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채널 내 주기적으로 배열된 요철 형상이 난류 유동장/온도장에 미치는 영향 연구
최도형(D.H. Choi),유동렬(D.N. Ryu),한유신(Y.S. Han) 한국전산유체공학회 2002 한국전산유체공학회 학술대회논문집 Vol.2002 No.-
The heat transfer characteristics of a turbulent flow in a ribbed two-dimensional channel have been investigated numerically. The fully elliptic governing equations, coupled with a four-equation turbulence model, k-ω-t²-ε_t , are solved by a finite volume method of SIMPLE type. Calculations have been carried out for three rib cross-sections: square, triangular, and semicircular, with various rib pitches and Reynolds numbers. The procedure appears to be satisfactory as the results for the square rib compare favorably with available experimental data and earlier calculation. The optimal rib pitch that yields the maximum heat transfer has been identified. It is also found that the square rib is most effective in enhancing the heat transfer. The semicircular rib, on the other hand, incurs the least amount of pressure drop but the improvement in heat transfer is substantially lower.
[論文] 점성-비점성 유동 반복계산 방법을 이용한 2차원 자동차모형의 공력 특성 예측
최도형(D.H.Choi),최철진(C.J.Choi) 한국자동차공학회 1986 오토저널 Vol.8 No.1
An iterative viscous-potential flow procedure has been developed and used to predict aerodynamic characteristics of automobiles in ground proximity. The method is capable of predicting the effects of separated flows. The viscous-potential flow iteration procedure provides the connection between potential flow, boundary layer and wake modules. The separated wake is modeled in the potential flow analysis by thin sheets across which exists a<br/> jump in velocity potential. The ground effect is properly accounted for by placing a body image in the potential flow calculation. The agreement between theory and experiment is good and, thus, demonstrates that the method can be used in the preliminary design stage.
[論文] 자동차 냉각장치를 통하는 유동에 의한 항력 변환 예측
최도형(D.H Choi),이응호(E.H.Lee) 한국자동차공학회 1992 오토저널 Vol.14 No.5
Using a commercial flow-analysis code VSAERO, a method to predict the drag of an automobile induced by the intake air of the cooling system has been devised. Given the pressure loss coefficient across the radiator, which varies with the radiator shape and the local Re, a simplified model of the internal flow is coupled with VSAERO to find the mass-flow rate through the car. The flow rate is obtained iteratively and that, in turn, gives the drag associated with this flow, which essentially is the momentum carried by the drained air. The results of a few sample cases are presented for two front-end shapes in combination with varying radiator frontal area.
전기 화학 반응을 포함한 3차원 열 유동 해석을 이용한 용융탄산염 연료전지의 성능예측
조황묵(H.M. Cho),이경원(K.W. Lee),최도형(D H. Choi) 한국전산유체공학회 2003 한국전산유체공학회 학술대회논문집 Vol.2003 No.-
An analysis procedure for the MCFC channel flow has been developed to predict the fuel cell performance, As for the electrochemical reaction, among several chemical reaction models, one that fits the data best is adopted after a comprehensive comparative study. The Navier-Stokes, energy, and species equations are solved to obtain the velocity, temperature and concentration fields for a specified average current density, The procedure is iterative as the local current density, or the reaction rate, is allowed to vary with the gas composition. A series of calculations are then carried out to examine the effects of gas flow rate, gas composition, gas usage rate, inlet gas temperature, and average current density on the fuel cell performance, The fuel cell characteristics, such as the temperature, current density distributions, and the concentration fields, for various operating conditions are presented and discussed.
내부 manifold를 갖는 MCFC 단위전지 내의 개선된 3차원 열ㆍ유동 해석
김형섭(H. S. Kim),최도형(D. H. Choi) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
An improved three-dimensional numerical analysis for a MCFC stack has been carried out to predict its performance. The continuity, Navier-Stokes, energy, and species equations are solved for the velocity, temperature, pressure and concentration distributions in the cathode and anode channels of a unit cell. The channel with the trapezoidal supports is approximated by an anisotropic porous medium, whose effective permeability and conductivity are obtained by separate 3D FVM calculations.<br/> The diffusion coefficient for each species is evaluated from a simplified formular for multicomponent mixtures. The performance of a unit cell is estimated for a range of loads and utilization rates. This is an iterative process and is assumed to have converged when the cell voltage and the local current density fall within the specified convergence criterion. The fuel cell characteristics, such as the temperature, pressure, mole concentration, voltage and current density distributions, are presented and discussed.
민준기(J.K. Min),최도형(D.H. Choi) 한국전산유체공학회 2000 한국전산유체공학회지 Vol.5 No.1
The LiBr-H₂O absorption process on a horizontal tube has been analyzed numerically. The flow field, which was calculated in the authors' previous study by solving the fully elliptic Navier-Stokes equations with accurate free-surface-tracking method, is used to solve the temperature and concentration distributions in the absorption film. With the assumption that the absorbent is linear, calculations have been made for various inlet temperature and flow-rate conditions. For low inlet temperature, the absorption rate is large in the upstream region but the mean temperature also increases and as a result the absorption decreases as the film flows to downstream while high-inlet-temperature case does the opposite. The difference in the absorption rate due to the inlet temperature change becomes smaller in the downstream than that in the upstream. For large flow rate, the heat transfer to the wall becomes poor due to the thick film and so does the absorption rate. The analyses have also been carried out for multiple tube arrangement and the results show that the absorption rate converges after a few tube rows.
조원국(W.K. Cho),최도형(D.H. Choi),김문언(M.U. Kim) 한국전산유체공학회 1998 한국전산유체공학회 학술대회논문집 Vol.1998 No.-
A numerical optimization procedure is developed to find the inlet velocity profile that yields the most uniform epitaxial layer in a vertical MOCVD reactor. It involves the solution of fully elliptic equations of motion. temperature, and concentration; the finite volume method based on SIMPLE algorithm has been adopted to solve the Navjer-Stokes equations. The overall optimization process is highly nonlinear and has been efficiently treated by the sequential linear programming technique that breaks the non-linear problem into a series of linear ones. The optjmal profile approximated by a 6th-degree Chebyshev polynomial is very successful in reducing the spatial non-uniformity of the growth rote. The optimization is particularly effective to the high Reynolds number flow. It is also found that a properly constructed inlet velocity profile can suppress the buoyancy driven secondary flow and improve the growth-rate uniformity.
최장섭(J.S.Choi),최도형(D.H.Choi),박승오(S.O.Park) 한국자동차공학회 1988 오토저널 Vol.10 No.2
The finite-difference three-dimensional boundary layer procedure of Chang and Patel is modified and applied to solve the boundary layer development on the automobile surface. The inviscid pressure distribution needed to solve the boundary layer equations is obtained by using a low order panel method.The plane of symmetry boundary layer exhibits the strong stream-line divergence up to the midbody and convergence thereafter. The streamline divergence in front of the windshield helps the boundary layer to overcome the severe adverse pressure grad-ient and avoid the separation.The relaxation of the pressure right after the top of the wind-shield, on the other hand, makes the overly thinned boundary layer to readjust and prompts the streamlines to converge into the symmetry plane before the exernal streamllines do.The three-dimensional charateristics are less apparent after the midbody and the boundary layer is similar to that of the two-dimensional flow. The results of the off-plane-of symmentry boundary layer are also presented.
전기화학반응을 포함한 3차원 열·유동해석을 통한 용융탄산염 연료전지의 단위 전지 성능해석
김영록(Y. R. Kim),최도형(D. H. Choi) 한국전산유체공학회 2004 한국전산유체공학회 학술대회논문집 Vol.2004 No.-
An analysis procedure for the MCFC channel flow has been developed to predict the fuel cell performance. The channel formed by the uniformly distributed trapezoidal supports is approximated by the porous medium that yields the equivalent pressure drop. The Navier-Stokes, energy, and species equations are solved to obtain the velocity, temperature and concentration fields for a local current density which is computed from electrochemical correlations. The fuel cell characteristics, such as the temperature, pressure, mole concentration, voltage and current density distributions, are presented and discussed.