• Title/Summary/Keyword: Sinusoidal Wall Temperature Distribution

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Heat Transfer by an Oscillating Flow in a Circular Pipe with Sinusoidal Wall Temperature Distributions (벽온도분포가 정현파인 원관에서 왕복유동에 의한 열전달 해석)

  • 이대영;박상진;노승탁
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.12
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    • pp.3208-3216
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    • 1993
  • Heat transfer characteristics of the laminar oscillating flow in a circular pipe have been studied under the condition that the wall temperature of the pipe is distributed sinusoidally with the axial direction. The axial velocity was assumed to be uniform in radial direction and the temperature field was analyzed by means of the perturbation method. The results show that the difference between wall and section-time-averaged fluid temperature increases as the oscillating frequency increases and eventually converges to a constant value which is determined by the ratio of swept distance to the characteristic length of wall temperature distribution. Also it is shown that the dominant variable in the heat transfer process when swept distance ratio is greater than 1 is not thermal Womersley number(F) but thermal Womersley number multiplied by the square root of swept distance ratio. The variation of the time-averaged Nusselt number is obtained as a function of F. The results indicate that Nusselt number is proportional to $F_{\epsilon}^{1/2}$ when both of F and .epsilon. are much greater than 1.

A new formulation for unsteady heat transfer of oscillatory flow in a circular tube (원관내 왕복유동에서 비정상 열전달 관계식의 공식화)

  • Park, Sang-Jin;Lee, Dae-Yeong;No, Seung-Tak
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.9
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    • pp.2953-2964
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    • 1996
  • Heat Transfer with periodic fluctuation of fluid temperature caused by oscillatory flow or compression expansion can be out of phase with balk fluid-wall temperature difference. Newton's law of convection is inadequate to describe this phenomenon. In order to solve this problem the concept of the complex Nusselt number has been introduced by severla researchers. The complex Nusselt number expresses out of phase excellently while the first harmonic is dominant in the variations of both fluid-wall temperature difference and heat flux. However, in the case of oscillatory flow with non-linear wall temperature distribution, the complex Nusselt number is not appropriate to predict the heat transfer phenomena since the higher order harmonic components appear in periodic temperature variation. Analytic solutions to the heat transfer with an sinusoidal well temperature distribution were obtained to investagate the effect of non-linear wall temperature distribution. A new formula considering the thermal boundary layer was suggested based on the solutions. A comparison was also made with the complex Nusselt number. It was verified that the new formula describes well the heat transfer of oscillating flow even if the first harmonic component is not dominant in the fluid-wall temperature difference.

Heat Transfer by Liminar Oscillating Pipe Flow in Thermally Developing Region (원관내 층류 왕복유동에 의한 열적발달영역에서의 열전달)

  • 이대영;박상진;노승탁
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.4
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    • pp.997-1008
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    • 1994
  • Heat transfer by laminar oscillating flow in a circular pipe has been studied analytically. The general solution with respect to the arbitrary wall boundary condition is obtained by superposing the fluid temperatures with the sinusoidal wall temperature distributions. The fulid temperature distributions are two dimensional, but uniform flow assumption is used to simplify the velocity distribution. The heat transfer characteristics in the thermally developing regions are analyzed by applying the general solution to the two cases of thermal boundary conditions in which the wall temperature and wall heat flux distributions have a square-wave form, respectively. The results show that the length of the thermally developing region becomes larger in proportion to the oscillation frequency at slow oscillation and eventually approaches to the value comparable to the swept distance as the frequency increases. The time and cross-section averaged Nusselt number in the developing region is inversely proportional to the square root of the distance from the position where the wall boundary condition is changed suddenly. In the developed region, Nusselt number is only determined by the oscillation frequency.