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Wear and Adhesion Properties of Single-Layer Graphene
박찬형,김주희,안효석 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.19 No.10
Wear and adhesion properties of single-layer graphene deposited on a silicon wafer were investigated in this study. Wear characteristics was studied at nanoscale by using friction force microscopy (FFM) while adhesion property was measured at microscale with a scratch tester. The microscratch test was performed on a single-layer graphene by linearly increasing normal load from 0 to 200 mN. The Kelvin probe force microscopy (KPFM) was used to locally measure surface potential in the tested surface to quantitatively measure the area of damage of graphene layer. The nanoscale wear test results showed two stages of damage of graphene layer; a steady increase at low loads and a relatively rapid increase at high loads. The microscratch test results revealed that severe damage of the layer occurred without introduction of minor damage stage. We demonstrated that the KPFM was highly effective in quantifying the damage of graphene layer.
응축전열관 외부형상 변화에 따른 HFC134a의 열전달 실험
박찬형,이영수,정진희,강용태 대한설비공학회 2006 설비공학 논문집 Vol.18 No.8
The objectives of this paper are to study the characteristics of heat transfer for enhanced tubes(19.05mm) used in the condenser with high saturation temperatures and to provide a guideline for optimum design of a condenser using HFC134a. Three different enhanced tubes are tested at a high saturation temperature of 59.8℃(16bar); a low-fin and three turbo-C tubes.. The refrigerant, HFC134a is condensed on the outside of the tube while the cooling water flows inside the tube. The film Reynolds number varies from 130 to 330. The wall subcooling temperature ranges from 2.7℃ to 9.7℃. This study provides experimental heat transfer coefficients for condensation on the enhanced tubes. It is found that the turbo- C(2) tube provides the highest heat transfer coefficient.