• 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.

• Journal of Mechanical Science and Technology
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• 제17권10호
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• pp.1583-1596
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• 2003

A study of forced convection in a circular pipe with a partially filled porous medium was numerically investigated. The Brinkman-Forchheimer extension of the Darcy model was used to analyze the and temperature distribution in the porous medium. Our study includes two types of porous layer configurations: (1) a layer attached at the tube wall extending inward towards the centerline and (2) a layer at the centerline extending outward. The effect of several parameters, such as Darcy number, effective viscosity, effective thermal conductivity, and inertia parameter, as well as the effect of geometric parameters, were investigated.

• 대한기계학회논문집B
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• 제37권8호
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• pp.759-765
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• 2013

동축형 전단 분사기의 액적분포 균일도 및 혼합성능을 개선하기 위해 고안한 액체로켓 엔진용 동축형 다공성 분사기의 개발에 앞서 다공성재를 분사기에 적용하기 위해 다공성재를 통과하는 압축성 유체의 압력강하 특성을 파악하였다. Non-Darcy 유동의 압력강하는 점성력과 관성력으로 인한 손실을 포함하는 Forchheimer 방정식을 이용하여 도출할 수 있으며, 이 때 다공성재의 형상인자인 투과율과 관성력의 영향을 나타내는 Ergun 상수를 이용하여 다공성재를 통과하는 압축성 유체의 압력강하를 예측할 수 있다. 본 연구에서는 다공성재의 압력강하 특성을 나타내는 투과율와 Ergun 상수를 작동유체의 압력강하에 대한 함수로 나타내었으며, 최종적으로 이를 일반화하여 pore의 크기에 따라 압력강하를 예측할 수 있는 관계식을 도출하였다.

• Korean Chemical Engineering Research
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• 제53권6호
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• pp.814-817
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• 2015

A new ionic mass transfer correlation is derived for the fluid-saturated, horizontal porous layer. Darcy-Forchheimer model is used to explain characteristics of fluid motion. Based on the microscales of turbulence a backbone mass transfer relation is derived as a function of the Darcy-Rayleigh number, $Ra_D$ and the porous medium Schmidt number, $Sc_p$. For the Darcy's limit of $Sc_p{\gg}Ra_D$, the Sherwood number, Sh is a function of $Ra_D$ only. However, for the region of high $Ra_D$, Sh can be related with $Ra_DSc_p$. Based on the present backbone equation and the electrochemical mass transfer experiments which are electro plating or electroless plating, the new ionic mass transfer correlation is suggested in the porous media.

• 한국농공학회논문집
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• 제55권6호
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• pp.145-154
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• 2013

Recently, damage occurrence by wind erosion has been increasing in society. In times past, such problems only took place in desert area ; however, in recent years, the wind erosion problem is spreading out to agricultural land. Wind erosion in agricultural land can cause loss of loam soils, the disturbance of the photosynthesis of the crop fields and serious economic losses. To overcome the mentioned problems, installation of windbreak fence can be recommended which function as disturbing strong wind and wind erosion. However, there is still no proper guideline to install the windbreak fence and the installation used to rely on the intuition of the workers due to the lack of related studies. Therefore, this study measured the aerodynamic resistance of screens of the windbreak fence using the apparatus for testing screens. The apparatus for testing screens was designed to measure pressure loss around the screen. Measured pressure loss by wall friction compensated for pressure loss to calculate the aerodynamic resistance of screens. The result of pressure loss by regression analysis derived the aerodynamic coefficient of Darcy-Forchheimer equation and power law equation. The aerodynamic resistance was constant regardless of the overlapped shape when the screen was overlapped into several layers. Increasing the number of layers of the screen, internal resistance increased significantly more, and pressure loss caused by the screen also increased linearly when the wind speed was certain conditions, but permeability had no tendency. In the future, the results of this study will be applied to the computational fluid dynamics simulation. The simulation models will be also validated in advance by wind tunnel experiments. It will provide standard of a design for constructing windbreak fence.

• 전기화학회지
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• 제2권2호
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• pp.98-105
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• 1999

본 연구에서는 전기장에 의하여 유발되는 자연대류의 영향을 줄이기 위하여 수평 다공성 유체층에 열적 성충화를 유지하여 부력과 유체층의 안정화 효과를 체계적으로 조사하였다. 이를 위하여 수평 다공성 유체층에서 이중확산대류에 의한 물질전달 상관식을 이론적으로 유도하고, 전기화학 실험을 통하여 이론에 의한 모델을 보완하였다. 물질전달 상관식은 다공성 매질층에 대한 유동 방정식으로 Forchheimer모델을 사용하고 미세 난류 모델을 적용하여, 용질 및 열 Darcy-Rayleigh수와 Lewis 수로 유도하였다. 실험에서는 다공성매질에 포화된 황산구리황산용액내의 구리이온을 전기 화학적 방법을 통하여 확산 또는 자연대류에 의한 물질전달 실험을 수행하였다. 이론 및 실험적 해석 결과를 종합하면 다공성 매질 내에서 구리이온의 이중확산대류에 의한 물질전달 상관식은 다음과 같다. $$Sh=\frac{0.03054(Rs_D-LeRa_D)^{1/2}}{1-3.8788(Rs_D-LeRa_D)^{-1/10}}$$ 본 연구의 결과는 실험치와 잘 부합되었으며, 모델식의 원형은 열 및 물질전달계에서 자연대류의 영향을 효과적으로 제어할 수 있는 방안으로 활용될 수 있을 것이다.

• 한국해안·해양공학회논문집
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• 제21권1호
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• pp.30-38
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• 2009

최근에 해안구조물의 시공에 있어 친수성 및 방재 기능을 동시에 갖는 구조물이 검토되는 사례가 증가하고 있다. 본 연구의 목적은 비교적 급한 1:5 사면을 가진 해안구조물 위로 전파하는 파랑변형 및 파의 처오름을 예측하는 것이다. 사면 위의 파랑변형 및 처오름을 해석하기 위하여 비선형 천수방정식을 사용하였으며, 투수층 내의 유체운동에는 확장형 Forchheimer의 저항법칙에 근거한 비선형, 비정상 Darcy법칙을 적용하여 규칙파 및 불규칙파를 대상으로 수행되었고, 계산결과는 PBREAK 수치모델의 적용성 및 한계성을 검토하기 위하여 수리모형실험 결과와 비교검토 되었다. PBREAK 수치모델은 사면 위의 파형의 변화를 잘 예측하였으나 질량 및 운동량의 교환이 많이 발생하는 쇄파대 내에서 수리모형실험 결과와 약간의 차이를 보여주었다. 또한 수심평균된 수립자 유속은 파봉 부근을 제외하고 파곡 아래에서 계측한 실험치와 잘 일치하였다.

• 대한기계학회논문집B
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• 제22권4호
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• pp.428-439
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• 1998

Fluid flow and heat transfer have been numerically investigated for an oscillating flow in a tube with a regenerator. The regenerator is placed between hot and cold spaces which are heated and cooled at uniform temperature. An oscillating flow is generated by the piston motion at both ends of a tube. The time dependent, two-dimensional Navier-Stokes equations and energy equation are solved by using the finite-volume and moving grid method. The regenerator is adopted as Brinkmann-Forchheimer extended Darcy model. Numerical results are obtained for the flow and temperature fields, and described the effects of the oscillating frequency and amplitude ratio by the piston motion as well as the aspect ratio. The numerical results obtained indicate that the heat transfer between the tube wall and oscillating flow is increased as the oscillating frequency, amplitude ratio and the aspect ratio are increased.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.112-117
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• 2000

A numerical study on natural convection in a vertical square cavity filled with a porous medium is carried out with Brinkman-Forchheimer-extended Darcy flow model, and the validity of local thermodynamic equilibrium assumption is studied. The local thermodynamic equilibrium refers to the state in which a single temperature can be used to describe a heat transfer process in a multiphase system. With this assumption, the analysis is greatly simplified because only one equation is needed to describe the heat transfer process. But prior to using this assumption, it is necessary to know in what conditions the assumption can be used. The numerical results of this study reveal that large temperature difference between fluid phase and solid phase exists near wall region, paticularily when the convection becomes dominant over conduction. And the influence of flow parameters such as fluid Rayleigh number, fluid Prandtl number, dimensionless particle diameter and conductivity ratio are investigated.

• 대한기계학회논문집
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• 제19권7호
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• pp.1758-1769
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• 1995

The heat transfer of oscillating flow in a cylinder with regenerator was investigated by the moving boundary technique. The flow in regenerator was modeled by means of Brinkman Forchheimer-Extended-Darcy equation . Results showed that when piston moved toward right, velocity vectors near cylinder wall at left piston and right side of regenerator inclined to symmetric axis and velocity vectors near cylinder wall at right piston and left side of regenerator inclined to cylinder wall. And the time averaged Nusselt number was increased by 46.73% when the oscillatory frequency became twice and decreased by 31.46% when the oscillatory frequency became half. The time averaged Nusselt number was increased by 18.09% when thickness of the regenerator became twice and decreased by 7.53% when thickness of the regenerator became half. But mesh size of regenerator hardly affected the Nusselt number. And efficiency of regenerator was larger as the oscillatory frequency was smaller, thickness and mesh size of regenerator was larger.