• 제목/요약/키워드: 공진대류

검색결과 8건 처리시간 0.022초

사각 공동구의 벽면 가진에 의한 자연 대류 유동의 공진 현상 및 열전달에 관한 연구 (Resonance of Natural Convection and Heat Transfer inside a Square Cavity due to a Vibrating Wall)

  • 허남건;김영규;강병하
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2001년도 춘계학술대회논문집D
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    • pp.483-488
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    • 2001
  • In the present study a numerical simulation is performed on a natural convection inside a square cavity with a vibrating wall. The study has been conducted varying the heat transfer rate, wall excitation frequency and also the orientation of the cavity. The temperature and velocities inside the cavity was observed and also, the heat transfer coefficients on the heating wall was seen. From the results, it can be seen that the temperature inside the cavity decreases when excited with the proper frequency and the heat transfer coefficient increased with cavity inclination angle, ${\theta}$. It is also found from the results that flow resonance is occurred near the inclination angle ${\theta}=90^{\circ}$.

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종횡비가 변하는 공동 내 자연대류의 공진주파수 (Resonance Frequency of the Natural Convection in the Closure Cavity for the Variable Aspect Ratio)

  • 전건호;주광섭;최영돈
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2000년도 추계학술대회논문집B
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    • pp.609-614
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    • 2000
  • This numerical study investigate resonance frequency of natural convection for steady state, periodic flow and chaotic flow in two-dimensional direct numerical simulations, differentially heated, vertical cavities having aspect ratios near unity. The enclosure cavity has isothermal and time dependent temperature side walls and adiabatic top/bottom walls. The aspect ratio is 1/3, 1/2, 1, 2, and 3 for the varying Rayleigh number. Resonance frequency for AR=1 has decrease as the aspect ratio and the Rayleigh number are increasing.

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간헐 열전달을 이용한 밀폐용기내의 물질전달 향상 (Enhancement of Mass Transfer of an Enclosed Fluid by Time-periodic Thermal Forcing)

  • 곽호상
    • 한국전산유체공학회지
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    • 제7권1호
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    • pp.36-43
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    • 2002
  • A numerical investigation is made of unsteady double-diffusive convection of a Boussinesq fluid in a rectangular cavity subject to time-periodic thermal excitations. The fluid is initially stratified between the top endwall of low solute concentration and the bottom endwall of high solute concentration. A time-dependent heat flux varying in a square wave fashion, is applied on one sidewall to induce buoyant convection. The influences of the imposed periodicity on double-diffusive convection are examined. A special concern is on the occurrence of resonance that the fluctuations of flow and attendant heat and mass transfers are mostly amplified at certain eigenmodes of the fluid system. Numerical solutions illustrate that resonant convection results in a conspicuous enhancement of time-mean mass transfer rate.

저 주파수 벽면 가진에 의한 밀폐공간 내부 온도장의 공진 특성 실험 (An Experimental Study on Resonance of Temperature Field by Low-Frequency Oscillating Wall in a Side Heated Enclosure)

  • 김서영;김성기;최영돈
    • 대한기계학회논문집B
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    • 제25권9호
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    • pp.1272-1280
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    • 2001
  • An experimental study has been conducted to elucidate the resonance of natural convection in a side-heated square enclosure having a mechanically oscillating bottom wall. Under consideration is the impact of the imposed oscillating frequency, amplitude and the system Rayleigh number on the fluctuation of air temperatures. The experimental results show that the magnitude of the fluctuation of air temperature is substantially augmented at a specific forcing frequency of the oscillating bottom wall. The resonant frequency is increased with the increase of the Rayleigh number and it is little affected by the amplitude of the oscillating wall. It is also found that the resonant frequency is relevant to the Brunt- V$\"{a}$iS$\"{a}$l$\"{a}$ frequency which represents the stratification degree of the system.

사각 공동구의 하부 벽면 가진의 진폭 변화에 따른 자연 대류 유동의 공진 현상에 관한 연구 (Amplitude Effect on the Resonance of Natural Convection inside a Square Cavity with a Vibrating Bottom Wall)

  • 허남건;김욱;김영규;강병하
    • 한국전산유체공학회:학술대회논문집
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    • 한국전산유체공학회 2000년도 추계 학술대회논문집
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    • pp.66-71
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    • 2000
  • In the present study a numerical simulation is performed on a natural convection inside a square cavity with a vibrating bottom wall. The heat transfer coeffcients for various amplitudes of the bottom wall vibration were compared to the case without the bottom wall excitation. From the results, it is seen that the local temperature distribution in a cavity becomes more uniform as the amplitude of the bottom wall vibration is increased. Also, it was seen that the heat transfer coefficient increased on the heating wall as the applied amplitude increased.

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초음파진동에 의한 음향유동을 활용한 냉각 메카니즘의 실험 및 이론적 연구 (Experimental and Analytical Study of a Cooling Mechanism Using Acoustic Streaming by Ultrasonic Vibrations)

  • Loh, Byoung-Gook;Lee, Dong-Ryul
    • 한국소음진동공학회논문집
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    • 제13권9호
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    • pp.694-702
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    • 2003
  • 초음파 진동에 의한 음향유동을 활용한 냉각 메카니즘과 대류열전달 향상에 관한 연구가 실험 및 이론적으로 수행되었다. 음향유동 형태와 열전달 특성이 제시되었다. Nyborg 이로에 의한 가열판의 이론적 과도 온도분포는 실험에 의해 측정되었다. 10$\mu\textrm{m}$의 진폭으로 4분안에 3$0^{\circ}C$의 온도강하가 발생하였다. 진폭을 25$\mu\textrm{m}$로 증가시킴에 따라 본 연구의 실험장비에서 습득할 수 있는 최대 온도강하인 4$0^{\circ}C$를 얻을 수 있었다. 실험에서 측정할 수 있었던 주파수 28.4kHz에서의 진폭 25$\mu\textrm{m}$ 조건에서의4$0^{\circ}C$의 온도강하를 이론적 열전달 해석으로도 검증할 수 있었다.

초음파 진동에 의해 발생된 음향유동을 활용한 급속냉각 메카니즘 (Rapid Cooling Mechanism Utilizing Acoustic Streaming Generated by Ultrasonic Vibrations)

  • 노병국;권기정;이동렬
    • 한국소음진동공학회논문집
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    • 제16권10호
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    • pp.1057-1066
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    • 2006
  • Acoustic streaming Induced by longitudinal vibration at 30 kHz is visualized for a test fluid flow between the stationary glass plate and ultrasonic vibrating surface with particle imaging velocimetry (PIV) To measure an increase in the velocity of air flow due to acoustic streaming, the velocity of air flow in a gap between the heat source and ultrasonic vibrator is obtained quantitatively using PIV. The ultrasonic wave propagating into air in the gap generates steady-state secondary vortex called acoustic streaming which enhances convective cooling of the stationary heat source. Heat transfer through air in the gap is represented by experimental convective heat transfer coefficient with respect to the gap. Theoretical analysis shows that gaps for maximum heat transfer enhancement are the multiple of half wavelength. Optimal gaps for the actual design are experimentally found to be half wavelength and one wavelength. A drastic temperature variation exists for the local axial direction of the vibrator according to the measurement of the temperature distribution in the gap. The acoustic streaming velocity of the test fluid in the gap is at maximum when the gap agrees with the multiples of half wavelength of the ultrasonic wave, which are specifically 6 mm and 12 mm.

초음파 진동자에 의해 유도된 음향유동을 이용한 첨단 냉각법 (A Novel Cooling Method by Acoustic Streaming Induced by Ultrasonic Resonator)

  • 노병국;이동렬
    • 한국음향학회지
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    • 제22권3호
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    • pp.217-223
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    • 2003
  • 30 ㎑의 초음파 (ultrasonic wave)의 미세 진동에 의해서 유도된 음향유동 (acoustic streaming)에 의한 공기대류를 이용한 새로운 냉각방법을 소개한다. 초음파 진동은 압전소자 (piezoelectric device)에 의해서 얻어지며 50 m 정도의 진동진폭을 얻기 위해 기계적 진동 증폭자인 혼 (horn)을 추가하여 전체 진동 시스템이 공진하도록 구성된다. 음향유동에 의한 열전달 효과의 상승을 측정하기 위해 열원 (heat source) 및 열원 주위의 대기의 온도변화를 실시간으로 측정하였다. 초음파 진동 시작 후 시간지연 없이 음향유동이 유도되어 진동자 주위의 대량의 공기유동으로 인한 급격한 온도감소가 관찰되었다. 또한 열원과 진동자와의 거리가 방사 (radiation)되는 음파 (sound wave)의 반파장 (half wave length)의 정배수가 될 때 열원의 냉각효과가 극대화됨을 실험적으로 관찰하였다. 이는 음파의 공진현상에 기인한 것으로 이론적 고찰을 통한 검증 또한 수행되었다. 음향유동을 이용한 냉각법의 장점은 초음파 진동을 이용하기 때문에 무소음이며 이동 형태의 부품이 없기 때문에 반영구적으로 사용할 수 있다. 또한 기존의 전기모터를 이용한 냉각팬 (cooling fan)으로는 냉각이 어려운 초소형 기전시스템 (MEMS)의 냉각법으로 사용될 수 있는 첨단 냉각방법이다.