• Title/Summary/Keyword: 액적 증발

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Visualization of Breakup and Atomization Processes in Non-evaporating Diesel Sprays (비증발 디젤분무의 분열과 미립화 과정의 가시화)

  • 원영호;김우태
    • Transactions of the Korean Society of Automotive Engineers
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    • v.12 no.1
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    • pp.25-31
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    • 2004
  • Two-dimensional laser visualization methods have been used in the study of breakup and atomization processes of non-evaporating diesel sprays. A single-hole spray injected into a quiescent atmospheric environment was visualized by the LIF(Laser Induced Fluorescence) and scattering technique. The LIF technique could be implemented to take the images which are magnified enough to show the shape of liquid ligaments and small droplets. The spontaneous scattering and fluorescent images of sprays were also taken to investigate the atomization of droplets. In the tip and periphery of a spray. the scattering light is bright and the ratio of fluorescent/scattering intensity is lower. This characteristics indicate the very high number density of small droplets which are well atomized.

Ignition and combustion phenomena of a coal-water slurry droplet (석탄-물 슬러리 액적의 증발 및 점화현상 해석)

  • An, Guk-Yeong;Baek, Seung-Uk;Kim, Gwan-Tae
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.2
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    • pp.632-640
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    • 1996
  • The ignition and combustion characteristics of CWS droplets were investigated in the postflame region generated by a flat burner. The effect of radiation by screen and heating eleements ws taken into account. Also the theoretical claculations considering the temporal temeprature variation have been performed and compared with experimental results. The ignition delays were reduced by the radiation of the screen or heating elements. Therfore the radiation was considered to play some role in predicting the ignition delay.

A Study on Particle Deposition of an Evaporating Colloidal Droplet (콜로이드 액적의 증발에 의한 입자 증착에 관한 연구)

  • Wee Sang-Kwon;Lee Jung-Yong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.30 no.7 s.250
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    • pp.663-670
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    • 2006
  • The presented study aims to investigate the colloidal droplet deposition caused by evaporation of the liquid. In the numerical analysis, the evaporation is carried out by using different evaporation function intended to obtain different shape of solute deposition. In the experiment, the colloidal droplets of different solvents are placed on a glass plate and the surface profiles are measured after drying the solvents of the droplets to investigate the effect of the solvent evaporation on the final deposition profile. Comparing the surface profiles obtained under different conditions, the optimum drying conditions of colloidal droplets are, determined to obtain uniform surface profiles. The numerical results showed that ring-shaped deposition of solute was formed at the edge of the droplet due to the coffee stain effect and the height of the ring was reduced at the lower evaporation rate. The experiments showed that the boiling point of a solvent was critical to the surface uniformity of the deposition profile and the mixture of solvents with different boiling points influenced the uniformity as well.

Effects of Surface Roughness on Evaporation Cooling of Single Water Droplet in Radiative Fields (복사장 내에서 충돌면의 표면조도가 단일액적 증발냉각에 미치는 영향)

  • 유갑종;박철우;장충선
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.16 no.5
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    • pp.467-474
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    • 2004
  • This paper presents the results of an experimental investigation for the effect of radiant heat on the evaporation cooling of water droplet in the process of fire extinguishing. The experiments are mainly focused on the surface temperature, the surface roughness and the droplet diameter. The range of surface temperature is T$_{s}$ =80-14$0^{\circ}C$, surface roughness is R$_{a}$=0.08-0.64 ${\mu}{\textrm}{m}$ and the droplet diameter is $\Phi$=3.0 mm in the radiation. The results show that the evaporation time is shorter for the larger surface roughness and the volume of droplet increased when the surface roughness is 0.64 ${\mu}{\textrm}{m}$ at the surface temperature 127$^{\circ}C$. When the surface roughness is 0.64 ${\mu}{\textrm}{m}$, the heat flux is larger than the surface roughness is 0.08 ${\mu}{\textrm}{m}$ at the surface temperature 81$^{\circ}C$.>.>.

The study of a fire fighting characteristic by a Single Evaporating Droplet in the case of a fire of military enclosure space (군사용 밀폐공간내의 화재시 단일 증발액적에 의한 방재특성 연구)

  • 이진호;방창훈;김정수
    • Journal of the Korea Institute of Military Science and Technology
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    • v.3 no.1
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    • pp.207-217
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    • 2000
  • A fire fighting characteristic by a single evaporating droplet in the case of a fire of military enclosure space was studied experimentally. Transient cooling of solid surface by water droplet evaporation has been investigated through controlled experiments using a heated brass cylinder. Quantitative predictions of droplet evaporation time and in-depth transient temperature distribution in solid have been made. The particular interest was in the removal of thermal energy from the heated cylinder by evaporative cooling. A $10{\mu}1$ single droplet is deposited on a horizontal brass surface with initial temperatures in the range of $90^{\circ}C{\sim}130^{\circ}C.$ The results can be summarized as follows; Evaporating droplet was divided into three different configuration. Evaporation time was predicted as a function of initial surface temperature ($t_c=492.62-6.89T_{s0}+0.0248T_{s0}^2).$ The contact temperature was predicted as a function of initial surface temperature( $T_{i}$=0.94 $T_{s0}$+1.4), The parameter ${\beta}_o$ was predicted as a function of initial surface temperature( ${\beta}_0$ : 0.O0312 $T_{s0}+0.932$)>)>)

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A numerical study on the vaporization of a droplet considering internal circulating flow in the presence of an oscillating flow (진동하는 유동장하에서 내부 순환 유동을 고려한 액적의 증발에 관한 수치적 연구)

  • Ha, Man-Yeong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.5
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    • pp.1700-1716
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    • 1996
  • The two-dimensional, unsteady, laminar conservation equations for mass, momentum, energy and species transport in the gas phase and mass, momentum and energy in the liquid phase are solved simultaneously in spherical coordinates in order to study heating and vaporization of a droplet entrained in the oscillating flow. The numerical solution gives the velocity and temperature distribution in both gas and liquid phase as a function of time. When the gas flow oscillates around an vaporizing droplet, the liquid flow circulates in the clockwise or counterclockwise direction and the temperature distribution in the liquid phase changes its shapes, depending on the gas fow direction. When the gas flow changes its direction of circulating liquid flow is opposite to the gas flow, forming two vortex circulating in the opposite direction. During the heating period, the difference in the maximum and minimum temperature is large, followed by the almost uniform temperature slightly below the boiling temperature. The mass and heat transfer from the droplet depend on the droplet temperature, droplet diameter and the magnitude of relative velocity, giving the droplet lifetime different from the d$^{2}$-law.

The Effect of Microdroplet Shape on the Evaporation (미세액적의 형상이 증발에 미치는 효과)

  • Song, Hyun-Soo;Lee, Yong-Ku;Jin, Song-Wan;Yoo, Jung-Yul
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.6 s.261
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    • pp.558-565
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    • 2007
  • Many studies of microdroplet evaporation from solid surfaces were made with priority given to inkjet printing and dye painting techniques. The objective of these studies is how to evaporate a droplet quickly and uniformly. Also it is necessary to prevent evaporation of a droplet to observe cells in a droplet generated through cell-patterning. In general, an identical volume of a water droplet on hydrophobic surfaces evaporates slower than that on hydrophilic surfaces. In this study, we observe the evaporation process of a droplet on various hydrophobic surfaces and calculated the evaporation rate considering the droplet geometry such as contact angle and height. This study also proposes a new model based on the fact that evaporation mode at the edge of a droplet is different from that at the outer surface of a droplet as the contact angle changes during evaporation. Finally, we reveal the cause fur the increase of evaporation flux and show that the ratio of edge evaporation to total evaporation increases with time.

Unstructured Finite-Volume Analysis of Vaporization Characteristics of Fuel Droplets in Laminar Flow Field (비정렬 유한체적법을 이용한 유동장 내의 연료액적 증발 특성 해석)

  • Kim, T.J.;Kim, Y.M.;Sohn, J.L.
    • Journal of ILASS-Korea
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    • v.5 no.1
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    • pp.13-22
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    • 2000
  • The present study has numerically analyzed the vaporization characteristics of fuel droplets in the high temperature convective flow field. The axisymmetric governing equations for mass, momentum, energy, and species are solved by an iterative and implicite unstructured finite-volume method. The moving boundary due to vaporization is handled by the deformable unstructured grid technique. The pressure-velocity coupling in the density-variable flows is treated by the SIMPLEC algorithm. In terms of the matrix solver, Bi-CGSTAB is employed for the numerically efficient and stable convergence. The n-decane is used as a liquid fuel and the initial droplet temperature is 300K. Computations are performed for the nonevaporating and evaporating droplets with the relative interphase velocity(25m/s). The unsteady vaporization process has been simulated up to the nondimensional time, 25. Numerical results indicate that the mathematical model developed in this study succesfully simulates the main features of the droplet vaporization process in the convective environment.

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