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물결형 슬릿핀이 장착된 핀-관 열교환기의 습표면 성능 실험
김내현,김정식,조진표,윤재호,백종현,이순구,남승백,권형진,Kim, N.H.,Kim, J.S.,Cho, J.P.,Yun, J.H.,Peck, J.H.,Lee, S.G.,Nam, S.B.,Kwon, H.J. 대한설비공학회 1997 설비공학 논문집 Vol.9 No.2
In this study, the wet surface heat transfer coefficients and friction factors of the heat exchanger with slit-wavy fin were measured. Four sample cores of two or three row with fins of 12 fpi or 16 fpi were tested. Tests were conducted in a closed loop wind tunnel, where the heat exchanger was mounted at 45 degree inclination angle. The wet surface heat transfer coefficient was reduced following the procedure given in ARI 420-81. During the course, new definitions of the $\varepsilon$-NTU applicable to enthalpy driving system were introduced. The wet surface heat transfer coefficients were approximately equal to the dry surface values. However, the friction factors were approximately 120% to 170% higher than those of the dry surface. Both the heat transfer coefficient and the friction factor of the wet surface increased as the relative humidity increased, fin pitch decreased, and the number of row decreased, although the difference was not large.
낮은 핀관 (low-fin tube)의 응축 열전달 성능에 관한 실험적 연구
김내현,정인권,김경훈,Kim, N.H.,Jung, I.K.,Kim, K.H. 대한설비공학회 1995 설비공학 논문집 Vol.7 No.2
Low-fin tubes are widely used to enhance condensation heat transfer. In this study, condensation heat transfer experiment was conducted on the low-fin tube using R-11. Three different fin densities-787 fpm (fins per meter), 1102 fpm. 1378 fpm-were tested. The results show that low-fin tube enhances the condensation heat transfer considerablely. The enhancement increases as the fin density increases. It was also found that the fin shape and height have a significant effect on the condensation heat transfer coefficient. Slender or high fins showed a higher condensing heat transfer coefficient compared with fat, low fins. For the tube with 1378 fpm, however, excessive fin height decreased the condensing heat transfer coefficient. The reason may be attributed to the increasing condensate retention angle as the fin density increases. The experimental data are compared with existing prediction models. Results show that Webb's surface tension model predicted the data best (within ${\pm}20%$), which confirms that surface tension plays the major role in low-fin tube condensation.
열전달 촉진관내의 화울링 해석-2차원 리브붙이관에 Kern-Seaton 화울링 모델 적용
김내현,Kim, N.H. 대한설비공학회 1992 설비공학 논문집 Vol.4 No.4
Fouling is "a major unsolved" area in heat transfer research. Currently, fouling researches are performed in every directions-fundamental aspects, modeling and cumulating experimental data. In this study, an attempt was made to extend the knowledge in enhanced tube fouling. The Kern-Seaton fouling model which was originally proposed for smooth tube fouling was extended to repeated rib tubes. Key parameters-mass transfer coefficient and wall shear stress-were modeled for repeated rib tubes. Some critical points related with the enhanced tube fouling-uncertainties in the mass transfer rate, wall shear stress modeling, deformation of roughness shape during fouling-were discussed, and some quantitative evaluations were made.
삼차원 조도관의 압력손실 및 열전달 성능에 대한 실험적 연구
김내현,Kim, N.H. 대한설비공학회 1995 설비공학 논문집 Vol.7 No.2
In this study, pressure drop and heat transfer coefficients were measured in tubes with three dimensional roughness. Dimples were made by rotating the saw-tooth shaped finning disc on the outer tube surface. Resultant dimple shape was oval. Friction and heat transfer tests were performed with a range of roughness variables-roughness height 'e', axial roughness pitch 'p', circumferential roughness pitch 'z'. Within the test range, tube with e=0.5mm, z=5mm, p=3mm performed best. The efficiency ratio(rati of the heat transfer improvement and the pressure drop increase) of the tube approached 1.0 at low Reynolds number, and it was higher than that of the two-dimensional roughess tube of the same roughness height. Test data were predicted by 'discrete element method'. Results show that discrete element method underpredicts the friction data by 2% to 32%, and overpredicts the heat transfer data by-12% to 113%.
김내현(N.H. Kim),김정식(J.S.Kim),조진표(J.P.Cho),윤재호(J.H. Youn),백종현(J.H. Baek),이순구(S.G. Lee),남승백(S.B. Nam),권형진(H.J. Kwon) 대한설비공학회 1996 대한설비공학회 학술발표대회논문집 Vol.1996 No.11
본 연구에서는 물결형 슬릿핀이 장착된 핀-관 열교환기의 습표면 열전달계수와 마찰계수가 측정되었다. 열교환기 샘플은 12 fpi와 16 fpi의 2열과 3열, 모두 네 종류로 구성되었다. 시험은 순환형 풍동에서 수행되었고 열교환기는 시험부 내에 45도로 기울게 장착되었다. 습표면 열전달계수는 ARI 410-81에 제시된 절차에 따라 구해졌는데 그 과정 중 엔탈피 구동 씨스템에 적용가능한 ε-NTU의 정의가 새롭게 도입되었다. 습표면 열전달계수는 건표면의 값과 유사하였고 마찰계수는 건표면보다 120% - 170% 증가하였다. 습표면 열전달계수와 마찰계수 모두 큰 차이나지는 않지만 상대습도가 증가할수록, 핀핏치가 감소할수록 그리고 열수가 감소할수록 증가하였다.