• 제목/요약/키워드: Vertical Convection

검색결과 271건 처리시간 0.023초

수직$\cdot$수평 관통류를 갖는 수평 다공층에서 자연대류 연구 (The Natural Convection in Horizontal Porous Layer with Vertical or Horizontal Throughflow)

  • 서석진;박찬국
    • 한국전산유체공학회지
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    • 제3권1호
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    • pp.73-81
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    • 1998
  • The effect of vertical or horizontal throughflow on natural convection in horizontal porous layer was investigated. The computations were performed by employing Darcy-Brinkman-Forchheimer equation to consider the effect of inertia and viscous effect. The patterns of streamlines and isotherms are observed by changing the strength of throughflow. The vertical throughflow stabilizes the natural convection in porous layer. It also disturbs the developing vertical and horizontal velocity component of natural convection cell and increases the critical modified Rayleigh number. The horizontal throughflow influences the stabilization of natural convection in porous layer much more than the vertical throughflow. And it changes a stable convection into a oscillatory convection.

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수직 동심 환형관 내의 난류혼합대류 현상에 관한 직접수치모사 (Direct Numerical Simulation of Turbulent Mixed Convection in Heated Vertical Annulus)

  • 전용준;배중헌;유정열
    • 대한기계학회논문집B
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    • 제33권9호
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    • pp.674-681
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    • 2009
  • Turbulent mixed convection in heated vertical annulus is investigated using Direct Numerical Simulation (DNS) technique. The objective of this study is to find out the effect of buoyancy on turbulent mixed convection in heated vertical annulus. Downward and upward flows with bulk Reynolds number 8500, based on hydraulic diameter and mean velocity, have been simulated to investigate turbulent mixed convection by gradually increasing the effect of buoyancy. With increased heat flux, heat transfer coefficient first decreases and then increases in the upward flow due to the effect of buoyancy, but it gradually increases in downward flow. The mean velocity and temperature profiles can not be explained by the wall log laws due to the effect of buoyancy, too. All simulation results are in good quantitative agreement with existing numerical results and in good qualitative agreement with existing experimental results.

수직 동심 환형관 내의 난류혼합대류 현상에 관한 직접수치모사 (Direct numerical simulation of turbulent mixed convection in heated vertical annulus)

  • 전용준;배중헌;유정열
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2008년도 추계학술대회B
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    • pp.2759-2764
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    • 2008
  • Turbulent mixed convection in heated vertical annulus is investigated using Direct Numerical Simulation (DNS) technique. The objective of this study is to find out the effect of buoyancy on turbulent mixed convection in heated vertical annulus. Downward and upward flows with bulk Reynolds number 8500, based on hydraulic diameter and mean velocity, have been simulated to investigate turbulent mixed convection by gradually increasing the effect of buoyancy. With increased heat flux, heat transfer coefficient first decreases and then increases in the upward flow due to the effect of buoyancy, but it gradually increases in downward flow. The mean velocity and temperature profiles can not be explained by the wall log laws due to the effect of buoyancy, too. All simulation results are in good quantitative agreement with existing numerical results and in good qualitative agreement with existing experimental results.

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일정 열유속으로 가열되는 수직원통 주위의 유체에서의 자연대류에 관한 연구 (On the Study of the Natural Convection in the Fluid near a Vertical Cylinder Heated with Uniform Heat Flux)

  • 이철재;김시범
    • 대한설비공학회지:설비저널
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    • 제17권4호
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    • pp.426-434
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    • 1988
  • Series expansion is applied to solve the laminar boundary layer equations for the problem of natural convection from vertical cylinder with uniform surface heat flux. The series in terms of transverse curvature parameter ${\xi}$ is extended to five terms and is well converged by applying the Shanks transform twice. In case of natural convection from a vertical cylinder heated with uniform surface heat flux, it is possible to consider the vertical cylinder as vertical plate under the condition of D/L${\geq}$A/$(Gr_L^*)^{1/5}$, where A is in the range of 5.7~55.2. Also, mean Nusselt number ${\overline{Nu_L}}$ can be represented as $C_1(Ra_L^*)^{1/5}$, where $C_1$ is a constant which depends on Pr and is in the range of 0.5~0.8.

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종방향대류 및 고액밀도차가 고려된 접촉융해에 대한 해석해 (An analytical solution for the close-contact melting with vertical convection and solid-liquid density difference)

  • 유호선;홍희기;김찬중
    • 대한기계학회논문집B
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    • 제21권9호
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    • pp.1165-1173
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    • 1997
  • The steady state close-contact melting phenomenon occurring between a phase change material and an isothermally heated flat plate with relative motion is investigated analytically, in which the effects of vertical convection in the liquid film and solid-liquid density difference are incorporated simultaneously. Not only the scale analysis is conducted to estimate a priori qualitative dependence of system variables on characteristic parameters, but also an analytical solution to a set of simplified model equations is obtained to specify the effects under consideration. These two results are consistent with each other, in that the vertical convection affects both the solid descending velocity and the film thickness, and that the density difference alters only the solid descending velocity. While the effect of vertical convection can be characterized conveniently by a newly introduced temperature gradient factor which asymptotically approaches the unity/zero with decreasing/increasing the Stefan number, that of density difference is represented by the liquid-to-solid density ratio. It is shown that the solid descending velocity depends linearly on the density ratio, and that the ratios of solid descending velocity, film thickness and friction coefficient to the conduction solution are proportional to 3/4, 1/4 and -1/4 powers of the temperature gradient factor, respectively. Also, established is the fact that the effect of convection can be legitimately neglected in the analysis for the range of the Stefan number less than 0.1.

수직관내 발달 유동의 층류혼합대류 연구 (Study on Laminar Mixed Convection of Developing Flow in Vertical Pipe)

  • 고봉진;정범진
    • 대한기계학회논문집B
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    • 제34권5호
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    • pp.481-489
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    • 2010
  • 수직관내 발달 유동의 층류혼합대류에 관한 본 연구는 Re 1,000에서 3,000, $Gr_H\;10^5$에서 $10^8$, Pr 2,000 에서 7,000 그리고 종횡비 1부터 7에 대한 범위에 대해서 수행되었다. 유사성(Analogy)의 원리를 이용하여 수직관내 발달 유동의 층류혼합대류 열전달계를 물질전달계로 모사하였다. 물질전달계로써 Nu 수는 기존의 문헌들의 그것들보다 상당히 큰 값이었는데, 이는 본 실험의 높은 Pr 수 때문이다. 본 연구에서의 종횡비는 완전발달 할 만큼 크지 않았기 때문에, 실험 결과는 긴 수직관내 혼합대류 유동보단 평행평판에서의 혼합대류 유동과 유사하였다. 본 연구의 결론으로서 낮은 종횡비와 $Gr_H$ 수를 갖는 수직관내 발달 유동의 층류혼합대류 유동은 수직 평판에서의 층류혼합대류 유동과 유사한 거동을 보인다는 것이다. 그리고 종횡비와 $Gr_H$ 수가 증가할 때 유체의 거동은 수직관내 완전발달 유동과 유사한 현상을 보였다.

Influence of thermo-physical properties on solutal convection by physical vapor transport of Hg2Cl2-N2 system: Part I - solutal convection

  • Kim, Geug-Tae;Kim, Young-Joo
    • 한국결정성장학회지
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    • 제20권3호
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    • pp.125-132
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    • 2010
  • For typical governing dimensionless parameters of Ar = 5, Pr = 1.16, Le = 0.14, Pe = 3.57, Cv = 1.02, $Gr_s=2.65{\times}10^6$, the effects of thermo physical properties such as a molecular weight, a binary diffusivity coefficient, a partial pressure of component B on solutally buoyancy-driven convection (solutal Grashof number $Gr_s=2.65{\times}10^6$) are theoretically investigated for further understanding and insight into an essence of solutal convection occurring in the vapor phase during the physical vapor transport of a $Hg_2Cl_2-N_2$ system. The solutally buoyancy-driven convection is significantly affected by any significant disparity in the molecular weight of the crystal components and the impurity gas of nitrogen. The solutal convection in a vertical orientation is found to be more suppressed than a tenth reduction of gravitational accelerations in a horizontal orientation. For crystal growth parameters under consideration, the greater uniformity in the growth rate is obtained for either solutal convection mode in a vertical orientation or thermal convection mode in horizontal geometry. The growth rate is also found to be first order exponentially decayed for $10{\leq}P_B{\leq}200$ Torr.

기복을 이루는 수직벽에서 비뉴턴유체의 자연대류에 관한 연구 (A study of natural convection in non-Newtonian fluids induced by a vertical wavy surface)

  • 김은필
    • 대한기계학회논문집B
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    • 제20권11호
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    • pp.3686-3694
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    • 1996
  • A numerical investigation of natural convection flow along irregular vertical surfaces is reported. A transformation method is applied to the problem of natural convection under the assumption of a large Grashof number. A vertical wavy surface is used as an example to demonstrate the advantages of the transformation method, and to show the heat transfer mechanism near such surfaces. Surface non-uniformities on the boundary layer flow induced by a constant was temperature, semi-infinite surface are investigated. Also the effects of Prandtl number, flow index, and surface amplitude in Non-Newtonian fluids are discussed. When possible, the comparison of the numerical results shows a good agreement. The amplitude is proportional to the amplitude of a wavy surface. The results demonstrate that the local heat flux along a wavy surface is smaller than that of a flat surface. The frequency of the wavy surface is half that of the local heat transfer rate. The amplitude of the local Nusselt number gradually decreases downstream where the natural convection boundary layer grows thick.

격판을 가진 수평환상공간에서의 자연대류 열전달 (Natural Convection Heat Transfer from a Horizontal Annulus with Spacers)

  • 이범철;정한식;권순석
    • 대한기계학회논문집
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    • 제13권1호
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    • pp.153-160
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    • 1989
  • 본 연구는 수평전도관과 수평원통 사이의 환상공간에 수직격판이 부착된 경우와 수평직판이 부착된 경우에 Rayleigh수와 무차원 관열전도율을 변수로하여 수직해석과 Mach-Mehnder 간섭계를 이용한 실험으로 자연대류 열전달특성을 연구 하였다.

Vertical arrangement of coils for efficient cargo tank heating

  • Magazinovic, Gojko
    • International Journal of Naval Architecture and Ocean Engineering
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    • 제11권2호
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    • pp.662-670
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    • 2019
  • Tanker cargo tanks are equipped with the means of raising and maintaining the cargo discharge temperature to a suitable level. In this paper, a new heating coil design is proposed and analyzed. Contrary to conventional designs, wherein the heating coils are evenly distributed over the tank bottom, the proposed design arranges the heating coils in the central part of the tank bottom, in a vertical direction. Due to the intensive cargo circulation generated, a forced convection is superimposed on a buoyancy-driven natural convection, providing a more efficient mixed convection heat transfer mechanism. Numerical simulations performed by using a finite volume method show that in the case of 7-bar steam Bunker C heavy fuel oil heating, a five-hour circulation phase average heat transfer coefficient equals 199.2 W/m2K. This result might be taken as an impetus for the more thorough experimental examination.