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  • Title/Summary/Keyword: Droplet Model

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An experimental study on swirling spray flame structure by air-blast nozzle (기류분사 노즐에 의한 선회 분무 화염의 구조에 관한 실험적 연구)

  • O, Sang-Heon;Baek, Min-Su;Kim, Dong-Il
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.4
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    • pp.473-485
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    • 1997
  • Detailed experimental study has been made of air blast kerosene spray flames with and without swirl in combustion air flow. Phase-Doppler detect technique is used to measure Sauter mean diameter, axial component mean and rms velocity, size-velocity correlation, and number density. These measurements are obtained for both nonreacting and reacting cases under several stable flame conditions. The results show that the introduction of swirl to the combustion air modifies the spatial distribution of droplet size, velocity, and number density, and thus alters the flame structure. However, due to the weak swirl intensity, the overall structure of swirling flames are essentially same as that of nonswirling flames. Physical model of structure of air blast atomized spray flames is projected to show that spray flames are composed of three distinct regions: the two-phase mixture region, the main reaction and the intermittent combustion region. Near the atomizer, two phase mixture of droplet and air is formed in the core region. This dense spray region is characterized by high droplet number density and the strong convective effect. There follows the main combustion region where the main flame penetrates within the spray boundary. Main reaction region of these flames are governed by internal group combustion mode. Finally there exists the intermittent combustion region where local group burning or isolated droplet burning occurs.

Estimation of FDS Prediction Performance on the Operation of Water-Mist (미세물분무 작동에 대한 FDS 예측 성능 평가)

  • Ko, Gwon Hyun
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.15 no.8
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    • pp.4809-4814
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    • 2014
  • The aim of the present study was to estimate the prediction performance of a FDS (Fire Dynamic Simulator) to simulate the fire behaviors and suppression characteristics by operating a water-mist. Rosin-Rammler/log-normal distribution function was used to determine the initial droplet distribution of water-mist and the effects of its model constant were considered. In addition, the simulation models were validated by a comparison of the predicted fire suppression characteristics with water-mist injection pressures to the previous experiments, and the thermal flow behaviors and gaseous concentration variations were analyzed. The results showed that water-mists with the same mean diameter were affected by the characteristics of the droplet size distribution, which have different size and velocity distributions at the downstream location. The fire simulations conducted in this study determine the initial droplet size distribution tuned to the base of the spray characteristics measured by previous experiments. The simulation results showed good agreement with the previous measurements for temperature variations and fire suppression characteristics. In addition, it was confirmed that the FDS simulation with a water-mist operation supplies useful details on estimations of the thermal flow fields and gaseous concentration under water mist operation conditions.

Modeling and Experimental Verification on Static Landing Accuracy of Droplets from Magnetostrictive Inkjet Head (자기변형잉크젯헤드에서 토출된 액적의 정적 착지정확도 모델링 및 실험적 검증)

  • Yoo, Eun Ju;Park, Young Woo
    • Journal of the Korean Society for Precision Engineering
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    • v.30 no.1
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    • pp.77-84
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    • 2013
  • Most research on the inkjet printing technology has focused on the development of inkjet head itself, and of process, not on the landing accuracy of the droplets to a target. Thus, this paper presents the modeling and experimental verification on the static landing accuracy and precision of the droplets from the magnetostrictive inkjet head. A simple model based on the angle deviation of a nozzle tip and on a distance to a substrate is considered, assuming that there is no ambient effect. The angle deviation of the nozzle tip is determined by using its digital image with the aid of a pixel calculation program, and the distance to the substrate is set to 1 mm. Three experiments have planned and preformed. The first experiment is to collect the initial data for the landing distribution of the droplets. The second experiment is to collect the repeatability data of the stage used. Then, these data are used to rederive the equation for the final landing position of the droplet. The final experiment is to verify the equation and to show the calibration results. The respective landing accuracy of the droplet after calibration on the x-axis and on y axis has improved from 338.51μm and 133.63μm to 7.06μm and 13.11μm. The respective percent improvement on the x-axis and on y axis reaches about 98 and about 90. The respective landing precision of the droplet after calibration on the x-axis and on y axis has improved from ±182.6μm and ±182.88μm to ±24.64μm and ±42.76μm. The respective percent improvement on the x-axis and on y axis reaches about 87 and about 77.

Controlling Factors of Open-Loop Combustion Response to Acoustic Pressures in Liquid Propellant Rocket Engine (강한 압력파동에 구속된 액체 추진제 연소응답의 지배인자)

  • Yoon Woongsup;Lee Gilyong
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2004.10a
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    • pp.267-273
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    • 2004
  • This paper targets to define controlling factors of pressure-coupled combustion response and estimate their effects on droplet evaporation process. Dynamic characteristics of hydrocarbon propellant vaporization perturbed by acoustic pressure are numerically simulated and analyzed. 1-D droplet model including phase equilibrium between two phases is applied and acoustic wave is expressed by harmonic function. Effects of various design factors and acoustic pressure on combustion response are investigated with parametric studies. Results show that driving frequency of acoustic perturbation and ambient pressure have important roles in determining magnitude and phase of combustion response. On the other hand, other parameters such as gas temperature, initial droplet size and temperature, and amplitude of acoustic wave cause only minor changes to magnitude of combustion response. Resultant changes in phase of heat of vaporization and thermal wave in droplet highly influence magnitude and phase of combustion response.

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Experimental Investigation and Modeling of the Specific Enthalpy Distribution in a Spray Cone

  • Ellendt, N.;Uhlenwinkel, V.
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09a
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    • pp.58-59
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    • 2006
  • In Spray Forming, specific enthalpy is a key parameter in the deposition process as it influences the thermal condition of the impinging droplets as well as that of the deposit surface. An empirical model for the distribution of specific enthalpy in the spray cone was developed as an easy to handle alternative to numerical models with which the descriptive partial differential equations are solved numerically. The model results were compared with the experimental data to validate its applicability.

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Numerical Study on the Evaporation Characteristics of Biocrude-oil Produced by Fast Pyrolysis (급속열분해를 통하여 생산된 바이오오일 액적의 증발 특성에 관한 수치해석적 연구)

  • Choi, Sang Kyu;Choi, Yeon Seok;Kim, Seock Joon;Han, So Young
    • Applied Chemistry for Engineering
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    • v.27 no.6
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    • pp.646-652
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    • 2016
  • Biomass is regarded as one of the promising energy sources to deal with the depletion of fossil fuels and the global warming issue. Biocrude-oil can be produced through the fast pyrolysis of biomass feedstocks such as wood, crops, agricultural and forestry residues. It has significantly higher viscosity than that of conventional petroleum fuel and contains solid residues, which can lower the spray and atomization characteristics when applied to the burner. In addition, biocrude-oil consists of hundreds of chemical species derived from cellulose, hemicellulose and lignin, and evaporation characteristics of the biocrude-oil droplet are distinct from the conventional fuels. In the present study, a numerical study was performed to investigate the evaporation characteristics of biocrude-oil droplet using a simplified composition of the model biocrude-oil which consists of acetic acid, levoglucosan, phenol, and water. The evaporation characteristics of droplets were compared at various surrounding air temperatures, initial droplet diameters, and ethanol mixing ratios. The evaporation time becomes shorter with increasing air temperature, and it is much sensitive to the air temperature particularly in low temperature ranges. It was also found that the biocrude-oil droplet evaporates faster in cases of the smaller initial droplet diameter and larger ethanol mixing ratio.

Theoretical Model of Coaxial Twin-Fluid Spray In a Liquid Rocket Combustor (연소실 내 동축형 2-유체 분무의 이론적 모델)

  • 조용호;윤웅섭
    • Journal of the Korean Society of Propulsion Engineers
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    • v.6 no.2
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    • pp.37-44
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    • 2002
  • A theoretical study of spray and combustion characteristics due to coaxial twin-fluid injection is conducted to investigate the effects of liquid jet property, droplet size, contact length and liquid jet velocity. Model is properly validated with measurements and shows good agreement. Prediction of jet contact length, droplet size, liquid jet velocity reflects genuine features of coaxial injection in physical and practical aspects. Both the jet contact length and tile droplet size are reduced in a linear manner with an increase of injector diameter. Cross sectional area of liquid intact core is reduced with augmented jet splitting rate, thus the jet is accelerated to maintain the mass continuity and with an assistant of momentum diffusion by burnt gas.

Energy-saving potential of cross-flow membrane emulsification by ceramic tube membrane with inserted cross-section reducers

  • Albert, K.;Vatai, Gy.;Giorno, L.;Koris, A.
    • Membrane and Water Treatment
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    • v.7 no.3
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    • pp.175-191
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    • 2016
  • In this work, oil-in-water emulsions (O/W) were prepared successfully by membrane emulsification with 0.5μm pore size membrane. Sunflower oil was emulsified in aqueous Tween80 solution with a simple crossflow apparatus equipped with ceramic tube membrane. In order to increase the shear-stress near the membrane wall, a helical-shaped reducer was installed within the lumen side of the tube membrane. This method allows the reduction of continuous phase flow and the increase of dispersed phase flux, for cost effective production. Results were compared with the conventional cross-flow membrane emulsification method. Monodisperse O/W emulsions were obtained using tubular membrane with droplet size in the range 3.34.6μm corresponded to the membrane pore diameter of 0.5μm. The final aim of this study is to obtain O/W emulsions by simple membrane emulsification method without reducer and compare the results obtained by membrane equipped with helix shaped reducer. To indicate the results statistical methods, 3p type full factorial experimental designs were evaluated, using software called STATISTICA. For prediction of the flux, droplet size and PDI a mathematical model was set up which can describe well the dependent variables in the studied range, namely the run of the flux and the mean droplet diameter and the effects of operating parameters. The results suggested that polynomial model is adequate for representation of selected responses.

Effect of the Statistical Droplet Parcel on Numerical Simulation of Sprinkler Spray (스프링클러 분무 해석에 영향을 미치는 통계적액적군집의 영향)

  • Kim, Sung-Chan;Lee, Sang-Woo;Park, Won-Ju
    • Proceedings of the Korea Institute of Fire Science and Engineering Conference
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    • 2008.11a
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    • pp.363-370
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    • 2008
  • The present study has been performed to investigate the effect of statistical number of droplets on the simulation of the sprinkler spray using fire field model. In order to simulate the sprinkler spray characteristics, the present study uses NIST Fire Dynamics Simulator version 5.2. A group of Lagrangian particle with similar droplet characteristics, such as diameter, velocity, temperature and so on, is represented by parcel concept to decrease the total number of droplets tracked in the simulation. The present study introduces a new parameter to represent the ratio between real number of droplets and computational parcels. The dependency of the number of parcels on the fire suppression characteristics and spray patterns is quantitatively examined for different ratio between the real number of droplets and computational parcels.

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A study on ice-slurry production by water spray (수분무에 의한 아이스 슬러리 생성에 관한 연구)

  • Kim, B.S.;Lee, Y.P.;Yoon, S.Y.;Lee, J.H.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.9 no.2
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    • pp.134-143
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    • 1997
  • A theoretical and experimental study has been performed to investigate the characteristics of ice-slurry product. By diffusion-controlled model, the possibility of ice slurry has been theoretically anticipated. The water vapor evaporated from the surface of droplets is extracted continuously from the chamber by a vacuum pump. The droplet diameter was measured by silion immersed method. The ice slurry has been obtained by spraying droplets of ethylene-glycol aqueous solution in the chamber where pressure is maintained under the triple point of water. The droplet of which the diameter is 300μm, and the initial temperature is 20C, was changed into ice particle within the chamber of which the height is 1.33m.

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