure and free surface elevation of liquid. A fixed baffle is the most prevailing anti-sloshing mechanism compared to the other methods. However, the additional of the baffle as the internal structure of the LNG tank can lead to frequent damages in long-term usage as this structure absorbs the sloshing loads and thus increases the maintenance cost and downtime. In this paper, a novel type of floating baffle is proposed to suppress the sloshing effect in LNG tank without the need for reconstructing the tank. The sloshing phenomenon in a membrane type LNG tank model was excited under sway motion with 30% and 50% filling condition in the model test. A regular motion by a linear actuator was applied to the tank model at different amplitudes and constant period at 1.1 seconds. Three pressure sensors were installed on the tank wall to measure the impact pressure, and a high-speed camera was utilized to record the sloshing motion. The floater baffle was modeled on the basis of uniform-discretization of domain and tested based on parametric variations. Data of pressure sensors were collected for cases without- and with-floating baffle. The results indicated successful reduction of surface run-up and impulsive pressure by using a floating baffle. The findings are expected to bring significant impacts towards safer sea transportation of LNG.