• Title/Summary/Keyword: 타원형 액적

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Spreading Dynamics of an Ellipsoidal Drop Impacting on a Heated Substrate (고온으로 가열된 고체 표면과 충돌하는 타원형 액적의 퍼짐 거동)

  • Yun, Sungchan
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.41 no.3
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    • pp.205-209
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    • 2017
  • Unlike spherical drop impact, ellipsoidal drop impact can control the bouncing height on a heated surface by significantly altering impact behavior. To scrutinize the effect of the aspect ratio (AR) of the drop on the bounce suppression, in this study, non-axisymmetric spreading behaviors are observed from two side views and characterized based on the spreading width of the drop for horizontal principal axes. In addition, the maximum spreading width is investigated for various ARs. The results show that as the AR increases, the maximum spreading width of the minor axis increases, whereas that of the major axis shows no significant variation. In the regime of high AR and high impact velocity, liquid fragmentations by three parts are observed during bouncing. These fragmentations are discussed in this work. The hydrodynamic features of ellipsoidal drop impact will help understand bouncing control on non-wetting surfaces for several applications, such as self-cleaning and spray cooling.

Shape Detection of Ellipsoidal Droplets Using Randomized Hough Transform (Randomized Hough 변환을 이용한 타원형 액적의 형상 검출)

  • Choo, Yeon-Jun;Kang, Bo-Seon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.10
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    • pp.1508-1515
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    • 2003
  • In this study, the image processing program for deducing parameters of the elliptic shape of the partially overlapped liquid droplets was developed using the randomized Hough transform and the parameter decomposition. The procedure for the shape detection consists of three steps. For the first step, the candidate centers of ellipses are determined by the geometric property of the ellipse. Next, the rest parameters are estimated by the randomized Hough transform. In the final step for the post-processing, optimally approximated parameters of ellipses are determined. The developed program was applied to the simulated overlapped ellipses, real overlapped droplets, and real spray droplets. The shape detection was very excellent unless there existed inherent problems in original images. Moreover, this method can be used as an effective separating method for the overlapped small particles.

Shape Detection of Ellipsoidal Droplets Using Randomized Hough Transform (Randomized Hough 변환을 이용한 타원형 액적의 형상 검출)

  • Choo, Yeon-Jun;Kang, Bo-Seon
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.1783-1788
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    • 2003
  • In this study, the image processing program for deducing parameters of the elliptic shape of the partially overlapped liquid droplets was developed using the randomized Hough transform and the parameter decomposition. The procedure for the shape detection consists of three steps. For the first step, the candidate centers of ellipses are determined by the geometric property of the ellipse. Next, the rest parameters are estimated by the randomized Hough transform. In the final step for the post-processing, optimally approximated parameters of ellipses are determined. The developed program was applied to the simulated overlapped ellipses, real overlapped droplets, and real spray droplets. The shape detection was very excellent unless there existed inherent problems in original images. Moreover, this method can be used as an effective separating method for the overlapped small particles.

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NUMERICAL ANALYSIS OF THE IMPACTING AND SPREADING DYNAMICS OF THE ELLIPSOIDAL DROP ON THE PERFECT NON-WETTING SOLID SURFACE (완전 비습윤 고체 표면 위 타원형 액적의 충돌 및 퍼짐 거동에 대한 수치적 연구)

  • Yun, S.
    • Journal of computational fluids engineering
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    • v.21 no.4
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    • pp.90-95
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    • 2016
  • Leidenfrost drops with ellipsoidal shaping can control the bouncing height by adjusting the aspect ratio(AR) of the shape at the moment of impact. In this work, we focus on the effect of the AR and the impact Weber number(We) on the non-axisymmetrical spreading dynamics of the drop, which plays an important role in the control of bouncing. To understand the impact dynamics, the numerical simulation is conducted for the ellipsoidal drop impact upon the perfect non-wetting solid surface by using volume of fluid method, which shows the characteristics of the spreading behavior in each principal axis. As the AR increases, the drop has a high degree of the alignment into one principal axis, which leads to the consequent suppression of bouncing height with shape oscillation. As the We increases, the maximum spreading diameters in the principal axes both increase whereas the contact time on the solid surface rarely depends on the impact velocity at the same AR. The comprehensive understanding of the ellipsoidal drop impact upon non-wetting surface will provide the way to control of drop deposition in applications, such as surface cleaning and spray cooling.

Internal Flow and Evaporation Characteristic inside a Water Droplet on a Vertical Vibrating Hydrophobic Surface (수직 진동하는 소수성 표면 위 액적의 내부유동 및 증발특성 연구)

  • Kim, Hun;Lim, Hee-Chang
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.39 no.7
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    • pp.579-589
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    • 2015
  • This study aims to understand the internal flow and the evaporation characteristics of a deionized water droplet subjected to vertical forced vibrations. To predict and evaluate its resonance frequency, the theories of Lamb, Strani, and Sabetta have been applied. To visualize the precise mode, shape, and internal flow inside a droplet, the experiment utilizes a combination of a high-speed camera, macro lens, and continuous laser. As a result, a water droplet on a hydrophobic surface has its typical shape at each mode, and complicated vortices are observed inside the droplet. In particular, large symmetrical flow streams are generated along the vertical axis at each mode, with a large circulating movement from the bottom to the top and then to the triple contact line along the droplet surface. In addition, a bifurcation-shaped flow pattern is formed at modes 2 and 4, whereas a large ellipsoid-shape flow pattern forms at modes 6 and 8. Mode 4 has the fastest internal flow speed and evaporation rate, followed by modes 8 then 6, with 2 having the slowest of these properties. Each mode has the fastest evaporation rate amongst its neighboring frequencies. Finally, the droplet evaporation under vertical vibration would lead to more rapid evaporation, particularly for mode 4.

Correlations of Internal Nozzle Flow in Circular and Elliptical Nozzles with External Flow (원형 및 타원형 노즐 내부유동과 외부유동의 상관관계)

  • Ku, Kun-Woo;Hong, Jung-Goo;Park, Cheol-Won;Lee, Choong-Won
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.36 no.3
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    • pp.325-333
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    • 2012
  • An experimental study was carried out to determine the correlation between the internal flow in a circular nozzle and elliptical nozzles with the external flow. The flow rate, spray angle and drop size were measured under various conditions of the injection pressure. Numerical simulations were attempted to investigate the internal flow structure in the elliptical nozzles, because the experimental study was limited in its measurements of flow velocity and pressure distributions in the relatively small orifice. In the case of the elliptical nozzles, the disintegration characteristics of the liquid jet were significantly different from those of the circular nozzle. Surface breakup was observed at the jet issued from the elliptical nozzles with injection pressure. This is due to the internal flow structure, which is reattached to the orifice wall at the minor axis plane of the elliptical nozzle, unlike that observed with the circular nozzle.

The Effect of the Y-jet Nozzle Exit Orifice Shape on Asymmetric Spray (Y-jet 노즐의 출구오리피스 형상이 비대칭 분무에 미치는 영향)

  • Baik, Gwang Yeol;Hong, Jung Goo
    • Journal of ILASS-Korea
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    • v.26 no.1
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    • pp.33-39
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    • 2021
  • Y-jet nozzle has a wide fuel flow rate range and turn-down ratio, thus, it is used in industrial boilers, furnace and agricultural atomizer. However, it has asymmetrical spray characteristics due to the nozzle design factors. Therefore, in this study, asymmetric spraying characteristics of the elliptical Y-jet nozzle was studied by using the lab-scale spray apparatus. As a result, the elliptical Y-jet nozzle had lower gas mass flow rate than circular Y-jet nozzle at same gas pressure, because of bigger shear stress due to the wider inner surface at the elliptical Y-jet nozzle. Larger SMD was measured on the elliptical Y-jet nozzle than the circular Y-jet nozzle. When SMD was measured in the X_Axis direction at the same gas mass flow rate, the elliptical Y-jet nozzle with an aspect ratio of 2:1 showed greater asymmetry than the others.

An Experimental Study of Discharge Coefficient with Non-Circular Effervescent Type Twin-fluid Nozzle (비원형 Effervescent Type 이유체노즐의 Discharge Coefficient에 관한 실험적 연구)

  • Lee, Sang Ji;Park, Hyung Sun;Hong, Jung Goo
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2017.05a
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    • pp.682-685
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    • 2017
  • An experimental study was carried out to investigate the injection characteristics of non-circular effervescent type twin-fluid nozzles. For this purpose, two types of non-circular nozzles (E1, E2) and one kind of circular nozzle (C) were used. At this time, the Aerorator mounted on the nozzle used three different diameters to match the aspect ratio with the nozzle exit area. Therefore, experiments were performed according to three aspect ratios for each nozzle, and a total experiments were conducted. Experiments were carried out by controlling the amount of air flowing after fixing the flow rate of the liquid, and the nozzle internal pressure and SMD were measured, and the jet image was taken from the nozzle. The discharge coefficients of the three kinds of nozzles were compared with the conventional equation and the Jedelsky's equation, and the Jedelsky's equation was found to be about 4 times larger. The droplet size (SMD) injected from the nozzle was found to be smaller in the non-circular shape than in the circular shape, which is expected to be caused by the difference of the discharge coefficient values.

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Atomization Characteristics of Effervescent Twin-fluid Nozzle with Different Nozzle Shapes (노즐 형상에 따른 Effervescent 이유체 노즐의 분무특성)

  • Lee, Sang Ji;Hong, Jung Goo
    • Journal of ILASS-Korea
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    • v.22 no.3
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    • pp.146-152
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    • 2017
  • An experimental study was carried out to investigate the spray characteristics of non-circular effervescent twin-fluid nozzles. For this purpose, two types of non-circular nozzles (E1, E2) and circular nozzle (C) were used. Three types of aerorators with hole diameters of 1.2, 1.7 and 2.1 mm were used. Each aerorator has a total of 12 holes. It is defined by area ratio which is ratio of exit orifice area and aerator hole area. Experiments were carried out by controlling the amount of air flowing after fixing the flow rate of the liquid, and the nozzle internal pressure and SMD were measured, and the jet image was taken from the nozzles. The discharge coefficients of the three kinds of nozzles were compared with the used in plain orifice's equation and the Jedelsky's equation, and the Jedelsky's equation was found to be about 3 times larger. In addition, empirical formula based on ALR, which is the largest variable in Jedelsky's equation, was derived. The droplet sizes(SMD) were found to be smaller in the non-circular shape than in the circular shape, which is concluded to be caused by the difference of the discharge coefficients.