Papers by Author: Kyu Sun Lee

Abstract: Due to the environmental concerns, especially the greenhouse effect and GWP (Global Warming Potential), the carbon dioxide was investigated as an alternative natural refrigerant to replace HFCs (HydroFluoroCarbons) in refrigerator or air conditioning systems. To develop new compressor, especially rotary type, the friction and wear characteristics of sliding surfaces between vane and flange in the rotary compressor were evaluated in this paper. Several hard coatings, such as TiN, CrN and WC/C, were applied on vane surfaces in order to improve the tribological characteristics, and their performances were evaluated experimentally. The vane-on-flange type lubricated sliding tests were performed with a high pressure wear tester using HFC (R410A) and carbon dioxide. From the tests, wear volumes of vane surfaces applied with various coatings were compared each other.

Abstract: In order to protect the global environment, especially on the point of the greenhouse effect, carbon dioxide should be used as a natural refrigerant. Because new compressors with CO2 are going to be operated under the high pressure, the interaction between sliding surfaces in the compressor becomes very important. To develop new compressor, especially rotary type, the friction and wear characteristics of sliding surfaces were very important. In this paper, the surface interactions between a shaft and a flange, which were one of the contacting parts in compressor, were evaluated. The frictional forces and wear amounts in boundary lubricated sliding condition were measured using the pin-on-disk tester. Two types of refrigerants were used, namely R410A and CO2 to compare the tribological characteristics of conventionally used one with new natural refrigerant. It was found that CO2 lead to a bad lubricity as compared with R410A or pure oil due to the formation of relatively thin protective layer on the sliding surface. Smooth surface of shaft produced lower values of friction and wear than rough surfaces. The smooth surfaces represented much more spheroidal graphite, which had very favorable tribological characteristics, on the sliding surfaces.

Abstract: The tribological performance of ordered mesoporous carbons (CMK-3) as lubricant additives is investigated at ambient temperature. The effects of CMK-3 on the frictional forces, wear amounts and cycles to scuffing are measured using a ball-on-disk tester. It was found that there was little difference in the frictional forces and wear amounts of the oils with and without CMK-3. However, the scuffing time of the oil with CMK-3 was much longer than that of the pure mineral oil in sliding tests. CMK-3 were very effective on maintaining the oil gap and protecting the surfaces in boundary lubricated sliding.

Abstract: The tribological performance of multi-walled carbon nanotubes (MWNT) in mineral oils is investigated at ambient temperature. The frictional forces, wear amounts and cycles to scuffing of the oils with nanotubes and without those were measured using the ball-on-disk tester. It was found that there were little differences in the frictional forces and wear amounts of two oils. However, the scuffing times of oils with nanotubes were much longer than those of oils without nanotubes in sliding tests. The nanotubes were very effective on maintaining the oil gap and protecting the surfaces in boundary lubricated sliding.