• Title/Summary/Keyword: Nozzle L/D

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A Numerical Study on the Characteristics of Cavitation and Internal Flow According to Nozzle Length-to-Diameter Ratio (노즐 형상비에 따른 캐비테이션 및 내부 유동 특성에 관한 수치적 연구)

  • Han, Dong-Sik;Kim, Hyun-Kyu;Chang, Young-June;Jeon, Chung-Hwan
    • Journal of ILASS-Korea
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    • v.13 no.4
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    • pp.200-205
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    • 2008
  • Spray formation mechanism was controlled by a cavitation inside an injection nozzle. Nozzle geometry affects spray characteristics and formation behavior, which could determine engine performance and pollutant formation. A study was carried out on the influence of aspect ratio on cavitation inside a nozzle. The cavitation model available in Star-CD code was used to obtain cavitation behavior inside nozzle, which was compared with previous experimental results. In this paper, a CFD approach combining multiphase Volume-of-Fluid(VOF) and k-model was applied. The numerical results are similar with the experimental results.

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A study on Behavior of Turbulent Transient Jets with Butane and Propane (Butane 및 propane의 비정상 난류 제트 특성에 관한 연구)

  • Lee, Beom-Ho;Song, Hak-Hyun;Cho, Seung-Hwan;Hong, Sung-Tae;Lee, Dae-Yup;Lee, Tae-Woo
    • Journal of ILASS-Korea
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    • v.15 no.2
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    • pp.74-82
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    • 2010
  • In order to understand the behavior of transient gaseous injection used in an LPG (Liquefied Petroleum Gas) engine, turbulent incompressible transient jets with butane and propane were measured and analyzed at pressures of 1.5 bar and 2.0 bar with injector diameters of 3 mm and 5 mm. Mie-scattering method with a tracer was used, and images were processed to investigate the behavior of butane and propane jets. Distances from the nozzle to transition region were measured as $L_e/d_{inj}$=4.35~19.4, where $L_e$ and $d_{inj}$ indicate respectively a distance from nozzle to transition point and nozzle diameter. Slits and tubes around jet at near-field were introduced to measure the effect of entrainment and the diameter of jet, which revealed that the entrainment of surrounding air is significant for developing jet diameter. When the entrainment is restricted, the behavior of jet became deviating from the baseline. It was found that the virtual origin located outside of a nozzle towards jet tip within the conditions of this work, and its location was estimated as $x_o/d_{inj}$=0.56~7.25, where $x_o$ is a distance from nozzle to virtual origin.

Heat transfer and flow characteristics of a circular jet impinging on a convex curved surface (볼록한 반구면에 충돌하는 원형제트의 열전달 및 유동특성)

  • Lee, Dae-Hui;Jeong, Yeong-Seok;Im, Gyeong-Bin;Kim, Dae-Seong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.4
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    • pp.579-588
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    • 1997
  • The heat transfer and flow measurements from a convex curved surface to a circular impinging jet have been made. The flow at the nozzle exit has a fully developed velocity profile. The jet Reynolds number (Re) ranges from 11,000 to 50,000, the dimensionless nozzle-to-surface distance (L/d) from 2 to 10, and the dimensionless surface curvature (d/D) from 0.034 to 0.089. The results show that the stagnation point Nusselt number (N $u_{st}$ ) increases with increasing value of d/D. The maximum Nusselt number at the stagnation point occurs at L/d .ident. 6 to 8 for all Re's and d/D's tested. For larger L/d, N $u_{st}$ dependency on Re is stronger due to an increase of turbulence in the approaching jet as a result of the more active exchange of momentum with a surrounding air. The local Nusselt number decreases monotonically from its maximum value at the stagnation point. However, for L/d=2 and Re=23,000, and for L/d.leq.4 and Re=50,000, the stream wise Nusselt number distributions exhibit secondary maxima at r/d .ident. 2.2. The formation of the secondary maxima is attributed to an increase in the turbulence level resulting from the transition from a laminar to a turbulent boundary layer.ndary layer.

Intermittent Atomization Characteristics of Multi-Hole and Single-Hole Diesel Nozzle

  • Lee, Jeekuen;Kang, Shin-Jae;Park, Byungjoon
    • Journal of Mechanical Science and Technology
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    • v.16 no.12
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    • pp.1693-1701
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    • 2002
  • The intermittent spray characteristics of a multi-hole and a single-hole diesel nozzle were experimentally investigated. The hole number of the multi-hole nozzle was 5, and the hole diameter of the 5-hole and the single-hole nozzle was the same as d$\_$n/=0.32 ㎜ with the constant hole length to diameter ratio(l$\_$n//d$\_$n/=2.81). The droplet diameters of the spray, including the time-resolved droplet diameter, SMD (Sauter mean diameter) and AMD (arithmetic mean diameter) , injected intermittently from the two nozzles into the still ambient were measured by using a 2-D PDPA (phase Doppler particle analyzer). Through the time-resolved evolutions of the droplet diameter, it was found that the structure of the multi-hole and the single-hole nozzle spray consisted of the three main parts : (a) the leading edge affected by surrounding air. and composed of small droplets; (b) the central part surrounded by the leading edge and mixing flow region and scarcely affected by the resistance of air, (c) the trailing edge formed by the passage of the central part. The SMD decreases gradually with the increase in the radial distance, and the constant value is obtained at the outer region of the radial distance (normalized by hole diameter) of 7-8 and 6 for the 5-hole and single-hole nozzle, respectively. The SMD along the centerline of the spray decrease shapely with the increase in the axial distance after showing the maximum value near the nozzle tip. The SMD remains the constant value near the axial distance(normalized by hole diameter) of 150 and 180 for the 5-hole and the single-hole nozzle, respectively.

Characteristics of Internal Flow and Fuel Spray in a Fuel Nozzle Orifice (연료노즐의 내부유동 및 외부분무 특성)

  • Hong, S.T.;Park, J.H.;Koo, J.Y.
    • Journal of ILASS-Korea
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    • v.1 no.1
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    • pp.76-84
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    • 1996
  • The nozzle geometry and up-stream inject ion condition affect the characteristics of flow inside the nozzle. such as turbulence and cavitation bubbles. Flow details in fuel nozzle orifice with sudden contraction of cross sectional area have been investigated both experimentally and numerically. The measurements of velocities of internal flow in a scaled-up nozzle with different length to diameter rat io(L/d) were made by laser Doppler velocimetry in order to clarify the effect of internal flow on the characteristics of fuel spray. Mean and fluctuating velocities and discharge coefficients were obtained at various Reynolds numbers. The turbulent intensity and turbulence kinetic energy in a sharp inlet nozzle were higher than that in a round inlet nozzle. Calculations were also performed for the same nozzles as scaled-up experimental nozzles using the SIMPLE algorithm. External spray behavior under different nozzle geometry and up-stream flow conditions using Doppler technique and visualization technique were also observed.

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The Study on the Phenomenon of Heat Transfer on a Downward Isothermal Circular Surface by an Impinging of Upward Circular Nozzle Jet (상향 원형노즐 제트에 의한 하향 등온 원형평면에서의 열전달 현상에 관한 연구)

  • Lee, In Jae;Eom, Yong Kyoon
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.28 no.11
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    • pp.450-457
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    • 2016
  • While many studies on the heat transfer effect of an impinging jet have been published, most studies focus on the downward impinging jet. This study investigates the impinging jet heat transfer phenomenon when water at a temperature of $24^{\circ}C$ impinges on the downward isothermal circular plate at 60, 70, and $80^{\circ}C$ and when the upward round jet nozzle is 4, 6, and 8 mm diameter with a flow rate 3.6, 4.6, and 5.6 L/min, respectively, and when the ratio of the nozzle clearance/nozzle diameter (H/D) is 1. The results showed that, as the nozzle diameter decreases, the heat transfer coefficient increases at a constant flow rate. The correlation equation of $Nu_r$, $Pr_r$, and $Re_{jg}$ is obtained in the impinging and constant velocity flow region $(Nu_r/Pr^{0.4}_r)Dr=4.6[Re_{jg}(r/R_c)Dr]^{0.8}$ at all flow rates, in the deceleration and falling flow regions $(Nu_r/Pr^{0.4}_r)Dr=42.7{\mid}Re_{jg}(r/R_c)Dr-345.7{\mid}^{0.3}$ at 3.6 L/min, $(Nu_r/Pr^{0.4}_r)Dr=92.4{\mid}Re_{jg}(r/R_c)Dr-16.8{\mid}^{0.2}$ at 4.6 L/min, and $(Nu_r/Pr^{0.4}_r)Dr=322.4{\mid}Re_{jg}(r/R_c)Dr-536.2{\mid}^{0.01}$ at 5.6 L/min.

A Study on the Heat Transfer Characteristics of Turbulent Round Jet Impinge on the Inclined Concave Surface Using Transient Liquid Crystal Method (과도액정 기법을 이용한 오목표면 경사각도에 따른 난류 충돌 제트의 열전달 특성에 관한 연구)

  • Lim Kyoung-Bin;Lee Chang-Hee;Lee Sang-Hoon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.30 no.7 s.250
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    • pp.656-662
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    • 2006
  • The effects of concave hemispherical surface with inclined angle on the local heat transfer from a turbulent round jet impinging were experimentally investigated using transient liquid crystal method. This method suddenly exposes a preheated wall to an impinging jet and then the video system records the response of liquid crystals for the measurement of the surface temperature. The Reynolds numbers were used 11000, 23000 and 50000, nozzle-to-surface distance ratio from 2 to 10 and the surface angles $\alpha=0^{\circ},\;15^{\circ},\;30^{\circ}\;and\;40^{\circ}$. Correlations of the stagnation point Nusselt number according to Reynolds number, jet-to-surface distance ratio and dimensionless surface angle are investigated. In the stagnation point, in term of $Re^n$, n ranges from 0.43 in case of $2{\leq}L/d\leq6$ to 0.45 in case of $6. The maximum Nusselt number occurs in the direction of upstream. The displacement of the maximum Nusselt number from the stagnation point increases with increasing surface angle or decreasing nozzle-to-surface distance. The maximum displacement is about 0.7 times of the jet nozzle diameter.

INTERNAL FLOW PROPERTIES AND THRUST CHARACTERISTICS OF AXI-SYMMETRIC ANNULAR BELL TYPE EJECTOR-JET (축대칭 환형 이젝터 제트의 내부 유동과 추력특성)

  • Park, G.H.;Kwon, S.J.
    • Journal of computational fluids engineering
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    • v.12 no.2
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    • pp.46-52
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    • 2007
  • An experimental and numerical investigation of the ejector-jets focusing on its geometric parameters that effect on thrust performance was carried out. The area ratio of the primary nozzle that was tested in the present study was 2.17 and 3.18, while the ratio of the length to the diameter of the duct downstream the primary nozzle inlet had values of 3.41, 6.82, and 10.23. Internal flow properties of ejector-jet were estimated by comparison experiment data and CFD analysis for basic study of ejector-jet thrust performance. For examination of thrust performance, the thrust ratios increased with increase in L/D. Especially at AR=2.17, the maximum thrust augmentation was 33 percent for the shortest L/D. It is expected that the increase of mixing duct length of ejector-jet will be helpful in a thrust performance by improving mixing efficiency.

INTERNAL FLOW PROPERTIES AND THRUST CHARACTERISTICS OF AXI-SYMMETRIC ANNULAR BELL TYPE EJECTOR-JET (축대칭 환형 이젝터 제트의 내부 유동과 추력특성)

  • Park, G.H.;Kwon, S.J.
    • 한국전산유체공학회:학술대회논문집
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    • 2007.04a
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    • pp.166-170
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    • 2007
  • An experimental and numerical investigation of the ejector-jets focusing on its geometric parameters that effect on thrust performance was carried out. The area ratio of the primary nozzle that was tested in the present studywas 2.17 and 3.18, while the ratio of the length to the diameter of the duct downstream the primary nozzle inlet had values of 3.41, 6.82, and 10.23. Internal flow properties of ejector-jet were estimated by comparison experiment data and CFD analysis for basic study of ejector-jet thrust performance. For examination of thrust performance, the thrust ratios increased with increase in L/D. Especially at AR=2.17, the maximum thrust augmentation was 34 percent for the shortest L/D. It is expected that the increase of mixing duct length of ejector-jet will be helpful in a thrust performance by improving mixing efficiency.

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Performance Improvement of Polymer Deposition System by Nozzle Guide and Its Application to Washer Scaffold Fabrication (노즐 가이드를 적용한 폴리머 적층 시스템의 Washer Scaffold 제작을 위한 성능 개선)

  • Sa, Min-Woo;Kim, Jong Young
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.37 no.3
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    • pp.249-257
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    • 2013
  • Rapid prototyping was used to design and develop a three-dimensional (3D) scaffold for tissue engineering application. In this study, the nozzle guide (TB-CP-HN, MUSASHI ENGINEERING, INC., JAPAN) used with the syringe of the polymer deposition system (PDS) was evaluated by measuring the scaffold line width and height. 3D scaffolds were fabricated using a biodegradable polymer called poly-caprolactone (PCL). The PCL polymer can be deposited from the needle of a syringe using a 200-${\mu}m$ precision nozzle, at a pressure of 600 kPa and temperature of $125^{\circ}C$. The advantages and improvements in this nozzle guide were addressed through washer scaffold fabrication. Overall, this research indicated that the fabrication of a complex-shaped scaffold using an enhanced polymer deposition system may have potential for tissue engineering.