• Title/Summary/Keyword: 금박막 필름

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The Effect of Nozzle Diameter on Heat Transfer to a Fully Developed Round Impinging Jet (완전 발달된 원형 충돌제트의 노즐 직경이 열전달에 미치는 영향)

  • Lee, Dae-Hee;Won, Se-Youl;Lee, Young-Min;Cho, Heon-No
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.4
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    • pp.519-525
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    • 2000
  • The effect of nozzle diameter on the local Nusselt number distributions has been investigated for an axisymmetric turbulent jet impinging on the flat plate surface. The flow at the nozzle exit has a fully developed velocity profile. A uniform heat flux boundary condition at the plate surface was created using gold film Intrex. Liquid Crystal was used to measure the plate surface temperature. The experiments were made for the jet Reynolds number (Re) 23,000, the dimensionless nozzle to surface distance (L/d) from 2 to 14, and the nozzle diameter (d) from 1.36 to 3.40 cm. The results show that the Nusselt number at and near the stagnation point increase with an increasing value of the nozzle diameter.

A Comparative Study on the Convective Heat Transfer Measurement Technique based on Liquid Crystal (액정을 이용한 대류 열전달 측정 방법의 비교 연구)

  • 정기호;송기범;고기탁;김귀순
    • Journal of the Korean Society of Propulsion Engineers
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    • v.6 no.3
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    • pp.37-43
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    • 2002
  • There have been numerous experimental studies for heat transfer measurement technique. This study investigates optical methods for measuring local heat transfer coefficient using thermochromic liquid crystal. Transient and steady methods have been utilized to measure local heat transfer coefficient on a cylinder with a cross flow. The steady method is based on the heat-coating technique and two transient methods adopt by-pass technique and insertion technique, respectively. Both techniques of transient method employ heating technique in which the flow is heated by using the electric heater and cooling technique which cools the preheated cylinder. Experimental results indicate that each methods have nearly similar results. Detailed discussions have been made for its own advantages and disadvantages.

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.

Heat Transfer Enhancement by the Perforated Plate of Round Impinging Air Jets (원형충돌제트에서 다공질판에 의한 열전달 향상)

  • Kim, Yun-Taek;Lee, Yeong-Min;Won, Se-Yeol;Lee, Dae-Hui
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.4
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    • pp.475-484
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    • 2001
  • The purpose of this study is to investigate the heat transfer augmentation using the perforated plate placed in front of a target plate in an axisymmetric impinging air jet system. The new liquid crystal technique using neural networks with median filtering is used to determine the Nusselt number distributions on the target surface. The experiments were made for the jet Reynolds number (Re) 23,000. The effects of the pitch-to-diameter (p/d1) from 1.5 to 2.5 in the perforated plate, the hole diameter on perforated plate (d1) from 4㎜ to 12㎜, the perforated plate to target surface distance (z/d1) from 1 to 3, and the nozzle-to-target surface distance (L/d) from 2 to 10 on the heat transfer characteristics were experimentally investigated. It was found that when the perforated plate was located between the nozzle exit and the target plate, the average heat transfer rate at the stagnation region corresponding to r/d$\leq$1.0 was increased up to the maximum 2.3 times compared to the case without the perforated plate.