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정길완,이관수,김우승,Chung, Kilyoan,Lee, Kwan-Soo,Kim, Woo-Seung 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.8
In this study, the general thermal and flow characteristics of flat tube with micro-channels has been studied and the correlation of Nusselt number and friction factor is proposed. The optimal flat tube geometry is determined by optimal design process. It is assumed to be a three dimensional laminar flow in the analysis of thermal and flow characteristics. The periodic boundary condition is applied since the geometry of flat tube with micro-channels shows uniform cross-section in primary flow direction. Local Nusselt number is examined for thermal characteristics of each membrane, and module average Nusselt number and friction factor are calculated to determine the characteristics of the heat transfer and pressure drop in overall flat tube with microchannels. The correlations between Nusselt number and friction factor are given by Reynolds number, aspect ratio of membranes, and the width of flat tube. ALM (Augmented Lagrangian Multiplier) method is applied to the correlations to determine an optimal shape of flat tube. It is shown that the optimal aspect ratio of flat tube is approximately 1.0, irrespective of the width of flat tube and Reynolds number.
다공성 모델링을 이용한 평행류 열교환기의 열.유동 해석
정길완,이관수,Jeong, Gil-Wan,Lee, Gwan-Su 대한기계학회 2001 大韓機械學會論文集B Vol.25 No.12
Numerical analysis on a parallel flow heat exchanger(PFHE) is performed using 2 dimensional turbulent porous modeling. This modeling can consider three-dimensional configuration of passage (flat tube with micro-channels), and the stability and accuracy of numerical results are improved. The geometrical parameters(e.g., the position of separators, inlet/outlet, and porosity of passages of a PFHE) are varied in order to examine the flow and thermal characteristics and flow distribution of the single phase multiple passages system. The flow non-uniformities along the paths of the PFHE are observed to evaluate the thermal performance of the heat exchanger. The location of inlet affects the heat transfer, and the location of outlet affects the pressure drop. The porosity with the optimum thermal performance is around 0.53.
정길완,이관수,Chung, Kil-Yoan,Lee, Kwan-Soo 대한기계학회 2002 大韓機械學會論文集B Vol.26 No.6
The modeling for turbulent flow through a porous media has not been confirmed because of a undetermined constant which appears in the governing equations. In present study, the turbulent porous modeling based on the local thermal equilibrium has been extended to the turbulent clear flow. A undetermined constant is also suggested by microscopic analysis. The microscopic analysis is performed in the flat tube with micro-channels, and it confirms that the undetermined constant is 0.99. It is shown that the results of the macroscopic analysis using confirmed constant agree well with those of the microscopic analysis with a maximum error of 3.5%.
평행류 열교환기의 열.유동 특성에 대한 설계인자의 최적화
정길완,이관수,Chung, Kil-Yoan,Lee, Kwan-Soo 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.5
For the heat and fluid flow analyses of a parallel flow heat exchanger, an improved model considering the effect of flat tube with micro-channels is proposed. The effect of flow distribution on the thermal performance of a heat exchanger is numerically investigated. The flow distribution is examined by varying geometrical parameters, i.e., the position of the separators and the inlet/outlet, and the aspect ratio of micro-channels of the heat exchanger. The flow nonuniformities along the paths of the heat exchanger are proposed and observed to evaluate the thermal performance of the heat exchanger. The optimization using ALM method has been accomplished by minimizing the flow nonuniformity. It is found that the heat transfer rate of the optimized model is increased by 6.0% of that of the reference heat exchanger model, and the pressure drop by 0.4%
정길완(Kilyoan Chung),이관수(Kwan-Soo Lee) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.5
In this study, the turbulent porous modeling based on the local thermal equilibrium has been<br/> extended to the turbulent clear flow. For the analysis of tube geometry, the undetermined constant is<br/> also suggested by microscopic analysis. The microscopic analysis is performed in the flat tube with<br/> micro-channels, and it confirms that the undetermined constant is 0.99. It is shown that the results of<br/> the macroscopic analysis using confirmed constant agree well with those of the microscopic analysis<br/> with a maximum error of 3.5%.
오석진,정길완,이관수,Oh, Seok-Jin,Chung, Kil-Yoan,Lee, Kwan-Soo 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.6
In the present study, the heat and flow characteristics of a parallel-flow heat exchanger are numerically analyzed by using three-dimensional turbulent modeling. Heat transfer rate and pressure drop are evaluated using the concept of the efficiency index by varying the locations, the shapes and angles of inlet/outlet, and the protrusion height of flat tube. It is found that negative angle of the inlet improves the heat transfer rate and pressure drop. Results show that the locations of the inlet and outlet should be toward the right side and the left side to the reference model, respectively, in order to enhance the heat transfer rate and pressure drop. Increasing the height of the lower header causes pressure drop to decrease and yields the good flow characteristics. The lower protrusion height of flat tube shows the improvement of the heat transfer rate and pressure drop. The heat transfer rate is greatly affected by the parameters of outlet side such as the location and angle of the outlet. However, the pressure drop is influenced by the parameters of inlet side such as the location and angle of inlet and the height of the header.
직교하는 단락형 리브를 부착한 판형 열교환기 관내측 열유동 해석
이관수,문형규,정길완,Lee, Kwan-Soo,Moon, Hyoung-Kyu,Chung, Kilyoan 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.5
The purpose of this work is to Investigate the pressure drop and the heat transfer characteristics in the channel of plate heat exchanger with crossed-discrete ribs. The flow is assumed to be three-dimensional, laminar and periodically fully developed. Computations have been carried out for angles of attack from $0^{\circ}$ to $90^{\circ}$ and ratios of rib height from 0.15 to 0.46 for various values of Reynolds and Prandtl numbers. The heat transfer was improved by inclined ribs generating helical vortices and secondary flows. The results show that the pressure drop has a maximum value at $70^{\circ}$ and the heat transfer has a maximum value at $45^{\circ}$. As the rib height increases, the pressure drop and the heat transfer increase quadratically, and the increasing rate of pressure drop is higher than that of the heat transfer. As Reynolds number increases, the pressure drop increases in proportion to the square of Reynolds number and the heat transfer increases linearly.