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수평미세관의 직경이 R-22 및 R-407C 비등열전달에 미치는 영향
윤국영,최광일,오종택,Yoon, Kuk-Young,Choi, Kwang-Il,Oh, Jong-Taek 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.2
Boiling heat transfer coefficients and pressure drops for R-22 and R-407C were measured in horizontal micro-channels. The test section is stainless steel tube, inner tube diameters are 1.8mm and 2.8mm, and the respective lengths are 1500mm and 3000mm. The range of mass flux is 300-600kg/$m^2$s and heat flux is 5-15kW/$m^2$. In this results, pressure drop increased linearly for both R-22 and R-407C with increased mass flux, but the increase of heat flux did not affect the pressure. In addition, the pressure drop was fairly increased in the high quality region rather than low quality region. In the range of low quality, the mass flux had a small affect on the heat transfer coefficients, however, in high quality region, the heat transfer coefficients increased even more with increasing mass flux. Under the low quality region and low mass flux, the heat transfer coefficients increased with increasing heat flux densities. The effects of inner tube diameter were clearly observed. Namely, the measured pressure drop inside inner tube diameter 1.8 mm is higher than 2.8 mm with increasing the mass flux and heat flux. Also, the measured local heat transfer coefficient inside inner tube diameter 1.8 mm is higher than 2.8 mm in the range of high qualities. The experimental data for R-407C compared with proposed correlation using pure refrigerant. The experimental data for R-407C was more decreased than the proposed correlation for pure refrigerant up to 50% or more.
윤진호,조국영,성시준 한국고분자학회 2012 Macromolecular Research Vol.20 No.5
Patterning and aligning are the most distinctive research areas in surface science. In this paper, we demonstrate a fabrication method for the simultaneous formation of a wall-structured surface relief and a molecular aligning region between the walls. A photoreactive polymer, poly(vinyl cinnamate) (PVCi), was used as the matrix;it was coated either onto a rigid glass substrate or a flexible plastic substrate. We used a solvent-assisted micro-molding poly(dimethylsiloxane) stamp to form 10-μm-wide and 10-μm-high walls every 100 μm on the matrix. The direction of the molecular alignment in the region between the walls was perpendicular to the direction of the walls;this finding was confirmed by the subsequent liquid crystal (LC) alignment investigation. The alignment of this wide region between the wall structures is uncommon and differs from the molecular alignment induced by the microgroove topology due to the patterning. Additionally, the application of linearly polarized ultraviolet irradiation onto the photoreactive PVCi improved the molecular alignment either on the region between the walls or on the lateral side of the walls; this finding was confirmed by polarized light microscopy imaging. The simultaneous formation of the wall support in the molecular aligning region can be used in flexible LC displays, in which the maintenance of cell gaps and the aligning of the LC material play a critical role in display performance.