• 제목/요약/키워드: tube theory

검색결과 251건 처리시간 0.028초

마이크로관 내 압력강하 특성 및 상관식에 관한 연구 (Pressure Drop in Microtubes and Correlation Development)

  • 황윤욱;김주혁;김민수
    • 설비공학논문집
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    • 제18권1호
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    • pp.38-46
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    • 2006
  • The characteristics about the pressure drop in microtubes have been investigated. The test tubes are the circular, seamless, stainless steel tubes with an inner diameter of 0.244, 0.430, and 0.792 mm, respectively. R-l34a was used as a test fluid. Early flow transition which has been reported in some previous studies is not found in single-phase flow pressure drop tests. The conventional theory between friction factor and Reynolds number predicted the experimental friction factors within an absolute average deviation of $8.9\%$. The two-phase flow pressure drop increases for higher quality and mass flux, and for reduced inner diameter. The existing correlations fail to predict the experimental data. A new correlation to predict the two-phase flow pressure drop is developed in the form of the Lockhart-Martinelli correlation. The effects of the tube diameter and the surface tension were considered, and the correlation predicted the experimental data within an average absolute deviation of $8.1\%$.

단일 E-평면구조를 이용한 협대역 도파관형 대역통과 여파기의 설계 (Design of Narrow-band Waveguide Bandpass Filters Using Single E-Plane Structures)

  • 박준석;임재봉;김철동
    • 한국전자파학회지:전자파기술
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    • 제6권2호
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    • pp.35-44
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    • 1995
  • 본 논문에서는 우수한 양산성을 감안한 협대역 도파관형 대역통과 여파기를 제작하기 위하여 미리 제작된 판 재를 도파관 튜브의 내부에 파진 스롯에 끼워넣는 단일 E 평면구조를 제안하고, 이를 변분해석볍을 사용하여 해석하였다. 그리고 통과대역 보정법에 의한 여파기 합성설계방볍을 사용하여 마이크로파대 협대역 도파관형 대역통과 여파기를 설계하는 CAD 프로그램을 개발하였다. 개발된 프로그램으로 중심주파수 3.82GHz 5단 O.002dB equi-ripple Chebyshev형 28MHz의 대역폭을 갖는 대역통과 여파기를 설계하여 튜닝구조로 제작, 여파기 특성을 미세조정과정을 거쳐 실험하였다. 그 결과 이론치와 잘 일치하는 측정결과를 얻었다.

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열음향 공진 점화에 대한 연구 (Research about Thermoacoustic Resonance Ignition)

  • 서성현;강상훈;배종열;이진영
    • 한국추진공학회지
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    • 제20권1호
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    • pp.82-89
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    • 2016
  • 초음속 유동의 운동에너지가 열에너지로 바뀌는 열음향 공진 현상을 활용하여 액체로켓엔진의 다중 점화를 위한 점화기 구현에 적용할 수 있다. 본 논문은 이와 같은 열음향 공진 현상의 기본 원리와 이론, 현재까지 진행된 주요 연구결과를 본문에 수록하였다. 열음향 공진 현상에 의한 열발생 특성은 초음속 노즐을 통해 분출되는 유동의 특성과 노즐과 공진관의 형상 그리고 에너지를 전달하는 기체의 종류에 의해 영향 받는다. 이와 같은 열음향 공진 현상을 적용한 액체로켓엔진을 위한 다중 점화기를 구성하는데 있어서 향후 연구 개발이 필요한 부분에 대한 논의를 진행하였다.

ENHANCEMENT THE SOUND TRANSMISSION LOSS OF POROELASTIC LININGS

  • Song, B.Heuk-Jin;Bolton, J.Stuart
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2000년도 춘계학술대회논문집
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    • pp.606-611
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    • 2000
  • It has been noted that the low frequency absorption coefficient of a porous sample placed in a standing wave tube is affected by the nature of the sample's edge constraint. The edge constraint has the effect of stiffening the solid phase of the sample, which itself can be strongly coupled to the material's fluid phase, and hence the incident sound field, by viscous means at low frequencies. In recent work it has also been shown that such a circumferential constraint causes the low frequency transmission loss of a layer of fibrous material to approach a finite low frequency limit that is proportional to the flow resistance of the layer and which is substantially higher than that of an unconstrained sample of the same material. However, it was also found that the benefit of the circumferential edge constraint was reduced in a transitional frequency range by a shearing resonance of the sample. Here it will be shown that the effect of that resonance can be mitigated or eliminated by adding additional axial and radial constraints running through the sample. It will also be shown that the constraint effect can be modeled closely by using a finite element procedure based on the Biot poroelastic theory. Implications for low frequency barrier design are also discussed.

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Malaysia's 13th General Election: Political Communication and Public Agenda in Social Media

  • Sern, Tham Jen;Zanuddin, Hasmah
    • Asian Journal for Public Opinion Research
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    • 제1권2호
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    • pp.73-89
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    • 2014
  • Everyone has a voice and can broadcast it to the world. We hear about the old maxim of media do not tell people what to think but what to think about. Under this theory or approach, a key function of political communication is to make the public think about an issue in a way that is favorable to the sender of the message. In a democracy, political communication is seen as crucial for the building of a society where the state and its people feel they are connected. Thus, this is a study on how social media (e.g., Facebook, blogs, and YouTube) were used in the domain of Malaysian politics during the 13th general election campaigning period in order to set the agenda to form public opinion. The study found that Facebook was the most popular social media tool that political parties actively engaged with during the 13th general election campaign period. Apart from that, issues pertaining to the election were significantly highlighted by the political parties in social media, especially Facebook. However, other issues that were also important to the people such as the economy, crime, and education were not sufficiently highlighted during the election campaign period. This indicates that the political parties influence the public on what to think about using social media.

Theoretical impact of Kelvin's theory for vibration of double walled carbon nanotubes

  • Hussain, Muzamal;Naeem, Muhammad N.;Asghar, Sehar;Tounsi, Abdelouahed
    • Advances in nano research
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    • 제8권4호
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    • pp.307-322
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    • 2020
  • In this article, free vibration of double-walled carbon nanotubes (DWNT) based on nonlocal Kelvin's model have been investigated. For this purpose, a nonlocal Kelvin's model is established to observe the small scale effect. The wave propagation is employed to frame the governing equations as eigenvalue system. The influence of nonlocal parameter subjected to different end supports has been overtly examined. The new set of inner and outer tubes radii investigated in detail against aspect ratio. The influence of boundary conditions via nonlocal parameter is shown graphically. Due to small scale effect fundamental frequency ratio decreases as length to diameter ratio increases. Small scale effect becomes negligible on all end supports for the higher values of aspect ratio. With the smaller inner tube radius double-walled CNT behaves more sensitive towards nonlocal parameter. The results generated furnish the evidence regarding applicability of nonlocal model and also verified by earlier published literature.

히트파이프와 용융염을 사용하는 태양열 축열조의 설계 (Design of a Solar Thermal Storage System Employing Heat Pipes and Molten Salts)

  • 이정륜;부준홍
    • 한국태양에너지학회:학술대회논문집
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    • 한국태양에너지학회 2011년도 춘계학술발표대회 논문집
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    • pp.86-91
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    • 2011
  • Thermal design was conducted for a solar thermal storage system in a medium-temperature range between $200^{\circ}C$ and $400^{\circ}C$. The system was composed of heat pipes as heat carrier and molten salts as phase-change storage material. Each heat pipe penetrated through the storage system and had two heat-exchanging sections at both ends to interact with high-and low-temperature steams, while it exchanged heat with molten salts in the middle section. During a heat-storage mode, the heat pipes transferred heat from the hot steam at one side to the molten salts and it transferred heat from the molten salt to the cold steam at the other side during the heat-dissipating mode. A tube-bank type heat exchanger theory was applied to this design task to meet the required inlet and outlet temperatures of the steams depending on the operation modes. Several design variables were considered including the lengths of evaporator and condenser of a heat pipe, traverse and longitudinal pitches of the pipe, and the number of rows of the heat pipes for two different molten salt baths. An optimum design results were presented with discussion.

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열응답 시험과 변수 평가 모델을 이용한 그라우트/토양 혼합층의 열전도도 산정 (Evaluation of Thermal Conductivity for Grout/Soil Formation Using Thermal Response Test and Parameter Estimation Models)

  • 손병후;신현준;안형준
    • 설비공학논문집
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    • 제17권2호
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    • pp.173-182
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    • 2005
  • The Performance of U-tube ground heat exchanger for geothermal heat Pump systems depends on the thermal properties of the soil, as well as grout or backfill materials in the borehole. In-situ tests provide a means of estimating some of these properties. In this study, in-situ thermal response tests were completed on two vertical boreholes, 130 m deep with 62 mm diameter high density polyethylene U-tubes. The tests were conducted by adding a monitored amount of heat to water over a $17\~18$ hour period for each vertical boreholes. By monitoring the water temperatures entering and exiting the loop and heat load, overall thermal conductivity values of grout/soil formation were determined. Two parameter estimation models for evaluation of thermal response test data were compared when applied on the same temperature response data. One model is based on line-source theory and the other is a numerical one-dimensional finite difference model. The average thermal conductivity deviation between measured data and these models is of the magnitude $1\%$ to $5\%$.

언덕지형을 지나는 유동에 관한 연구 (Wind Flow over Hilly Terrain)

  • 임희창;김현구;이정묵;경남호
    • 한국대기환경학회지
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    • 제12권4호
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    • pp.459-472
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    • 1996
  • An experimental investigation on the wind flow over smooth bell-shaped two-dimensional hills with hill slopes (the ratio of height to half width) of 0.3 and 0.5 is performed in an atmospheric boundary-layer wind tunnel. Two categories of the models are used in the present investigation; six two-dimensional single-hills, and four continuous double-hills. The measurements of the flow field and surface static-pressure distribution are carried out over the Reynolds number (based on the hill height) of 1.9 $\times 10^4, 3.3 \times 10^4, and 5.6 \times 10^4$. The velocity profiles and turbulence characteristics are measured by the pitot-tube and X-type hot-wire anemometer, respectively. The undisturbed boundary-layer profile on the bottom surface of the wind tunnel is reasonably consistent with the power-law profile with $\alpha = 7.0 (1/\alpha$ is the power-law exponent) and shows good spanwise uniformities. The profiles of turbulent intensity are found to be consistent along the centerline of the wind tunnel. The measured non-dimensional speed-up profiles at the hill crest show good agreements with the predictions of Jackson and Hunt's linear theory. The flow separation occurs in the hill slope of 0.5, and the oil-ink dot method is used to find the reattachment points in the leeside of the hill. The measured reattachment points are compared with the numerical predictions. Comparisons of the mean velocity profiles and surface pressure distributions between the numerical predictions and the experimental results show good agreements.

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Performance evaluation of bubble pump used on solar water heating system

  • Xuesong, Li;Park, Gi-Tae;Kim, Pil-Hwan;Chung, Han-Shik;Jeong, Hyo-Min
    • 대한설비공학회:학술대회논문집
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    • 대한설비공학회 2007년도 동계학술발표대회 논문집
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    • pp.416-422
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    • 2007
  • The application analysis of bubble pump on the domestic solar water heater system is presented. The system investigated in this study is a passive device, self pumping and self regulating. It was test to use the bubble pump on solar water heater system. The test experiment has been taken on the existed vacuum tube about the efficiency, working fluid temperature and pressure and circulated power. In order to check the working temperature and working pressure effectively, the bubble pump was test separated from the solar water heater. The equipment consists of the bubble pump, heater and heat exchanger. The main structure of bubble pump was design depend on the character of two phase flow. The complete system was instrumented to measure pressures, temperatures and their relationship with the solar radiation intensity. The theory analysis of design bubble pump has been given and the experiment result analysis has been included in the paper.

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