• Proceedings of the KSME Conference
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• 2000.11b
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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.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.7
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.7
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• pp.983-990
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• 2002

A numerical analysis has been carried out on forced convection heat transfer in the developing region of a porous channel. The channel is filled with an isotropic porous medium. At the channel walls, a uniform heat flux is given. Comprehensive numerical solutions are acquired to the Brinkman-Forchheimer extended Darcy equation and the LTNE model which does not employ the assumption of local thermal equilibrium between solid and fluid phases. Details of thermal fields in the developing region are examined over wide ranges of the thermal parameters. The numerical solutions at the fully developed region are compared with the previous analytical solutions. The correlation for predicting local Nusselt number in a porous channel is proposed.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.57-64
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• 2000

The present work investigates the heat transfer characteristics for laminar fully developed forced convection in an internally finned tube with axially uniform heat flux and peripherally uniform temperature through analytical models of convection in a porous medium. Using the Brinkman-extended Darcy flow model and the two equation model fur heat transfer, analytical solutions fur fluid flow and heat transfer are obtained and compared with the exact solution for fluid flow and the numerical solutions for conjugate heat transfer to validate the porous medium approach. Using the analytical solutions, parameters of engineering importance are identified and their effects on fluid flow and heat transfer are studied. Also, the expression fur total thermal resistance is derived from the analytical solutions and minimized in order to optimize the thermal performance of the internally finned tubes.

• 한국생물공학회:학술대회논문집
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• 2002.04a
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• pp.489-492
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• 2002

We have performed batch chromatography experiments to calculate parameters which are used to design SMB chromatography system. Isotherms of S- and R-ketoprofen enantiomers were gained from small amount loading experiments in a column, and flow rate of four zones of SMB chromatography were calculated using mass balance equations. As a results, diameter and length of columns were 10mm and 600mm, and flow rate of each zone were as follows; $Q_{Feed}$=1.00ml/min ,$Q_{Elu}$=2.81ml/min ,$Q_{Raf}$=1.81ml/min ,$Q_{Ext}$=2.00ml/min , and $Q_{Rec}^{TMB}$=10.75ml/min , From the Darcy's equation, the pressure drop in whole columns of SMB chromatography was 128bar.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.685-693
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• 1990

The heat transfer coefficients were calculated numerically to see the effects of radiation around the porous medium put on the flat plate at a distance from the leading edge of flat plate for the two-dimensional laminar flows. To verify the analytical model developed and invoke the heat/mass transfer analogy, an experiment was carried out using naphthalene sublimation technique. From the effects of the wake, Sherwood number is maximum around the region where the porous medium is attached. The theoretical results correspond well with the experimental results at small Darcy number. Permeability of ceramic blocks used for experiment was also measured and the Forchheimer equation is applicable in our measurement range.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.7
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• pp.337-343
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• 2015

This paper investigates the ventilation characteristics in a two-dimensional underground network junction composed of four main lines interconnected by eight ramps. Simple one-dimensional models cannot be applied to network junctions since there are interferences of traffic piston effects in the main lines and at the ramps. A numerical algorithm was developed to analyze the pressure and airflow distributions iteratively. The Darcy-Weisbach equation was used to calculate the piston effects by traffic flows, and a Hardy Cross iteration was conducted for network analysis at the interconnected junction. The results show interesting ventilation characteristics and CO concentration distributions depending on system parameters such as vehicle speed, tunnel diameter, and other junction configurations.

• Journal of Korea Water Resources Association
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• v.45 no.1
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• pp.39-52
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• 2012

Surface-subsurface interactions are an intrinsic component of the hydrologic response within a watershed. In general, these interactions are considered to be one of the most difficult areas of the discipline, particularly for the modeler who intends simulate the dynamic relations between these two major domains of the hydrological cycle. In essence, one major complexity is the spatial and temporal variations in the dynamically interacting system behavior. The proper simulation of these variations requires the need for providing an appropriate coupling mechanism between the surface and subsurface components of the system. In this study, an approach for modelling surface-subsurface flow and transport in a fully intergrated way is presented. The model uses the 2-dimensional diffusion wave equation for sheet surface water flow, and the Boussinesq equation with the Darcy's law and Dupuit-Forchheimer's assumption for variably saturated subsurface water flow. The coupled system of equations governing surface and subsurface flows is discretized using the finite volume method with central differencing in space and the Crank-Nicolson method in time. The interactions between surface and subsurface flows are considered mass balance based on the continuity conditions of pressure head and exchange flux. The major module consists of four sub-module (SUBFA, SFA, IA and NS module) is developed.

• Journal of the Korean Society of Safety
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• v.11 no.4
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• pp.143-150
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• 1996

This is an explicit-Implicit, finite element analysis for linear as well as nonlinear hygrothermal stress problems. Additional features, such as moisture diffusion equation, crack element and virtual crack extension(VCE ) method for evaluating J-integral are implemented in this program. The Linear Elastic Fracture Mechanics(LEFM) Theory is employed to estimate the crack driving force under the transient condition for and existing crack. Pores in materials are assumed to be saturated with moisture in the liquid form at the room temperature, which may vaporize as the temperature increases. The vaporization effects on the crack driving force are also studied. The Ideal gas equation is employed to estimate the thermodynamic pressure due to vaporization at each time step after solving basic nodal values. A set of field equations governing the time dependent response of porous media are derived from balance laws based on the mixture theory Darcy's law Is assumed for the fluid flow through the porous media. Perzyna's viscoplastic model incorporating the Von-Mises yield criterion are implemented. The Green-Naghdi stress rate is used for the invariant of stress tensor under superposed rigid body motion. Isotropic elements are used for the spatial discretization and an iterative scheme based on the full newton-Raphson method is used for solving the nonlinear governing equations.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.4
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• pp.101-109
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• 1993

On the basis of Nikuradse laboratory experiments. two transition flow regimes are defined with respect to the characteristics of boundary layer. One is the transitional turbulent flow which has a transitional characteristics between smooth turbulent flow and rough turbulent flow, and the other may be called as transitional laminar flow which has transitional features between laminar flow and turbulent flow. The laboratory results of Nikuradse are carefully re-examined, and the flow regions are clearly defined. The velocity profile of the transitional turbulent flow is described by newly formulated equation, and the Darcy-Weisbach friction coefficient for the transitional turbulent flow is determined based on the theoretical form of profile equation, which is far better accurate than Colebrook-White equation. Difficulties still arise for the description of velocity profile when the flow undergoes from laminar to turbulent. In this case a linear interpolation procedure is proposed for the estimation of friction coefficient.