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수력직경이 작은 평판관내 R-22 및 R-410A 응축에 관한 연구
정호종(Ho-Jong Jeong),민창근(Chang-Keun Min),김내현(Nae-Hyun Kim),윤백(Baek Youn),김만희(Man-Hoe Kim) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.5
In this study, condensation heat transfer tests were conducted in flat aluminum multi-channel tubes using<br/> R-410A, and the results are compared with those of R-22. Two internal geometries were tested; one with a<br/> smooth inner surface and the other with micro-fins. Data are presented for the following range of variables;<br/> vapor quality (0.1 ~ 0.9), mass flux (200 ~ 600 kg/㎡s ) and heat flux (5 ~ 15 kW/㎡). Results show that the<br/> effect of surface tension drainage on the fin surface is more pronounced for R-22 than R-410A. The smaller<br/> Weber number for R-22 may be responsible. For the smooth tube, the heat transfer coefficient of R-410A is<br/> slightly larger than that of R-22. For the micro-fin tube, however, the reverse is true. Possible reasoning is<br/> provided considering the physical properties of the refrigerants.
정호종(Ho-jong Jeong),김정오(Jung-Oh Kim),김내현(Nae-Hyun Kim) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.9
Pressure drop experiments were conducted in flat extruded aluminum tubes -one with smooth inn and the other with micro-finned inner surface- using R-410A. For both tubes, the pressure drop the mass flux or the quality increased. The pressure drop also increased as saturation tempera The Friction data are well correlated by the Martinelli parameter with C=1.
김내현,정호종,조진표,최국광,Kim, Nae-Hyeon,Jeong, Ho-Jong,Jo, Jin-Pyo,Choe, Guk-Gwang 대한기계학회 2001 大韓機械學會論文集B Vol.25 No.12
In this study, convective boiling tests were conducted for enhanced tube bundles. The surface geometry consists of pores and connecting gaps. Tubes with three different pore sizes (d$_{p}$ = 0.20, 0.23 and 0.27 mm) were tested using R-123 and R-l34a for the following range: 8 kg/m$^2$s G 26 kg/m$^2$s, 10 kW/m$^2$ q0 40 kW/m$^2$and 0.1 $\chi$ 0.9. The convective boiling heat transfer coefficients were strongly dependent on heat flux with negligible dependency on mass flux or quality. For the present enhanced geometry (pores and gaps), the convective effect was apparent. The gaps of the present tubes may have served routes for the passage of two-phase mixtures, and enhanced the boiling heat transfer. The convective effect was more pronounced at a higher saturation temperature. More bubbles will be generated at a higher saturation temperature, which will lead to enhanced convective contribution. The pore size where the maximum heat transfer coefficient was obtained was larger for R-l34a (d$_{p}$ = 0.27 mm) compared with that for R-123 (d$_{p}$ = 0.23 mm). This trend was consistent with the previous pool boiling results. For the enhanced tube bundles, the convective effect was more pronounced for R-134a than for R-123. This trend was reversed for the smooth tube bundle. Possible reasoning is provided based on the bubble behavior on the tube wall. Both the modified Chen and the asymptotic model predicted the present data reasonably well. The RMSEs were 14.3% for the modified Chen model and 12.7% for the asymptotic model.model.
HEMA와 CA 및 PVA공중합체의 막제조와 물성에 관한 연구
崔乘載,鄭皓鍾,鄭在均 단국대학교 1993 論文集 Vol.27 No.-
The grafting of 2-hydroxyethyl methacrylate(HEMA) and cellulose acetate(CA) and synthesis polymer poly(vinylalcohol) as a biocompatible material for medical application was investigated in the various condition. The structure of graft copolymer was indentified by using infrared spectroscopy.(IR) The membrane of sytnesis copolymer CA-g-p(HEMA) and PVA-g-p(HEMA) were prepared for a skin substitute and water content, tensile strength, elongation, water vapor transimmision rate(WVTR) and biodegradation the membranes was determind. And the surface structure of graft copolymer membrane characterized by SEM. The water content was about 100% and then tensile strength was 166∼661kg/㎠, 210∼88kg/㎠ at dry condition, 60∼328kg/㎠, 54∼23kg/㎠ at wet condition in the PVA-g-p(HEMA) and CA-g-p(HEMA) membrane respectively. Water vapor transimmision rate(WVTR) was 123.59∼128.54kg/㎠/day like that of the normal skin. From the result of the biodegradation by protein hydrolysis pepsin the biodegradation rate was that at the 4∼5day and accessed to the equilibrium state. From the results obtained in this study, syntheis membrane was found to satisfy most of the basic properties of a skin substitute.