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루프 환기구에 따른 보일러빌딩 내부 환기성능에 관한 수치적 연구
최훈기 ( Hoon Ki Choi ),유근종 ( Geun Jong Yoo ),이상헌 ( Sang Heon Lee ) 한국산업보건학회 (구 한국산업위생학회) 2016 한국산업보건학회지 Vol.26 No.3
Objectives: The objective of this paper is to find flow and heat transfer characteristics numerically in boiler buildings for three different ventilation window configurations. Methods: Turbulent natural convection flow in boiler buildings with a constant heating wall temperature was analyzed numerically . Governing equations were solved with standard finite-volume method using the SIMPLE algorithm. Conclusions: Flow and heat transfer characteristics are found for three different ventilation types. In the lower area under furnace, velocity and temperature distributions show similar patterns among the three different ventilation types. In the upper area over furnace, however, air flow is well mixed with lower peak temperatures for types B and C, which have roof ventilation windows, compared to type A which has side wall louvers only. Also, type B, with a single large roof window, shows better ventilation effect than does type C with its distribution roof windows.
최훈기(Hoon Ki Choi),유근종(Geun Jong Yoo) 한국전산유체공학회 2014 한국전산유체공학회지 Vol.19 No.3
In this paper, hydraulic & thermal developing and fully developed laminar forced convection flow of a water-Al₂O₃ nanofluid in a circular horizontal tube with uniform heat flux at the wall, are investigated numerically. A single phase model employed with temperature independent properties. The thermal entrance length is presented in this paper. The variations of the convective heat transfer coefficient and shear stress are shown in the entrance region and fully developed region along different nanoparticles concentration and Reynolds numbers. Convective heat transfer coefficient for nanofluids is larger than that of the base fluid. It is shown that heat transfer is enhanced and shear stress is increased as the particle volume concentration increases. The heat transfer improves, as Reynolds number increases.
최훈기(Hoon-Ki Choi),임윤승(Yun-Seung Lim) 한국기계가공학회 2021 한국기계가공학회지 Vol.20 No.6
We compared the heat transfer characteristics of the parallel and the counterflow flow in the concentric double tube of the Al₂O₃/water nanofluids using numerical methods. The high- and low-temperature fluids flow through the inner circular tube and the annular tube, respectively. The heat transfer characteristics according to the flow direction were compared by changing the volume flow rate and the volume concentration of the nanoparticles. The results showed that the heat transfer rate and overall heat transfer coefficient improved compared to those of basic fluid with increasing the volume and flow rate of nanoparticles. When the inflow rate was small, the heat transfer performance of the counterflow was about 22% better than the parallel flow. As the inflow rate was increased, the parallel flow and the counterflow had similar heat transfer rates. In addition, the effectiveness of the counterflow increased from 10% to 22% rather than the parallel flow. However, we verified that the increment in the friction factor of the counterflow is not large compared to the increment in the heat transfer rate.
Evaluation of the K-Epsilon-VV-F Turbulence Model for Natural Convection in a Rectangular Cavity
최석기(Seok-Ki Choi),김성오(Seong-O Kim),김의광(Eui-Kwang Kim),최훈기(Hoon-Ki Choi) 한국전산유체공학회 2002 한국전산유체공학회지 Vol.7 No.4
The primary objective of the present study is evaluation of the k-ε-vv-f turbulence model for prediction of natural convection in a rectangular cavity. As a comparative study, the from-layer k-ε model is also considered. Both models, with and without algebraic heat flux model, are applied to the analysis of natural convection in a rectangular cavity. The performances of turbulence models are investigated through comparison with available experimental data. The predicted results of vertical velocity component, turbulent heat fluxes, turbulent shear stress, local Nusselt number and wall shear stress are compared with experimental data. It is shown that, among the turbulence models considered in the present study, the k-ε-vv-f model with an algebraic heat flux model predicts best the vertical mean velocity and velocity fluctuation, and the inclusion of algebraic heat flux model slightly improves the accuracy of results.
최석기(Seok-Ki Choi),김성오(Seong-O Kim),김의광(Eui-Kwang Kim),어재혁(Jae-Hyuk Eoh),최훈기(Hoon-Ki Choi) 한국전산유체공학회 2002 한국전산유체공학회 학술대회논문집 Vol.2002 No.-
A numerical study has been performed for evaluation of convection schemes for thermal hydraulic analysis in a liquid metal reactor. Four convection schemes, HYBRID, QUICK, SMART and HLPA included in the CFX -4 code are considered. The performances of convection schemes are evaluated by applying them to the five test problems. The accuracy, stability and convergence are tested. It is shown that the HYBRID scheme is too diffusive, and the QUICK scheme exhibits overshoots and undershoots, and the SMART scheme shows convergence oscillations, and the HLPA scheme preserves the boundedness without causing convergence oscillations. The accuracies of SMART, QUICK and HLPA schemes are comparable. Thus, the use of HLPA scheme is highly recommended for thermal hydraulic analysis in a liquid metal reactor.
바디포오스가 큰 유동에서 운동량보간법의 사용에 관한 연구
최석기(Seok-Ki Choi),김성오(Seong-O Kim),최훈기(Hoon-Ki Choi) 한국전산유체공학회 2002 한국전산유체공학회지 Vol.7 No.2
A numerical study on the use of the momentum interpolation method for flows with a large body force is presented. The inherent problems of the momentum interpolation method are discussed first. The origins of problems of the momentum interpolation methods are the validity of linear assumptions employed for the evaluation of the cell-face velocities, the enforcement of mass conservation for the cell-centered velocities and the specification of pressure and pressure correction at the boundary. Numerical experiments are performed for a typical flow involving a large body force. The numerical results are compared with those by the staggered grid method. The fact that the momentum interpolation method may result in physically unrealistic solutions is demonstrated. Numerical experiments changing the numerical grid have shown that a simple way of removing the physically unrealistic solution is a proper grid refinement where there is a large pressure gradient. An effective way of specifying the pressure and pressure correction at the boundary by a local mass conservation near the boundary is proposed, and it is shown that this method can effectively remove the inherent problem of the specification of pressure and pressure correction at the boundary when one uses the momentum interpolation method.
최석기(Seok-Ki Choi),김성오(Seong-O Kim),최훈기(Hoon-Ki Choi) 한국전산유체공학회 2002 한국전산유체공학회지 Vol.7 No.2
This paper presents the numerical methodology of ATHOS3 code for thermal hydraulic analysis of steam generators in nuclear power plant. Topics include porous media approach, governing equations, physical models and correlations for solid-to-fluid interaction and heat transfer, and numerical solution scheme. The ATHOS3 code is applied to the thermal hydraulic analysis of steam generator in the Korea Karl Unit-l nuclear power plant and the computed results are presented.
조성원(Sung-Won Jo),최훈기(Hoon-Ki Choi),박용갑(Yong-Gap Park) 한국기계가공학회 2022 한국기계가공학회지 Vol.21 No.11
The laminar mixed convection of a nanofluid consisting of water and Al₂O₃ in a horizontal curved tube was numerically studied. Three-dimensional elliptic governing equations were solved to show the manner in which nanoparticle concentration affects thermal and hydrodynamic parameters, which are impressed by centrifugal and buoyancy forces. The effects of nanoparticle volume concentration and the Richardson number on the velocity vector, temperature contour, convective heat transfer coefficient, and pressure drop are presented and discussed. The results showed that at a given Reynolds number, increasing the solid nanoparticle volume concentration and Richardson number increased the convective heat transfer coefficient. In addition, the pressure drop in the pipe significantly increased with an increase in nanoparticle volume concentration.
안내덕트 내부 난류유동구조에 따른 열전달 특성변화 수치해석
유근종(Geun Jong Yoo),최훈기(Hoon Ki Choi),최기림(Kee Lim Choi) 대한기계학회 2011 大韓機械學會論文集B Vol.35 No.9
본 연구에서는 복합화력발전소 가스터빈 출구가스 안내덕트 내부의 가스유동장이 배열회수보일러 전열기구에 미치는 영향을 CFD기법을 이용하여 분석하였다. 안내덕트 내부 난류흐름의 경우, 유속의 편차가 크고 선회 효과 및 상승류 현상이 심한 특징을 가지고 있음으로 이와 같은 유동의 수치해석을 위해 2개 방정식 난류점성 모델 중 RNG k-? 모델을 사용하였으며 유동장의 영향을 가장 많이 받는 배열 회수보일러 최종과열기관의 열전달특성변화를 파악하기위하여 NTU 방식을 이용한 수치해석결과와, 산업계에서 적용하는 설계기법에 의한 결과를 비교하였다. Because of the instability of a flow pattern in the inlet transition square duct (hereinafter referred to as “transition duct”) of a heat recovery steam generator (hereinafter referred to as “HRSG”) in a combined cycle power plant, the Reynolds number in the first row of a tube bank is differs sharply from that in the sectional area of the transition duct. This causes differences in the heat flux in each tube in the tube bank. The computational fluid dynamics (CFD) predictions provide three-dimensional results for velocity, temperature, and other flow parameters over the entire domain of the duct and HRSG. A renormalization group theory (RNG) based k-? turbulent model is used for obtaining the results cited in this study. A porous media option is used for modeling the tube banks and the number of transfer units method is used for determining the heat transfer characteristics. This study describes a comparison between the numerical simulation results and actual design output.