• Title/Summary/Keyword: Droplet diameter

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A Study on the Droplet Behavior Impacting on an Orifice (오리피스와 충돌하는 액적 거동에 관한 연구)

  • D.H., Seo;D.J., Lee;H.B., Lee;B.S., Kang
    • Journal of ILASS-Korea
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    • v.27 no.4
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    • pp.188-194
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    • 2022
  • In this study, the behavior of water droplet impacting on a thin horizontal orifice was investigated. The impact behavior modes, transition velocities and diameters of daughter droplets were analyzed by changing the droplet velocity, orifice diameter and orifice thickness. Four typical modes of impacting droplet on an orifice were observed. The single-droplet and double-droplet transition velocities increased with increasing the orifice thickness and decreased with increasing the orifice diameter. On the other hand, the multi-droplet transition velocity decreased and then increased as the orifice diameter increased. At thin orifice thickness, the single droplet diameter approximated the orifice diameter, and increasing the orifice thickness produced a droplet larger than the orifice diameter. In the case of double droplet mode, the diameter of the first droplet showed a similar tendency like the single droplet mode, but the diameter of the second droplet was smaller than that of the first droplet, and the difference between them was affected more by the orifice thickness.

Influence of Initial Diameter on the Combustion Characteristics of n-heptane Droplet (초기 직경이 n-heptane 액적 연소 특성에 미치는 영향)

  • Suh, Hyun Kyu
    • Journal of ILASS-Korea
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    • v.18 no.2
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    • pp.94-99
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    • 2013
  • The spherically-symmetric burning of an isolated droplet is a dynamic problem that involves the coupling of chemical reactions and multi-phase flow with phase change. For the improved understanding of these phenomena, this paper presents the numerical results on the n-heptane droplet combustion conducted at a 1 atm ambient pressure in three different initial droplet diameter ($d_0$). The main purpose of this study is to provide basic information of droplet burning, extinction and flame behavior of n-heptane and improve the ability of theoretical prediction of these phenomena. To achieve these, the numerical analysis was conducted in terms of normalized droplet diameter ($d/d_0$), flame diameter ($d_f$) and flame standoff ratio (FSR) under the assumptions that the droplet combustion can be described by both the quasi-steady behavior for the region between the droplet surface and the flame interface and the transient behavior for the region between the flame interface and ambient surrounding.

Effect of Ultrasonic Frequency on the Atomization Characteristics of Single Water Droplet in an Acoustic Levitation Field (음향 부양장(acoustic levitation field)에서 초음파 주파수(ultrasonic frequency)에 따른 단일 액적의 미립화 특성)

  • Suh, Hyun Kyu
    • Journal of ILASS-Korea
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    • v.18 no.3
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    • pp.126-131
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    • 2013
  • This paper describes the effect of ultrasonic frequency(f) on the atomization and deformation characteristics of single water droplet in an acoustic levitation field. To achieve this, the ultrasonic levitator that can control sound pressure and velocity amplitude by changing frequency was installed, and visualization of single water droplet was conducted with high resolution ICCD and CCD camera. At the same time, atomization and deformation characteristics of single water droplet was studied in terms of normalized droplet diameter($d/d_0$), droplet diameter(d) variation and droplet volume(V) variation under different ultrasonic frequency(f) conditions. It was revealed that increase of ultrasonic frequency reduces the droplet diameter. Therefore, it is able to levitate with low sound pressure level. It also induces the wide oscillation range, large diameter and volume variation of water droplet. In conclusion, the increase of ultrasonic frequency(f) can enhance the atomization performance of single water droplet.

Effect of Intersection Angle of the Flow-focusing Type Droplet Generation Device Channel on Droplet Diameter by using Numerical Simulation Modeling (수치해석 모델링을 이용한 교차 흐름 미세유체 액적 생성 디바이스 채널 교차각이 액적 직경에 미치는 영향)

  • Kim, Shang-Jin;Kang, Hyung-Sub;Yang, Yeong-Seok;Kim, Gi-Beum
    • Journal of Biomedical Engineering Research
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    • v.36 no.3
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    • pp.61-68
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    • 2015
  • In this paper, we studied the effects of intersection angles of the flow-foucusing type droplet generation device inlet channel on droplet diameter using numerical simulation modeling. We modeled different intersection angles with a fixed continuous channel width, dispersed channels width, orifices width, and expansion channels width. Numerical simulations were performed using COMSOL Multiphysics$^{(R)}$ to solve the incompressible Navier-Stokes equations for a two-phase flow in various flow-focusing geometries. Modeling results showed that an increase of the intersection angle causes an increase in the modification of the dispersed flow rate ($v^{\prime}{_d}$), and the increase of the modification of the continuous flow rate ($v^{\prime}{_c}$) obstructs the dispersed phase fluid flow, thereby reducing the droplet diameter. However, the droplet diameter did not decrease, even when the intersection angle increased. The droplet diameter decreased when the intersection angle was less than $90^{\circ}$, increased at an intersection angle of $90^{\circ}$, and decreased when the intersection angle was more than $90^{\circ}$. Furthermore, when the intermediate energy deceased, there was a decrease in the droplet diameter when the intersection angle increased. Therefore, variations in the droplet diameter can be used to change the intersection angle and fluid flow rate.

A Study on the Droplet Size Distribution of Ultra High Pressure Diesel Spray on Electronic Hydraulic Fuel Injection System (전자유압식 분사계에 의한 초고압 디젤분무의 입경분포에 관한 연구)

  • Jang, S.H.;Ahn, S.K.
    • Journal of Power System Engineering
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    • v.2 no.1
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    • pp.25-30
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    • 1998
  • In order to investigate the droplet size distribution and Sauter Mean Diameter in a ultra high pressure diesel spray, fuel was injected with ultra high pressure into the environments of high pressure and room temperature by an Electronic Hydraulic Fuel Injection System. Droplet size was measured with the immersion liquid sampling technique. The immersion liquid was used a mixture of water-methycellulose solution and ethanol. The Sauter Mean Diameter decreased with increasing injection pressure, with a decrease environmental pressure (back pressure) and nozzle diameter. Increasing the injection pressure makes the fuel density distribution of the spray more homogeneous. An empirical correlation was developed among injection pressure, air density, nozzle diameter and the Sauter Mean Diameter of spray droplets.

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Study on the Combustion Characteristics of Methanol Fuel Droplet (Methanol 연료 액적의 연소 특성에 관한 연구)

  • Suh, Hyun Kyu
    • Journal of ILASS-Korea
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    • v.19 no.3
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    • pp.109-114
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    • 2014
  • The main purpose of this study is to provide basic information of droplet burning, extinction process and flame behavior of methanol fuel and improve the ability of theoretical prediction of these phenomena. For the improved understanding of these phenomena, this paper presents the experimental results on the methanol droplet combustion conducted under various initial droplet diameters ($d_0$), ambient pressure ($P_{amb}$), and oxygen concentration ($O_2$) conditions. To achieve this, the experimental study was conducted in terms of burning rate (K) with normalized droplet diameter ($d/d_0$), flame diameter ($d_f$) and flame standoff ratio (FSR) under the assumptions that the droplet combustion can be described by both the quasi-steady behavior for the region between the droplet surface and the flame interface and the transient behavior for the region between the flame interface and ambient surrounding.

An Experimental Study of Breakup of Impinging Droplets on a Hot Surface (표면 충돌 액적의 분열에 관한 실험적 연구)

  • Ko, Y.S.;Chung, S.H.
    • Transactions of the Korean Society of Automotive Engineers
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    • v.2 no.5
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    • pp.85-92
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    • 1994
  • Characteristics of breakup of a liquid droplet impinging on a hot surface has been investigated experimentally by using decane fuel. Factors influencing droplet breakup are surface temperature, impinging velocity, droplet diameter and incident angle. Droplets impinging on a hot surface begins to breakup at $220{\sim}235^{\circ}C$. This temperature varies with impinging Velocity, droplet diameter and incident angle. For wall temperature of $220{\sim}245^{\circ}C$ and above $270^{\circ}C$, breakup probability increases as impinging velocity increases showing S shape curve. For $245{\sim}265^{\circ}C$, a local minimum heat transfer rate occurs. In this temperature range, breakup probability shows nonmonotonous behavior as functions of impinging velocity. As droplet diameter decreases, impinging velocity required for droplet breakup increases. An optimum impinging angle for droplet breakup exists which are found to be about $75^{\circ}$.

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Characteristic of Evaporation Cooling in Water Droplet Impinging on Steel with Various Surface Roughness and Droplet Diameter (강에서 표면조도의 변화와 액적 직경에 따른 충돌 액적 증발 냉각 특성)

  • Jang, C.S.;Sohn, C.H.;Chung, S.W.;Choi, W.S.
    • Journal of the Korean Society for Heat Treatment
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    • v.19 no.3
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    • pp.141-148
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    • 2006
  • An experimental study is presented for water droplet impingement on a steel surface in the process of heat treatment. The objective of the present work is to examine characteristic of evaporation cooling due to surface roughness and droplet diameter under conductive heat input condition. The surface temperatures varied from $80{\sim}155^{\circ}C$, surface roughness was from $R_a=0.12{\mu}m$ to $R_a=1.14{\mu}m$ and droplet diameter was from 2.4 mm to 3.0 mm. The results show that the total evaporation time is shorter for the larger surface roughness and the smaller droplet size, the time average heat flux has maximum value for the larger surface roughness and the smaller droplet size. The total evaporation time has not influence on the nuclear boiling region.

Evaporation Cooling of Water Droplet on Aluminum with Various Surface Roughness and Droplet Diameter in Conductive Condition (전도조건 하에서 표면조도와 액적 직경의 변화에 따른 알루미늄의 액적 증발 냉각)

  • Jang, C.S.;Choi, W.S.
    • Journal of the Korean Society for Heat Treatment
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    • v.18 no.6
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    • pp.375-382
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    • 2005
  • This paper presents the results of experimental investigation for the effect of heat conduction on the evaporation cooling of water droplet in the process of heat treatment. The experiments are mainly focused on the surface temperature, the surface roughness and the droplet diameter at aluminum. The range of surface temperature is from $80^{\circ}C$ to $140^{\circ}C$, surface roughness is from $R_a=0.18{\mu}m$ to $R_a=1.36{\mu}m$ and droplet diameter is from 2.4 mm to 3.0 mm. The results show that the total evaporation time is shorter for the larger surface roughness, the time averaged heat flux has maximum value for the larger surface roughness and exist the critical heat flux. The total evaporation time has a big influence on the evaporation region for the smaller droplet size, but the total evaporation time has not influence on the nuclear boiling region.

Spray Characteristics of Fuel Injector in DI Diesel Engine (직접 분사식 디젤 기관 인젝터의 연료 분무 특성)

  • 이창식;김민규;전원식;진다시앙
    • Transactions of the Korean Society of Automotive Engineers
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    • v.9 no.5
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    • pp.75-81
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    • 2001
  • This paper presents the atomization characteristics of single hole injector in the direct injection type diesel engine. The spray characteristics of fuel injector such as the droplet size and velocity were measured by phase Doppler particle analyzer. In this paper, the atomization characteristics of fuel spray are investigated for the experimental analysis of the measuring data by the results of mean diameter and mean velocity of droplet. The effect of fuel injection pressure on the droplet size shows that the higher injection pressure results in the decrease of mean droplet diameter in the fuel spray. The minimum size of fuel spray droplet appears on the location of 40mm axial distance from nozzle exit of diesel injector. Based on the experimental results, the correlation between the droplet diameter and mean velocity of the diesel spray due to the change of axial and radial distance from the nozzle tip were investigated.

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