• Title, Summary, Keyword: bubble-point

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Modeling of Mesh Screen for Use in Surface Tension Tank Using Flow-3d Software (Flow-3d를 이용한 표면장력 탱크용 메시 스크린 모델링)

  • Kim, Hyuntak;Lim, Sang Hyuk;Yoon, Hosung;Park, Jeong-Bae;Kwon, Sejin
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.984-990
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    • 2017
  • Mesh screen modeling and liquid propellant discharge simulation of surface tension tank were performed using commercial CFD software Flow-3d. $350{\times}2600$, $400{\times}3000$ and $510{\times}3600$ DTW mesh screen were modeled using macroscopic porous media model. Porosity, capillary pressure, and drag coefficient were assigned for each mesh screen model, and bubble point simulations were performed. The mesh screen model was validated with the experimental data. Based on the screen modeling, liquid propellant discharge simulation from PMD tank was performed. NTO was assigned as the liquid propellant, and void was set to flow into the tank inlet to achieve an initial volume flow rate of liquid propellant in $3{\times}10^{-3}g$ acceleration condition. The intial flow pressure drop through the mesh screen was approximately 270 Pa, and the pressure drop increased with time. Liquid propellant discharge was sustained until the flow pressure drop reached approximately 630 Pa, which was near the estimated bubble point value of the screen model.

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Large-Scale Structure of Leading-Edge Separation Bbubble with Local Forcing (국소교란이 가해지는 박리기포의 대형구조)

  • 김유익;성형진
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.4
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    • pp.1134-1147
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    • 1995
  • POD (proper orthogonal decomposition) is applied to turbulent leading-edge separation bubble to extract coherent structures. A two-dimensional leading-edge separation bubble is simulated by discrete-vortex method, where a time-dependent source forcing is incorporated. Based on the wealth of numerical data, POD is applied in a range of the forcing amplitude ( $A_{o}$ = 0, 0.5, 1.0 and 1.5) and forcing frequency (0 .leq. $f_{F}$H/ $U_{\infty}$.leq. 0.3). It is demonstrated that the structures of POD have noticeable changes with local forcings. In an effort to investigate the mechanism of decreasing reattachment length, dynamic behaviors of the expansion coefficients and contributions of the eigenfunctions of POD are scrutinized. As the forcing amplitude increases, the large-scale vortex structures are formed near the forcing amplitude increases, the large-scale vortex structures are formed near the separation point and the flow structures become more organized and more regular, accompanying with the reduction of reattachment length. By further inverstigation of POD global entropy, it is seen that the reattachment length is closely linked to the degree of organization of the flow structures.es.s.

Gas holdup and hydrodynamic flow regime transition in bubble columns

  • Kim, Jun Young;Kim, Bongjun;Nho, Nam-Sun;Go, Kang-Seok;Kim, Woohyun;Bae, Jong Wook;Jeong, Sung Woo;Epstein, Norman;Lee, Dong Hyun
    • Journal of Industrial and Engineering Chemistry
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    • v.56
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    • pp.450-462
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    • 2017
  • The homogeneous-to-heterogeneous flow regime transition point dependence on gas and liquid properties was investigated in a semi-cylindrical bubble column of 1.8 m height and 0.21 m inner diameter operating as a semi-batch system. He, air, and $CO_2$ gases were injected at superficial gas velocities of up to 239 mm/s. The batch liquids included water, aqueous ethanol solutions, and aqueous glycerol solutions, all with a gas-free liquid height settled at 1 m. When the gas density increased, the gas holdup increased at all superficial gas velocities, delaying the flow regime transition. The gas holdups in the liquid mixtures were higher than those for tap water. The transition gas holdup for the ethanol solutions increased to a sharp maximum and then decreased as the surface tension increased. Also, the glycerol solutions showed similar behavior with respect to increasing liquid viscosity, but with a shallower maximum. The transition gas holdup was empirically correlated as a function of the gas density, surface tension, and liquid viscosity, employing dimensional constants. The measured transition gas holdups for liquid mixtures, as well as some data from the literature, were fitted by the correlation.

A Study on the Formation Mechanism of Discontinuities in $CO_2$ Laser Fusion Zone of Fe-Co-Ni Sintered Segment and Carbon Steel (Pe-Co-Ni 분말 소결 금속과 탄소강의 이종재료간 레이저 용접부의 결함형성기구 연구)

  • 신민효;김태웅;박희동;이창희
    • Journal of Welding and Joining
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    • v.21 no.3
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    • pp.58-67
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    • 2003
  • In this study, the formation mechanism of discontinuities in the laser fusion zone of diamond saw blade was investigated. $CO_2$ laser weldings were conducted along the butt between Fe base sintered tip and carbon steel shank with sets of variable welding parameters. The effect of heat input on irregular humps, outer cavity, inner cavity and bond strengh was evaluated. The optimum heat input to have a proper humps was in the range of 10.4~$17.6kJm_{-1}$. With increasing heat input, both outer and inner cavities were reduced. The outer cavity was caused by insufficient refill of keyhole, while inner cavity was caused by trapping of bubble in molten metal. The bubble came from sintered tip and intensive vaporization at bottom tip of the keyhole. A gas formation and low melting point element vaporization were not occurred during welding. We could not find any relationship between bond strength and amount of discontinuities. Because the fracture were occurred in not only sintered tip but also carbon steel shank due to hardness distributions.

Performance Increase for a 2 kW Open Cathode Type Fuel Cell Using Temperature/Humidity Control (2 kW급 개방 캐소드형 연료전지 출력 향상을 위한 온습도 제어)

  • YUAN, WEIWEI;CHOI, MIHWA;YANG, SEUGRAN;KIM, YOUNG-BAE
    • Transactions of the Korean hydrogen and new energy society
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    • v.28 no.4
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    • pp.369-376
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    • 2017
  • Temperature and humidity regulations of an open-cathode PEM fuel cell with balance of plant (BOP) are developed in this study. The axial fan, a bubble humidifier, set of solenoid valves and a controller are used to perform temperature and humidity control simultaneously. A fuzzy controller is designed, and it shows its superiority in real-time controlling for strong non-linear dynamical fuel cell system. The axial fan speed is used for temperature control and solenoid valve on/off signal of the bubble humidifier is used for humidity control. The axial fan speed is controlled to keep the fuel cell temperature within the desired point. Meanwhile, the bubble humidifier is utilized to moisture hydrogen to manage the water content of membrane. The results show that the proposed fuzzy controller effectively increases the output power of 10% for a PEM fuel cell.

Simulations of fiber spinning and film blowing based on a molecular/continuum model for flow-induced crystallization

  • McHugh, Anthony J.;Doufas, A.K.
    • Korea-Australia Rheology Journal
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    • v.13 no.1
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    • pp.1-12
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    • 2001
  • This paper describes the application of our recently developed two-phase model for flow-induced crystallization (FIC) to the simulation of fiber spinning and film blowing. 1-D and 2-D simulations of fiber spinning include the combined effects of (FIC), viscoelasticity, filament cooling, air drag, inertia, surface tension and gravity and the process dynamics are modeled from the spinneret to the take-up roll device (below the freeze point). 1-D model fits and predictions are in very good quantitative agreement with high- and low-speed spinline data for both nylon and PET systems. Necking and the associated extensional softening are also predicted. Consistent with experimental observations, the 2-D model also predicts a skin-core structure at low and intermediate spin speeds, with the stress, chain extension and crystallinity being highest at the surface. Film blowing is simulated using a "quasi-cylindrical" approximation for the momentum equations, and simulations include the combined effects of flow-induced crystallization, viscoelasticity, and bubble cooling. The effects of inflation pressure, melt extrusion temperature and take-up ratio on the bubble shape are predicted to be in agreement with experimental observations, and the location of the frost line is predicted naturally as a consequence of flow-induced crystallization. An important feature of our FIC model is the ability to predict stresses at the freeze point in fiber spinning and the frost line in film blowing, both of which are related to the physical and mechanical properties of the final product.l product.

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Study on the Convergency Improvement Method for the Saturation-Property Calculation of Multi-Component Hydrocarbon Systems (다성분 탄화수소혼합물 포화물성해석 수렴도 향상 연구)

  • Shin, Chang-Hoon;An, Seung-Hee;Lee, Jeong-Hwan;Sung, Won-Mo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.34 no.10
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    • pp.947-955
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    • 2010
  • Most oil and gas reservoirs, which have some light hydrocarbon components, show sensitive phase behavior in response to changes in the composition of the internal fluid. When evaluating and developing plans for oil and gas fields, flash calculation, PVT analysis, and saturation-property calculation are necessary for analyzing reservoir characteristics and pipeline flows. In general, the determination of saturation properties such as dew point and bubble point is considered a difficult task because of the poor convergence of the calculation methods. In this study, several new initial-value-guessing methods and root-finding methods are proposed; parametric analysis were carried out to verify the improvement in convergence. Finally, these new ideas and methods were successfully applied to the new GUI based multi-phase behavior simulator.

Aeroacoustic Noise Generation in Unsteady Laminar Boundary-layer Separation (비정상 층류 경계층 박리에 의한 유동 소음)

  • Choi, Hyo-Won;Moon, Young-J.
    • Proceedings of the KSME Conference
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    • pp.300-305
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    • 2001
  • The unsteady flow structure and the related noise generation, which are caused by the separation of a two-dimensional, incompressible, laminar boundary-layer on the flat plate under the influence of local adverse pressure gradient, are numerically examined. The characteristic lines of the wall pressure are examined to understand the unsteady behavior of vortex shedding near the reattachment point of the separation bubble. Also, the generation and propagation of the vortex-induced noise in the separated boundary-layer are calculated by the method of computational aero-acoustics (CAA), and the effects of Reynolds number, Mach number and the strength of the adverse pressure gradient on the unsteady flow and noise characteristics are examined.

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Evaluation and modelling of the separation of anthracite in the hindered-settling column

  • Kim, Jeong-Yun;Cho, Hee-Chan
    • 한국지구물리탐사학회:학술대회논문집
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    • pp.611-617
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    • 2003
  • This study was performed to develop the method for producing industrial coal sources by cleaning Korean anthracite. Laboratory hindered-settling separation column was set and three coal samples were used for tests. Tests were conducted to evaluate the effects of the major operating variables, teeter water flow rate and relative column pressure (set point). Additional tests were performed to elevate the yield and properties of the products using air bubble injecting process. In results, nice products were obtained with high teeter water flow rate and air bubble injection. Also, model of continuous hindered-settling separation process was established to assist the evaluation of the equipment and several operating variables, such as dispersion, teeter water flow rate, feeding rate, etc.

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