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  • Title/Summary/Keyword: Droplet Model

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NUMERICAL STUDY OF THE DROPLET EJECTION BEHAVIOR OF NEWTONIAN AND SHEAR-THINNING FLUIDS (뉴튼유체와 전단희석유체의 액적분사 거동에 대한 수치해석적 연구)

  • Kim, E.;Baek, J.
    • Journal of computational fluids engineering
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    • v.17 no.3
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    • pp.33-38
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    • 2012
  • The droplet ejection behavior from drop-on-demand printhead are investigated numerically for Newtonian and shear-thinning fluid. The numerical simulation is performed using a volume-of-fluid model. In this study, we compare the printable range in terms of Z number and pinch-off time for Newtonian and shear-thinning fluids. The printability range are found to be 1.08 Z 12.9 for Newtonian fluid and 0.8 Z 12.9 for shear-thinning fluid. However, air entrainment is observed during merging of primary and satellite droplet within the printability range. The pinch-off time of the shear-thinning fluid is apparently shorter compared to the corresponding Newtonian fluid due to shear-thinning effects and the differences in the pinch-off time is enlarged significantly when the capillary number is larger than 0.5.

Simulation Model for Dissolution of Liquid CO2 Discharged at Intermediate Depth of Ocean (중층심해에 분사된 액체 이산화탄소 용해 예측모델 개발)

  • 김남진;김종보
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.15 no.9
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    • pp.718-726
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    • 2003
  • Carbon dioxide ocean disposal is one of the promising options to reduce carbon dioxide concentration in the atmosphere because the ocean has vast capacity for carbon dioxide sequestration. However, the dissolution rate of liquid carbon dioxide in seawater must be known in advance in order to estimate the amount of carbon dioxide sequestration in the ocean. Therefore, in the present study, calculations of the solubility, the surface concentration and the dissolution behavior of carbon dioxide when liquid carbon dioxide is released at 1,000m and 1,500m in depth are peformed. The results show that the droplet is completely dissolved below 500 m in depth if the carbon dioxide droplet is released both at 1,000m in depth with the initial droplet diameter of 0.011m or less and at 1,500m in depth with the diameter of 0.016 or less. Also, the surface concentration of carbon dioxide droplet with the hydrate film is about 50% of carbon dioxide solubility at 1,500 m in depth and about 60% of carbon dioxide solubility at 1,000 m in depth.

Development and demonstration of an erosion-corrosion damage simulation apparatus (배관 침부식 손상 연속모사 장비 개발 및 실증)

  • Nam, Won Chang;Ryu, Kyung Ha;Kim, Jae Hyoung
    • Corrosion Science and Technology
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    • v.12 no.4
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    • pp.179-184
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    • 2013
  • Pipe wall thinning caused by erosion and corrosion can adversely affect the operation of aged nuclear power plants. Some injured workers owing to pipe rupture has been reported and power reduction caused by unexpected pipe damage has been occurred consistently. Therefore, it is important to develop erosion-corrosion damage prediction model and investigate its mechanisms. Especially, liquid droplet impingement erosion(LDIE) is regarded as the main issue of pipe wall thinning management. To investigate LDIE mechanism with corrosion environment, we developed erosion-corrosion damage simulation apparatus and its capability has been verified through the preliminary damage experiment of 6061-Al alloy. The apparatus design has been based on ASTM standard test method, G73-10, that use high-speed rotator and enable to simulate water hammering and droplet impingement. The preliminary test results showed mass loss of 3.2% in conditions of peripheral speed of 110m/s, droplet size of 1mm-diameter, and accumulated time of 3 hours. In this study, the apparatus design revealed feasibility of LDIE damage simulation and provided possibility of accelerated erosion-corrosion damage test by controlling water chemistry.

Numerical study on pressure drop with moving contact lines of dry slug flow in a hydrophobic minichannel (소수성 미니채널 내 움직이는 접촉선을 가진 액체슬러그의 압력 강하에 대한 수치해석)

  • Jeon, Jun Ho;Park, Su Chung;Yu, Dong In;Kim, Tae Hun;Lee, Yeon Won
    • Journal of the Korean Society of Visualization
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    • v.18 no.3
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    • pp.116-121
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    • 2020
  • In this study, a single-phase analysis of droplet slug with different contact angles was performed based on the visualization of experimental results. Droplet slug - flowing between gases in a hydrophobic mini channel - moves with a triple contact line without a gas liquid film on the wall. The results show that the rotational flow inside the droplet occurred; this was compared and verified with the results of two-phase analysis. The pressure field shows pressure rise at the front and rear ends. The effective length - the section that satisfies the laminar flow condition - became shorter as the droplet velocity increased. The Choi's correlation for the effective length agrees with this analysis results with a slight difference. This difference is judged as the difference in the contact angle of the slug model.

Performance Analysis of Liquid Pintle Thruster Using Quasi-one-dimensional Multi-phase Reaction Flow: Part I Key Sub-model Validation (준 일차원 다상 반응유동 기법을 이용한 케로신/과산화수소 액체 핀틀 추력기 성능해석 연구: Part I. 주요 구성 모델 검증)

  • Kang, Jeongseok;Bok, Janghan;Sung, Hong-Gye;Kwon, Minchan;Heo, JunYoung
    • Journal of the Korean Society of Propulsion Engineers
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    • v.24 no.6
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    • pp.69-77
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    • 2020
  • A quasi one-dimensional multi-phase reaction flow analysis code is developed for the performance analysis of liquid pintle thrusters. Unsteady flow field, droplet evaporation, finite reaction and film cooling models are composed as the major models of the performance analysis. The droplet vaporization takes account of Abramzon's vaporization model, and the combustion employs a flamelet model based on detail chemical reactions. Shine's model is applied for the film cooling calculation. To verify each model, the Sod shock tube, single droplet vaporization, kerosene droplets combustion, and film length are evaluated.

Study of Spray Droplet/Wall Interaction (분무액적과 벽의 상호작용에 대한 연구)

  • 양희천;유홍선;정연태
    • Transactions of the Korean Society of Automotive Engineers
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    • v.6 no.4
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    • pp.86-100
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    • 1998
  • The impingement of the fuel spray on the wall within the combustion chamber in compact high-pressure injection engines and on the intake port wall in port-fuel-inje- ction type engines is unavoidable. It is important to understand the characteristics of impinging spray because it influences on the rate of fuel evaporation and droplet distrib- ution etc. In this study, the numerical study for the characteristics of spray/wall interaction is performed to test the applicability and reliability of spray/wall impingement models. The impingement models used are stick model, reflect model, jet model and Watkins and Park's model. The head of wall-jet eminating radilly outward from the spray impingement site contains a vortex. Small droplets are deflected away from the wall by the stagnation flow field and the gas wall-jet flow. While the larger droplets with correspondingly higher momentum are impinged on the wall surface and them are moved along the wall and are rolled up by wall-jet vortex. Using the Watkins and Park's model the predicted results show the most reasonable trend. The rate of increase of spread and the height of the developing wall-spray is predicted to decrease with increased ambient pressure(gas density).

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Experimental Investigation on the Droplet Entrainment in the Air-Water Horizontal Stratified Flow (물-공기 수평 성층류 유동조건에서 액적이탈 현상에 대한 실험연구)

  • Bae, Byeong Geon;Yun, Byong Jo;Kim, Kyoung Doo;Bae, Byoung Uhn
    • Journal of Energy Engineering
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    • v.24 no.1
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    • pp.114-122
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    • 2015
  • In the high convective gas flow condition, irregular shaped water waves from which droplet entrainment occurs are generated under horizontally stratified two-phase flow condition. KAERI proposed a new mechanistic droplet entrainment model based on the momentum balance equation consisting of the shear stress, surface tension, and gravity forces. However, this model requires correlation or experimental data of several physical parameters related to the wave characteristics. In the present study, we tried to measure the physical parameters such as wave slope, wave hypotenuse length, wave velocity, wave frequency, and wavelength experimentally. For this, an experiment was conducted in the horizontal rectangular channel of which width, height, and length are, respectively, 40 mm, 50 mm, and 4.2 m. In the present test, the working fluids are chosen as air and water. The PIV technique was applied not only to obtain images for phase interface waves but also to measure the velocity field of the water flow. Additionally, we developed the parallel wire conductance probe for the confirmation of wave height from PIV image. Finally, we measured the physical parameters to be used in the validation of new droplet entrainment model.

Reduction of a Numerical Grid Dependency in High-pressure Diesel Injection Simulation Using the Lagrangian-Eulerian CFD Method (Lagrangian-Eulerian 기법을 이용한 고압 디젤 분무 시뮬레이션의 수치해석격자 의존성 저감에 관한 연구)

  • Kim, Sa-Yop;Oh, Yun-Jung;Park, Sung-Wook;Lee, Chang-Sik
    • Transactions of the Korean Society of Automotive Engineers
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    • v.20 no.1
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    • pp.39-45
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    • 2012
  • In the standard CFD code, Lagrangian-Eulerian method is very popular to simulate the liquid spray penetrating into gaseous phase. Though this method can give a simple solution and low computational cost, it have been reported that the Lagrangian spray models have numerical grid dependency, resulting in serious numerical errors. Many researches have shown the grid dependency arise from two sources. The first is due to unaccurate prediction of the droplet-gas relative velocity, and the second is that the probability of binary droplet collision is dependent on the grid resolution. In order to solve the grid dependency problem, the improved spray models are implemented in the KIVA-3V code in this study. For reducing the errors in predicting the relative velocity, the momentum gain from the gaseous phase to liquid particles were resolved according to the gas-jet theory. In addition, the advanced algorithm of the droplet collision modeling which surmounts the grid dependency problem was applied. Then, in order to validate the improved spray model, the computation is compared to the experimental results. By simultaneously regarding the momentum coupling and the droplet collision modeling, successful reduction of the numerical grid dependency could be accomplished in the simulation of the high-pressure injection diesel spray.

Analysis of Effectiveness of Tandem Oil Fences (이중유벽의 유효성에 관한 해석)

  • Han Dong Gi;Lee Choung Mook
    • Journal of the Korean Society for Marine Environment & Energy
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    • v.4 no.1
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    • pp.38-46
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    • 2001
  • To assess the oil-containment effectiveness of tandem oil fences placed in currents, the movement of oil droplets in the fore and aft region of the fences is investigated by experimental and numerical methods. The effect of the flexibility of the fence skirt of single fence on the fence effectiveness is also investigated. Laboratory experiment is conducted to trace the path of a spherical solid particle of equivalent density to an oil droplet which was released in a uniform stream ahead of a model oil fence. Depending upon the releasing position and the flow condition there, it was observed that the particle floated up to the free surface, collided with the fence, or escaped below the fence. By analyzing the droplet trajectories, a numerical method is developed to predict the region ahead of the fore fence where an oil droplet initiating its motion eventually escapes beneath the fence. The effect of the relative sizes of the drafts of the fore and aft fences, the fence separation, and the bottom depth of the sea bed on the effectiveness of tandem fences is investigated using the numerically obtained trajectories of oil droplets.

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Vaporization of Hydrocarbon Fuel Droplet in Supercritical Environments (아임계 및 초임계 탄화수소 연료 액적의 기화 특성 연구)

  • Lee,Gyeong-Jae;Lee,Bong-Su;Kim,Jong-Hyeon;Gu,Ja-Ye
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.31 no.7
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    • pp.85-93
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    • 2003
  • Droplet vaporization at various ambient pressures is studied numerically by formulating one dimensional evaporation model in the mixture of hydrocarbon fuel and air. The ambient pressure ranged from atmospheric conditions to the supercritical conditions. The modified Soave-Redlich-Kwong state equation is used to account for the real gas effects in the high pressure condition. Non-ideal thermodynamic and transport properties at near critical and supercritical conditions are considered. Some computational results are compared with Sato's experimental data for the validation of calculations. The comparison between predictions and experiments showed quite a good agreement. The droplet lifetime increases with increasing pressure at temperature lower than the critical temperature, however, it decreases with increasing pressure at temperature higher than the critical temperature. The solubility of nitrogen can not be neglected in the high pressure and it becomes higher as the temperature and the pressure go up.