• Title/Summary/Keyword: 이중원관

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Thermal-flow Characteristics of Magnetic Fluid for Concentric Annuli Under Fixing Magnetic Field Using Visualization Technique (가시화기법을 이용한 고정자장에서 이중원관내 자성유체의 열유동 특성에 관한 연구)

  • Kim, Hyung-Jin;Seo, Jae-Hyeong;Kim, Dae-Wan;Lee, Moo-Yeon;Seo, Lee-Soo
    • Journal of the Korean Magnetics Society
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    • v.23 no.1
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    • pp.26-30
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    • 2013
  • This article is experimentally to investigate thermal-flow characteristics of the magnetic fluid for concentric annuli under externally fixed magnetic fields using visualization technique. Temperatures of the inner tube and outer tube in the tested concentric annuli were constantly maintained at both $30^{\circ}C$ and $25^{\circ}C$ and the middle tube was filled with the magnetic fluid. Magnetic field was uniformly applied using 4 permanent magnets at 4 directions of the concentric annuli. As a result, the thermal-flow characteristics of the magnetic fluid for concentric annuli could be controlled by directions of the external magnetic fields.

Experimental Study on the Natural Convective Heat Transfer Characteristics of Ferrofluid for Concentric Annuli under Rotating Magnetic Field (회전수 및 자기장강도 변화에 따른 이중원관내 자성유체의 자연대류 열전달 특성에 관한 실험적 연구)

  • Kim, Hyung-Jin;Seo, Jae-Hyeong;Kim, Dae-Wan;Lee, Moo-Yeon;Seo, Lee-Soo
    • Journal of the Korean Magnetics Society
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    • v.23 no.2
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    • pp.77-81
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    • 2013
  • The objective of this study is experimentally to investigate natural convective heat transfer characteristics of the ferrofluid for a concentric annuli under rotating magnetic field with variations of the revolution and the magnetic field strength. The rotating magnetic field was provided by induction motor with 6 poles and 3 phases and the revolution and the magnetic field strength were controlled by an inverter driver and a voltage meter, respectively. Temperatures of the inner pipe and the outer pipe in the tested concentric annuli were maintained at $30^{\circ}C$ and $25^{\circ}C$, respectively, during the test and the direction of the rotating magnetic field was a counterclockwise. As a result, the natural convective heat transfer characteristics of the ferrofluid for a concentric annuli were increased with the rise of the revolution and magnetic field strength due to the increased heat dissipation between hot side and cold side of the concentric annuli.

Characteristics of Heat Transfer of Natural Convection for Magnetic Fluids in Annular Pipes (이중원관내 자성유체의 자연대류에 대한 전열특성)

  • Park, J.W.;Jun, C.H.;Seo, L.S.;Ryu, S.O.
    • Journal of the Korean Magnetics Society
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    • v.12 no.2
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    • pp.73-79
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    • 2002
  • Compared with Newtonial fluids, magnetic fluids have effects on magnetic force. In this study, the purpose is to research the heat transfer characteristic of magnetic fluids which have metalic and fluid characteristics as the external pipe is being cooled and internal pipe is heated. This study found the experimental results from the study of the variety of natural convection for magnetic fluids and the characteristics of the heat transfer by using numerical analysis according to the strength and direction of the magnetic fields from being imposed from the outside. Natural convection of magnetic fluids was controlled by the impressed magnetic fields, and the result of mean nusselt number was calculated. If the impressed magnetic field is in the direction of gravity or the strength of impressed magnetic field is more than -14 mT in the opposite direction, the heat transfer is more than that without the impressed magnetic field. If the strength of impressed magnetic field is less than -14 mT in the opposite direction, it is smaller than that without the impressed magnetic field. Especially, when the strength of the magnetic field is -14 mT, the heat transfer was at the minimum.

Fundamental Study on In-line type Design of Patrol Ship Shipboard Eductors (패트롤 선박용 인라인 이덕터 설계에 관한 기초연구)

  • Kim, Dong-Chan;Cho, Dae-Hwan;Kim, Keun-byeol;Seo, Kwang-Cheol;Lee, Gyoung-Woo
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • 2015.10a
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    • pp.69-70
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    • 2015
  • 이덕터는 구동부를 통해 공급되는 작동유체가 노즐을 통과하면서 고속으로 분출됨으로써 벤츄리 효과에 의해 노즐 출구 주위에 부압이 형성됨에 따라 흡입부를 통해 유체가 흡입된다. 이덕터의 주요 설계인자는 노즐의 직경과 스로트의 직경 및 직관부 길이 그리고 노즐과 직관부 시작점까지의 거리이다. 이 연구에서는 선박용 인라인 이덕터에 대한 기초연구로서 흡입 메카니즘을 체계적으로 해석할 목적으로 주요 설계인자를 이론적으로 고찰하고 설계인자의 변화에 따른 성능실험 가능하도록 이중원관의 형태로 모델링하였다.

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Effect of supercooling on the cooling in horizontal cylindrical annuli (이중원관의 냉각과정에 미치는 과냉각의 영향)

  • Yun, Jeong-In;Kim, Jae-Dol;Kato, Toyofumi
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.10
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    • pp.3313-3321
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    • 1996
  • A fundamental study in cooling and solidification process focused on ice storage was performed, including the interesting phenomena of density inversion, supercooling and dendritic ice. A numerical study was performed for natural convection and ice formation in the cooling and freezing processes with supercooling in a space between double cylinders. When water was cooled under the freezing point by a cooling wall in a cavity, solidification was not started at once, but a subcooled region was formed near the wall. Especially, when the cooling rate was low, subcooled region extended to a wide area. However, after a few minutes, supercooling is released by some triggers. Dendritic ice is suddenly formed within a subcooled region, and a dense ice layer begins to be developed from the cooling wall. Due to the difficulties, most previous studies on solidification process with numerical methods had not treated the supercooling phenomena, i.e. the case considering only the growth of dense ice. In this study, natural convection and ice formation considering existence of supercooling and dendritic ice were analyzed numerically with using finite difference method and boundary fixing method. The results of numerical analysis were well compared with the experimental results.

A Study on the Ultrasonic Effect for Turbulence Enhancement in the Flow Field of a Coaxial Circular Pipe (동심원관 유동장에서 난류증진을 위한 초음파 영향에 관한 연구)

  • Song, Min-Geun;Koo, Ja-Hoon;Lee, Sang-Bum;Son, Seung-Woo;Ju, Eun-Sun
    • Proceedings of the KSME Conference
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    • 2001.06e
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    • pp.742-747
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    • 2001
  • A study on the ultrasonic effect for turbulence enhancement is carried out in the horizontal flow field of a coaxial circular pipe. A large transparent acryl tank is made to perform several experiments for the above research. The front flow field from jet exit is divided as 4 measuring regions to observe characteristics of the above flow field according to those with and without ultrasonic. An ultrasonic transducer with 2MHz high frequency is used to give them the ultrasonic forcing. Characteristics such as the velocity distribution, the kinetic energy and the turbulence intensity are visualized, observed, examined and considered at Re No. 2000. In results, it is clarified that the ultrasonic increases the turbulence enhancement. And the optimum and harmonious intensity suited to the power of flow is needed to maximize the turbulence enhancement.

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Experimental study of natural convection for magnetic fluids in annular pipes (이중원관내 자성유체의 자연대류에 관한 실험적 연구)

  • Park, Joung-Woo;Lee, Jun-Hee;Seo, Lee-Soo
    • Proceedings of the KSME Conference
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    • 2001.06e
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    • pp.191-195
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    • 2001
  • The applications of magnetic fluid can be normally made by 1) using changes of a property of matter caused by applied magnetic field; 2) preserving magnetic fluid at a certain position or in a magnetic fluid keeping the body in a floating condition; 3) controlling the flow of magnetic fluid by means of magnetic field. However, these are usually made by using their methods together. In this study, the natural convection flow of a magnetic fluid in annular pipes is experimentally analyzed. High temperature is kept constantly inside of a circular pipe of experimental model, on the other hand, low temperature is kept constantly outside of it. In experiments, several cases are carried out in order to clarify the fluence of direction and intensity of magnetic fields on the natural convection of magnetic fluid. Therefore magnetic fields are applied in various intensity and up and down directions by permanent magnets.

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A Study on the Flow Characteristics in Double Coaxial Pipe Jets (동축이중원관 분류에 있어서의 유동 특성에 관한 연구)

  • Shin, C.H.;Kim, K.H.
    • Journal of ILASS-Korea
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    • v.1 no.4
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    • pp.46-53
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    • 1996
  • The present study is aiming at improving the performance of main nozzle of an air jet loom with a modified reed and auxiliary nozzles. The double coaxial pipe jets consisting of a central air jet and an annular air jet have been experimentally investigated. The duter jet has a potential core and a constant velocity. The inner jet through an inner long pipe is induced by the subatmospheric pressure near the inner nozzle edge, and the jet velocity of an inner pipe is always lower than that of a outer pipe. The static pressures of the main nozzle over a wide range of the nozzle tank pressure were measured, and the nozzle velocity and Mach numbers were analytically calculated. Experiment81 results indicate that the critical condition of Mach number of unity to occur at the two positions in a main nozzle; one of them is the needle tip and the other is the acceleration tube exit An increase in the tank pressure causes the critical throat condition to occur at the two positions above. The velocity of acceleration-tube exit is maximum at the critical length L* and flow patter in acceleration-tube over critical lengh remains unstable.

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Experimental Study of Natural Convection for Magnetic Fluids in Annular Pipes Under the Influence of External Magnetic Fields (이중원관내 자성유체의 외부자장에 대한 자연대류의 실험적 연구)

  • 서이수;박정우;이준희
    • Journal of the Korean Magnetics Society
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    • v.11 no.6
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    • pp.245-249
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    • 2001
  • Natural convection of a magnetic fluid is different from that of Newtonian fluids because magnetic body force exists in an addition to gravity and buoyancy. In this paper, natural convection of a magnetic fluids (W-40) in annular pipes was studied by experimentally. Inside wall was kept at a constant temperature (25 $^{\circ}C$), and outside wall was also held at a constant but lower temperature (20 $^{\circ}C$). The magnetic fields of various magnitude were applied up. This study has resulted in the following fact that the natural convection of a magnetic fluids was controlled by the direction and intensity of the magnetic fields.

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Turbulent Fluid Flow and Heat Transfer in Concentric Annuli with Square-Ribbed Surface Roughness (사각돌출형 표면거칠기가 있는 이중동심원관 내의 난류유동과 열전달)

  • 안수환;이윤표;김경천
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.5
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    • pp.1294-1303
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    • 1993
  • The fully developed turbulent momentum and heat transfer induced by the square-ribed roughness elements on the inner wall surface in concentric annuli is studied analytically based on a modified turbulence model. The analytical results of the fluid flow is verified by experiment. The resulting momentum and heat transfer are discussed in terms of various parameters, such as the radius ratio, the relative roughness, the roughness density, fluid Reynolds number and for heat transfer, fluid Prandtl number. The study demonstrates that certain artificial roughness elements may be used to enhance heat transfer rates with advantages from the overall efficiency point of view.