• Title/Summary/Keyword: Liquid Droplet Behavior

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Numerical Study of Spray Characteristics of n-Heptane in Constant Volume Combustion Chamber under Diesel Engine Conditions (정적연소기를 이용한 디젤 엔진 조건에서 n-Heptane의 분무특성에 관한 수치해석 연구)

  • DAS, SHUBHRA KANTI;LIM, OCKTAECK
    • Transactions of the Korean hydrogen and new energy society
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    • v.27 no.6
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    • pp.727-736
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    • 2016
  • Numerical simulations of n-heptane spray characteristics in a constant volume combustion chamber under diesel engine like conditions with increasing ambient gas density ($14.8-142kg/m^3$) and ambient temperature (800-1000 K) respectively were performed to understand the non-vaporizing and vaporizing spray behavior. The effect of fuel temperature (ranging 273-313 K) on spray characteristics was also simulated. In this simulation, spray modeling was implemented into ANSYS FORTE where the initial spray conditions at the nozzle exit and droplet breakups were determined through nozzle flow model and Kelvin-Helmholtz/Rayleigh-Taylor (KH-RT) model. Simulation results were compared with experimentally obtained spray tip penetration result to examine the accuracy. In case of non-vaporizing condition, simulation results show that with an increment of the magnitude of ambient gas density and pressure, the vapor penetration length, liquid penetration length and droplet mass decreases. On the other hand vapor penetration, liquid penetration and droplet mass increases with the increase of ambient temperature at the vaporizing condition. In case of lower injection pressure, vapor tip penetration and droplet mass are increased with a reduction in fuel temperature under the low ambient temperature and pressure.

Instability of Electrically Driven Polymer Liquid Jets

  • Lee Min-Hyung;Kang Seung-Baik;Park Joo-Hyuk
    • Journal of Mechanical Science and Technology
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    • v.20 no.3
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    • pp.409-417
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    • 2006
  • Polymer nanofibers can be generated by a electrospinning process. The process involves electrically charged jet of polymer solutions evolving from a droplet. The jet stretches in vertical direction due to the difference between charged particle and constant current located at the collector, while the Coulomb and viscoelastic forces start to contribute to radial and azimuthal (torsional) stretching. In this paper, the unstable dynamics of the liquid polymer jet is examined experimentally and theoretically. A complex viscoelastic rheological model has been adopted to analyze the behavior of a charged liquid jet. The model includes complex phenomena of stress relaxation of the liquid jet resulting from the competing force components. The experimental data of the jet paths captured by high-speed videocamera also confirm the similar behavior with the predictions.

Evaluation of Dynamic Wettability of Liquid Zn with Steel Sheets Containing Si and Mn

  • Tanaka, Toshihiro
    • Corrosion Science and Technology
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    • v.9 no.2
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    • pp.87-91
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    • 2010
  • It is pointed out that non-wetting behavior of liquid Zn alloy occurs on high-tensile strength steels, which usually contain Si and Mn. There have been a lot of investigations to improve the above wettability of liquid Zn alloy with steels containing Si and Mn. Although those studies evaluated the wettability qualitatively by observation of the surface of steels galvanized by Zn or exfoliation test of Zn with substrate steels and so on, it is required to evaluate the wettability of liquid Zn with steels by measuring contact angle, work of adhesion, spreading velocity etc. which are usually used to assessment of general wetting behavior. In the present work, we evaluated the wettability of liquid Zn with steels containing Si and Mn by applying a sessile drop method to measure the change in contact angle and diameter of liquid Zn droplet wetted on steels.

Characteristics of Water Droplets in Gasoline Pipe Flow (가솔린 송유관에서의 수액적 거동 특성)

  • Kim, J.H.;Kim, S.G.;Bae, C.;Sheen, D.H.
    • Journal of ILASS-Korea
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    • v.6 no.1
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    • pp.18-24
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    • 2001
  • Liquid fossil fuel contaminated by water can cause trouble in the combustion processes and affect the endurance of a combustion system. Using an optical sensor to monitor the water content instantaneously in a fuel pipeline is an effective means of controlling the fuel quality in a combustion system. In two component liquid flows of oil and water, the flow pattern and characteristics of water droplets are changed with various flow conditions. Additionally, the light scattering of the optical sensor measuring the water content is also dependent on the flow patterns and droplet characteristics. Therefore, it is important to investigate the detailed behavior of water droplets in the pipeline of the fuel transportation system. In this study, the flow patterns and characteristics of water droplets in the turbulent pipe flow of two component liquids of gasoline and water were investigated using optical measurements. The dispersion of water droplets in the gasoline flow was visualized, and the size and velocity distributions of water droplets were simultaneously measured by the phase Doppler technique. The Reynolds number of the gasoline pipe flow varied in the range of $4{\times}10^{4}\;to\;1{\times}10^{3}$, and the water content varied in the range of 50 ppm to 300 ppm. The water droplets were spherical and dispersed homogeneously in all variables of this experiment. The velocity of water droplets was not dependent on the droplet size and the mean velocity of droplets was equal to that of the gasoline flow. The mean diameter of water droplets decreased and the number density increased with the Reynolds number of the gasoline flow.

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An Study on the Spray Structure of Fuel Port Injectors (포트 분사 연료 인젝터의 분무 구조에 관한 연구)

  • Lee, C.S.;Lee, K.H.;Chon, M.S.;Sohn, K.H.;Park, J.S.
    • Journal of ILASS-Korea
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    • v.3 no.3
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    • pp.42-48
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    • 1998
  • This study describes the spray structure of gasoline port injectors by using phase Doppler particle analyzer(PDPA) and particle motion analysis system(PMAS). The characteristics of fuel spray such as the spray penetration, spray angle and breakup processes were obtained by PMAS and the droplet size and mean velocity were measured by PDPA system. Pintle type and two-hole type injectors were used as gasoline port fuel injectors under various injection pressures. The effect of injection pressure on the droplet mean diameter and axial mean velocity of droplet were investigated under the various injection conditions. In addition the comparison of breakup processes for the two types of injectors was also conducted. It Is shown that pintle type injector has smaller droplet size than that of two-hole type injector.

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Wetting Behavior and Evaporation Characteristics of Nanofluid Droplets on Glass Surfaces (나노유체 액적의 젖음거동 및 증발 특성)

  • Shin, Dong-Hwan;Lee, Seong-Hyuk
    • Journal of ILASS-Korea
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    • v.17 no.1
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    • pp.9-13
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    • 2012
  • This study investigates experimentally evaporation characteristics of nanofluid droplets containing 50 nm alumina($Al_2O_3$) particles and the wettability changes on a hydrophilic glass surfaces. From the captured digital images by using a CMOS camera and a magnifying lens, we examined the effect of particle concentration on droplet evaporation rate which can be indirectly deduced from the measured droplet volumes varying with time. In particular, with the use of a digital image analysis technique, the present study measured droplet perimeters and the contact angles to study the wetting dynamics during evaporating process. In addition, we compared the measured total evaporation time with theoretically estimated values. It was found that as the volume fractions of nanofluid increased, the total evaporation time and the initial contact angles decreased, while the droplet perimeters increased.

Characteristics of the Droplet Behavior in the Overlap Region of Twin Spray and in Single Spray (이중분무의 중첩영역과 단일분무에서 액적의 거동 특성)

  • Jung, Ji-Won;Cha, Keun-Jong;Kim, Duck-Jool
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.10
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    • pp.1300-1308
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    • 2000
  • The objectives of this study was to investigate the spray characteristics of single spray and twin spray in the overlap region such as mean axial velocity, mean radial velocity, mean droplet size and probability density function of droplet size. A phase doppler anemometer was used as the measurement system for droplet size and velocity. In case of single spray, injection pressure was varied from 0.2MPa to 0.7MPa. Mean axial velocity, mean radial velocity and droplet size were decreased as the distance below nozzle tip was increased. In case of twin spray, the spray characteristics were measured by varying the distance between two nozzles from 127mm to 155mm. In the overlap region, the boundary of the overlap region was determined by obtaining the distribution of mean axial and radial velocity. Droplet size was increased as the distance from nozzle tip was increased. It was found that the distribution of droplet size for twin spray in the overlap region was different to single spray.

A Study on Droplet Formation from Piezo Inkjet Print Head (피에조 잉크젯 헤드에서 액적 토출 현상에 대한 연구)

  • Oh Se-Young;Lee Jung-Yong;Lee Yu-Seop;Chung Jae-Woo;Wee Sang-Kwon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.30 no.10 s.253
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    • pp.1003-1011
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    • 2006
  • Droplets are ejected onto a substrate through a nozzle by pushing liquids in flow channels of drop-on-demand devices. The behavior of ejection and formation of droplets is investigated to enhance the physical understanding of the hydrodynamics involved in inkjet printing. The free surface phenomenon of a droplet is described using $CFD-ACE^{TM}$ which employs the volume-of-fluid (VOF) method with the piecewise linear interface construction (PLIC). Droplet formation characteristics are analyzed in various flow regimes with different Ohnesorge numbers. The computational results show that the droplet formations are strongly dependent on the physical properties of working fluids and the inlet flow conditions. In addition, the wetting characteristics of working fluids on a nozzle influence the volume and velocity of a droplet produced in the device. This study may provide an insight into how a liquid droplet is formed and ejected in a piezoelectric inkjet printing device.

Analyzing the Spray-to-spray Interaction of GDI Injector Nozzle in the Near-field Using X-ray Phase-Contrast Imaging (X선 위상차 가시화 기법을 이용한 GDI 인젝터 노즐 근방의 분무 간 상호간섭 해석)

  • Bae, Gyuhan;Moon, Seoksu
    • Journal of ILASS-Korea
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    • v.25 no.2
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    • pp.60-67
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    • 2020
  • Despite its benefit in engine thermal efficiency, gasoline-direct-injection (GDI) engines generate substantial particulate matter (PM) emissions compared to conventional port-fuel-injection (PFI) engines. One of the reasons for this is that the spray collapse caused by the spray-to-spray interaction forms the locally rich fuel-air mixture and increases the fuel wall film. Previous studies have investigated the spray collapse phenomenon through the macroscopic observation of spray behavior using laser optical techniques, but it is somewhat difficult to understand the interaction between sprays that is initiated in the near-nozzle region within 10 mm from the nozzle exit. In this study, the spray structure, droplet size and velocity data were obtained using an X-ray imaging technique from the near-nozzle to the downstream of the spray to investigate the spray-to-spray interaction and discuss the effects of spray collapse on local droplet size and velocity distribution. It was found that as the ambient density increases, the spray collapse was promoted due to the intensified spray-to-spray interaction, thereby increasing the local droplet size and velocity from the near-nozzle region as a result of droplet collision/coalescence.

Experimental Study on the Soot Formation Characteristics of Alkane-based Single Fuel Droplet (알케인계 단일 연료 액적의 Soot 생성 특성에 관한 실험적 연구)

  • Lim, Young Chan;Suh, Hyun Kyu
    • Journal of ILASS-Korea
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    • v.22 no.2
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    • pp.80-86
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    • 2017
  • The soot formation characteristics of various alkane-based single fuel droplets were studied in this work. Also, This study was performed to provide the database of the soot behavior and formation of alkane-based single fuel droplet. The experimental conditions were set to 1.0 atm of ambient pressure ($P_{amb}$), 21% of oxygen concentration ($O_2$) and 79% of nitrogen concentration ($N_2$). Combustion and soot formation of single fuel droplet was visualized by visualization system with high speed camera. At the same time, ambient pressure, oxygen concentration and nitrogen concentration were maintained by ambient condition control system. Soot formation characteristics was analyzed and compared on the basis of intensity ratio ($I/I_0$) of background image. The results of toluene fuel droplet showed the largest soot generation. Soot volume fraction ($f_v$) was almost the same under the identical fuel types regardless of various initial droplet diameter ($d_0$) since thermophoretic flux was not much changed under the same ambient conditions.