• 대한기계학회논문집B
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• 제29권4호
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• pp.485-494
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• 2005

For the extensive investigation of local heat/mass transfer on the near-tip surface of turbine blade, experiments were conducted in a low speed stationary annular cascade. The turbine test section has a single stage composed of sixteen guide vanes and blades. The chord length and the height of the tested blade are 150 mm and about 125 mm, respectively. The blade has flat tip geometry and the mean tip clearance is about $2.5{\%}$ of the blade chord. Detailed mass transfer coefficient on the blade near-tip surface was obtained using a naphthalene sublimation technique. The inlet flow Reynolds number based on chord length and incoming flow velocity is changed from $1.0{\times}10^{5}\;to\;2.3{\times}10^{5}.$ Extremely complex heat transfer characteristics are observed on the blade surface due, to complicated flow patterns, such as flow acceleration, laminarization, transition, separation bubble and tip leakage flow. Especially, the suction side surface of the blade has higher heat/mass transfer coefficients and more complex distribution than the pressure side surface, which is related to the leakage flow. For all the tested Reynolds numbers, the heat/mass transfer characteristics on the turbine blade are the similar. The overall averaged $Sh_{c}$ values are proportional to $Re_{c}^{0.5}$ on the stagnation region and the laminar flow region such as the pressure side surface. However, since the flow is fully turbulent in the near-tip region, the heat/mass transfer coefficients are proportional to $Re_{c}^{0.8}.$

• 설비공학논문집
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• 제18권1호
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• pp.55-65
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• 2006

The air and water flow distribution are experimentally studied for a round header - flat tube geometry simulating a parallel flow heat exchanger. The number of branch flat tube is thirty. The effects of tube outlet direction, tube protrusion depth as well as mass flux, and quality are investigated. The flow at the header inlet is identified as annular. For the downward flow configuration, the water flow distribution is significantly affected by the tube protrusion depth. For flush-mounted configuration, most of the water flows through frontal part of the header. As the protrusion depth increases, more water is forced to the rear part of the header. The effect of mass flux or quality is qualitatively the same as that of the protrusion depth. Increase of the mass flux or quality forces the water to rear part of the header. For the upward flow configuration, however, most of the water flows through rear part of the header. The protrusion depth, mass flux, or quality does not significantly alter the flow pattern. Possible explanations are provided based on the flow visualization results. Negligible difference on the water flow distribution was observed between the parallel and the reverse flow configuration.

• Journal of Biosystems Engineering
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• 제20권1호
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• pp.58-65
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• 1995

A numerical study for a two dimensional multi-jet with crossflow of the spent fluid has been carried out. Three different distributions of mass-flow rate at 5 jet exits were assumed to see their effects upon the flow characteristics, especially in the jet-flow region. For each distribution, various Reynolds numbers ranging from laminar to turbulent flows were considered. Calculations drew the following items as conclusion. 1) The development of the free jets issued from downstream jets was hindered by the crossflow formed due to jets. Consequently, the free jet was developed into the channel flow without any evident symptom of impingement jet flow characteristics 2) The crossflow induced the pressure gradient along the cross section of jet exits and the value of the pressure gradient increased as going downstream. The crossflow generated also the turbulent kinetic energy as it collied with the downstream jets. 3) The skin friction coefficient along the impingement plate was affected more by the distribution of mass flow rate at jet exits rather than by the Reynolds number. The skin friction coefficient was inversely proportional to the square root of the Reynolds number, regardless of flow regime when a fully developed flow was formed in the jet flow region. 4) The distribution of the skin friction coefficient along the impingement plate was found to be controlled by adjusting the distribution of mass flow rate at jet exits.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2267-2272
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• 2007

The present study investigates the two dimensional flow and heat/mass transfer characteristics of wavy duct with various corrugation angles. For the heat/mass transfer coefficients, a naphthalene sublimation technique is used. Numerical analysis and wall pressure measurement show detailed two dimensional flow features. The corrugation angles change from 145$^{\circ}$ to 100$^{\circ}$. The operating Reynolds numbers based on the duct hydraulic diameter vary from 700 to 3,000. The duct aspect ratio maintains 7.3. On the pressure wall, strong flow mixing enhances heat/mass transfer coefficients at the front position. In addition, the rear side of pressure wall, the near of peak, is affected by the acceleration and the shedding of main flow. On the suction wall, however, flow separation and reattachment lead to the valley and the peak of heat/mass transfer coefficient. Also, highly increasing boundary layer at the suction wall affects the decrease of heat/masst transfer. As decreasing corrugation angles, the spanwise average Sherwood number increases and the peak or the valley positions of the local Sherwood number are varied.

• 제어로봇시스템학회논문지
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• 제15권3호
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• pp.330-336
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• 2009

This paper studies on the new control algorithm for the mass-flow stabilization in strip head part of a hot strip mill. A new strip tension model in the strip head part is derived using the current deviation of two neighboring stands. The current deviation means a difference between a measured current and a lock-on current, where the lock-on current is set up when a strip tension or a looper angle reaches each target value or time is about 0.4sec, respectively. On the basis of the tension calculation model, a mill velocity of a backward stand is controlled to stabilize a strip mass-flow by PI control algorithm. Therefore, the mass-flow control for strip head part is executed from a metal-in time into a foreward stand till the looper works normally. It is known by the results of a computer simulation and an experiment that the proposed control algorithm is very effective in stabilizing the mass flow of the strip head part.

• 한국산학기술학회논문지
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• 제4권2호
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• pp.63-70
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• 2003

본 논문에서는 반도체 제조장비의 핵심 부품 중에 하나인 질량유량제어기(MFC, Mass Flow Controller)클 설계하고 구현하였다 Microchip社의 마이크로콘트롤러(Microcontroller) PIC 16F876을 사용하여 개발된 MFC는 여러가지 문제점을 가진 아날로그(Analog) 방식의 MFC와 고가의 DSP(Digital Signal Processor) 및 고분해능의 AD변환기(Analog to Digital Convertor)를 사용하는 디지털 MFC의 장점을 혼합한 하이브리드형(Hybrid-Type)이다. 본 논문에서 개발된 MFC는 크게 센서부(Sensor Unit), 제어부(Control Unit), 구동기부(Actuator Unit)로 구성되었으며, 성능향상을 위한 자동보정(Automatic Calibration) 알고리즘과 표준테이블(Reference Table) 방식을 사용하였다.

• Journal of Mechanical Science and Technology
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• 제18권8호
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• pp.1435-1450
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• 2004

Experimental data are presented which describe the effects of a combustor-level high free-stream turbulence on the near-wall flow structure and heat/mass transfer on the endwall of a linear high-turning turbine rotor cascade. The end wall flow structure is visualized by employing the partial- and total-coverage oil-film technique, and heat/mass transfer rate is measured by the naphthalene sublimation method. A turbulence generator is designed to provide a highly-turbulent flow which has free-stream turbulence intensity and integral length scale of 14.7% and 80mm, respectively, at the cascade entrance. The surface flow visualizations show that the high free-stream turbulence has little effect on the attachment line, but alters the separation line noticeably. Under high free-stream turbulence, the incoming near-wall flow upstream of the adjacent separation lines collides more obliquely with the suction surface. A weaker lift-up force arising from this more oblique collision results in the narrower suction-side corner vortex area in the high turbulence case. The high free-stream turbulence enhances the heat/mass transfer in the central area of the turbine passage, but only a slight augmentation is found in the end wall regions adjacent to the leading and trailing edges. Therefore, the high free-stream turbulence makes the end wall heat load more uniform. It is also observed that the heat/mass transfers along the locus of the pressure-side leg of the leading-edge horseshoe vortex and along the suction-side corner are influenced most strongly by the high free-stream turbulence. In this study, the end wall surface is classified into seven different regions based on the local heat/mass transfer distribution, and the effects of the high free-stream turbulence on the local heat/mass transfer in each region are discussed in detail.

• 동력기계공학회지
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• 제17권6호
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• pp.54-62
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• 2013

A numerical analysis is performed to evaluate mass flow balance in the heat exchanger for the dehumidifier. To improve the mass flow balance for maximum heat transfer performance, inlet, outlet and baffle are changed. Mass flow balance is evaluated by non-uniformity of flow which is the same concept with the standard deviation. Usually, there will occur many paths between the inlet and the outlet, however, it will follow shortest and low resistance ways. The uniform distribution of flow is numerically analyzed for several types of heat exchangers. Making the shortest way between the inlet and the outlet is most important factor. Two types of heat exchangers are installed in the dehumidifier and 4 cases of Type A heat exchangers and 3 cases of Type B heat exchangers are evaluated and optimized. The result of this research is applied to design heat exchanger for commercial dehumidifiers.

• 대한기계학회논문집B
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• 제37권5호
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• pp.503-511
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• 2013

연료전지 시스템에서 공급기체 가습은 연료전지 성능효율과 전해질막 수명 향상 측면에서 중요하다. 판형 막 가습기는 일반적으로 유동 방향에 따라 직교류와 대향류로 구분되고 판과 막 사이에서 고온 다습한 공기와 저온 건조한 공기의 열 및 물질전달이 이루어진다. 본 연구에서는 현열 및 잠열 ${\varepsilon}$-NTU 법을 이용하여 입구 온도와 유량 변화에 따른 열 및 물질전달 성능 변화를 유동 방향에 따라 비교하였다. 이를 통하여 저유량 일 때 대향류는 직교류 보다 열 및 물질전달 성능이 높은 것을 알 수 있었고 유량이 증가함에 따라 성능 차이가 감소되는 것을 확인할 수 있었다. 그리고 입구온도가 증가함에 따라 열전달 성능 변화는 작은 반면 물질전달 성능 변화는 비선형으로 크게 감소되는 결과를 얻었다.

• 설비공학논문집
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• 제12권1호
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• pp.102-111
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• 2000

A numerical model which simulates the simultaneous heat and mass transfer within a vertical tube GAX absorber was developed. The ammonia vapor and the solution liquid are in counter-current flow, and the hydronic fluid flows counter to the solution liquid. The film thickness and the velocity distribution of the liquid film were obtained by matching the shear stress at the liquid-vapor interface. Two-dimensional diffusion and energy equations were solved in the liquid film to give the temperature and concentration, and a modified Colburn-Drew analysis was used for the vapor phase to determine the heat and mass fluxes at the liquid-vapor interface. The model was applied to a GAX absorber to investigate the absorption rates, temperature and concentration profiles, and mass flow rates of liquid and vapor phases. It was shown that the mass flux of water was negligible compared with that of ammonia except the region near the liquid inlet. Ammonia absorption rate increases rapidly near the liquid inlet and decrease slowly. Both the absorption rate of ammonia vapor and the desorption rate of water near the liquid inlet increase as the vapor mass flow rate increases, but the mass fluxes of the ammonia and the water near the liquid outlet decrease as the mass flow rate of the vapor increases.