• 대한기계학회논문집B
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• 제39권1호
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• pp.29-36
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• 2015

나노유체 개발 초기단계에서 기본유체 대비 제조한 나노유체의 열전도율이 얼마나 상승했는지 그 값을 정확히 비교하는 것이 중요하다. 지금까지는 기본유체와 나노유체의 열전도율을 비정상열선법으로 별도 측정한 후 수치적으로 나누어 비교하는 단순한 방법을 사용하였다. 이 때 두 유체의 열전도율 측정이 동시에 이루어지지 않고 절대측정방법의 특성상 측정시스템의 관련 수치들이 정확히 사용되지 않으면 개별 열전도율에 나타나는 오차를 피할 수 없다. 본 연구에서는 비교대상인 두 유체를 동시에 사용하여 열전도율 비를 상대적으로 측정하는 새로운 방법을 제시하였다. 기존 비정상열선법 회로를 변형한 측정회로와 데이터 처리과정을 자세히 설명하였고 엔진오일과 글리세린을 이용한 검증실험을 통하여 제시된 방법의 타당성을 검토하였다.

• Tribology and Lubricants
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• 제34권5호
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• pp.197-207
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• 2018

Thermal deterioration of fuel due to long-term storage influences engine performance and causes malfunctions. Fuel stability is usually evaluated via heat resistance and thermal stability during a brief heat shock at high temperature; storage stability in this scenario means that there is very little change in the quality of the fuel during long-term storage. In addition, rubber-based products such as oil seals, O-rings, and rubber hoses can influence the quality of the fuel. When these rubber products are in contact with fuel, they can swell, mechanically weaken, and occasionally crack, thus leaking low molar weight rubber and additives including plasticizer and antioxidant into the fuel to degrade its properties and shorten its useful lifetime. This study determines the thermal stabilities of three kinds of synthetic fuels by evaluating their low temperature kinematic viscosities, chemical composition changes via GC analyses, gross heat of combustion, and color changes. We evaluate the compression set of O-rings by immersing one NBR and two FKM rubber O-rings in the three synthetic fuel samples in airtight containers at variable storage temperatures for six months; from this, we estimate the lifetimes of the O-rings using the Power law model. There were very little changes in the chemical compositions and gross heat of combustion after six months of the experiment. The lifetimes are thus dependent on the materials of the rubber products, and in particular, the FKM O-ring was calculated to have a theoretical lifetime of 200 to 5,700 years. These results indicate that the synthetic fuels maintain their physical properties even after long-term storage at high temperatures, and the FKM O-ring is suitable for long-term sealing of these fuels.