• Nuclear Engineering and Technology
• /
• v.55 no.7
• /
• pp.2534-2546
• /
• 2023

Gas-cooled space reactor, which adopts He-Xe gas mixture as working fluid, is a better choice for megawatt power generation. In this paper, thermal-hydraulic characteristics of He-Xe gas mixture in 2×2 rod bundle wrapped with helical wires is numerically investigated. The velocity, pressure and temperature distribution of the coolant are obtained and analyzed. The results show that the existence of helical wires forms the vortexes and changes the velocity and temperature distribution. Hot spots are found at the contact corners between helical wires and fuel rods. The highest temperature of the hot spots reach 1600K, while the mainstream temperature is less than 400K. The helical wire structure increases the friction pressure drop by 20%-50%. The effect extent varies with the pitch and the number of helical wires. The helical wire structure leads to the reduction of Nusselt number. Comparing thermal-hydraulic performance ratios (THPR) of different structures, the THPR values are all less than 1. It means that gas-cooled space reactor adopting helical wires could not strengthen the core heat removal performance. This work provides the thermal-hydraulic design basis for He-Xe gas cooled space nuclear reactor.

• Proceedings of the KSR Conference
• /
• 2011.05a
• /
• pp.1189-1194
• /
• 2011

The Maglev train is operated by levitating from a power of a large number of magnets and moving without direct contact to railway track so that reduces noise and vibration due to mechanical friction. Also, the Maglev passes sharp curves and steep hill without any difficulties. The Maglev has a potential to be an alternative transport system urban areas. For successful commercializing of Maglev, the organization of interface for safety and reliability of third rail system are one of the key considerations. Especially, the components of the third rail system, such as power rail, expansion joints, FRP section insulator, and supporter with epoxy insulator, should be durable, convenient for construction, and easy to maintenance. This paper analyzes the characteristics of the third rail system components and proposes organization of interface for system engineering. The operating tests of KIMM for the proposed third rail system verify the safety. Also, this paper analyzes the life cycle of the system components to improve the system reliability and evaluation.

• Journal of the Korean Society for Precision Engineering
• /
• v.28 no.7
• /
• pp.777-782
• /
• 2011

Micro features on the surface are well-known to have significant effects on optical or mechanical properties such as the optical interference, reflectance at the surface, contact angle, interfacial friction, etc. These surface micro features are increasingly employed to enhance the functionality of the applications in various application areas such as optical components for LCD or solar panel. Diverse surface features have been proposed and some of them are showing excellent efficiency or functionality, especially in optical applications. Most applications employing the micro features need manufacturing process for mass production and the injection molding and roll-to-roll forming, which are typical processes for mass production adopting polymeric materials, may be also preferred for micro patterned plastic product. Since the functionality or efficiency of the surface structures generally depends on the shape and the size of the structure itself or the array of the structures on the surface, it would be very important to replicate the features very precisely as being designed during the molding the micro pattern applications. In this paper, a series of research activities is introduced for roll-to-roll forming of micro patterned film including filling of patterns with UV curable resin, demolding of surface structures from the roll tool, control of surface energy and cure shrinkage of resin and dispose time and intensity of the UV light for curing of UV curable resin.

• Journal of Powder Materials
• /
• v.22 no.5
• /
• pp.321-325
• /
• 2015

The triboelectric property of a material is important to improve an efficiency of triboelectric generator (TEG) in energy harvesting from an ambient energy. In this study, we have studied the TEG property of a semiconducting $SnO_2$ which has yet to be explored so far. As a counter triboelectric material, PET and glass are used. Vertical contact mode is utilized to evaluate the TEG efficiency. $SnO_2$ thin film is deposited by atomic layer deposition on bare Si wafer for various thicknesses from 5.2 nm to 34.6 nm, where the TEG output is increased from 13.9V to 73.5V. Triboelectric series are determined by comparing the polarity of output voltage of 2 samples among $SnO_2$, PET, and glass. In conclusion, $SnO_2$, as an intrinsic n-type material, has the most strong tendency to be positive side to lose the electron and PET has the most strong tendency to be negative side to get the electron, and glass to be between them. Therefore, the $SnO_2$-PET combination shows the highest TEG efficiency.

• Journal of the Korean Institute of Gas
• /
• v.19 no.1
• /
• pp.6-11
• /
• 2015

This paper is to study the examples for rubber damage and weaken reliability of timing belt, constant velocity joint boot and weather strip in vehicle. The first example, when the service man replaced the new timing-belt of rubber material, he assembled the belt that was weaken it's contact surface because of material transform. He knew the abnormally tearing failure by friction action between belt and sprocket. The second example, it certified the fact that the grease is leaked out boot protecting of constant velocity joint by split of rubber surface because of durability badness. The third example, the weather stripe took the minutely tearing because of damage produced the material transform by crack of chemistry change. It certified the production phenomenon of a tiny noise by coming with outside air because of overlapped the rubber of weather stripe when driving after closing the door. Therefore, the driver must always manage the rubber system part of vehicle.

• Journal of Mechanical Science and Technology
• /
• v.18 no.5
• /
• pp.770-779
• /
• 2004

This paper describes the micro cutting of wear resistant tungsten carbides using PCD (Poly-Crystalline Diamond) cutting tools in performance with SEM (Scanning Electron Microscope) direct observation method. Turning experiments were also carried out on this alloy (V50) using a PCD cutting tool. One of the purposes of this study is to describe clearly the cutting mechanism of tungsten carbides and the behavior of WC particles in the deformation zone in orthogonal micro cutting. Other purposes are to achieve a systematic understanding of machining characteristics and the effects of machining parameters on cutting force, machined surface and tool wear rates by the outer turning of this alloy carried out using the PCD cutting tool during these various cutting conditions. A summary of the results are as follows: (1) From the SEM direct observation in cutting the tungsten carbide, WC particles are broken and come into contact with the tool edge directly. This causes tool wear in which portions scrape the tool in a strong manner. (2) There are two chip formation types. One is where the shear angle is comparatively small and the crack of the shear plane becomes wide. The other is a type where the shear angle is above 45 degrees and the crack of the shear plane does not widen. These differences are caused by the stress condition which gives rise to the friction at the shear plane. (3) The thrust cutting forces tend to increase more rapidly than the principal forces, as the depth of cut and the cutting speed are increased preferably in the orthogonal micro cutting. (4) The tool wear on the flank face was larger than that on the rake face in the orthogonal micro cutting. (5) Three components of cutting force in the conventional turning experiments were different in balance from ordinary cutting such as the cutting of steel or cast iron. Those expressed a large value of thrust force, principal force, and feed force. (6) From the viewpoint of high efficient cutting found within this research, a proper cutting speed was 15 m/min and a proper feed rate was 0.1 mm/rev. In this case, it was found that the tool life of a PCD tool was limited to a distance of approximately 230 m. (7) When the depth of cut was 0.1 mm, there was no influence of the feed rate on the feed force. The feed force tended to decrease, as the cutting distance was long, because the tool was worn and the tool edge retreated. (8) The main tool wear of a PCD tool in this research was due to the flank wear within the maximum value of $V_{max}$ being about 260 $\mu\textrm{m}$.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.11
• /
• pp.1349-1354
• /
• 2013

Sealing structure to prevent flowing hot gas into the driving device, located between the driving shaft and the liner of On-Off valve for controlling the hot gas flow path was studied. Wear occurs due to the constant movement of the driving shaft controlled by actuator on graphite as the sealing material. In this paper, the dynamic wear behavior in high temperature of graphite(HK-6) to be used as sealing material was evaluated. Reciprocating wear test was carried out for the graphite(HK-6) to the relative motion between shaft materials(W-25Re). The results of friction coefficient and specific wear rate according to contact load, sliding speed at room temperature and $485^{\circ}C$ considering the actual operating environment were evaluated. Through the SEM analysis of the worn surface, third body as lubricant films were observed and lubricant effect of third body was considered.

• Korean Journal of Materials Research
• /
• v.5 no.8
• /
• pp.953-959
• /
• 1995

It was investigated that reinforced species, billet condition and extrusion variation in Al 6061 composite material effected on extrusion process of particulate reinforced composite material. The strength of composite material with reinforcement species revealed SiC$\sub$w/> A1$_2$O$\sub$3f/ > A1$_2$O$\sub$3f/ > A1$_2$O$\sub$3f/ orderly. K$\sub$w/ increased as volute fraction increased in all composite material. The composite materials reinforced by A1$_2$ $O_3$required the larger pressure in hot extrusion process than those by SiC$\sub$p/ at all condition. Extrusion process tended to decrease as the semi-angle of extrusion dies increased because larger contact area caused larger shear friction. Extrusion temperature went up about 50$^{\circ}C$ in low elevated deformation temperature. In extrusion temperature above 500$^{\circ}C$, severe tearing occurred on extrusion surface. More reinforcement in volume fraction, more hot tearing.

• Elastomers and Composites
• /
• v.39 no.1
• /
• pp.12-22
• /
• 2004

The plasma surface modification of natural rubber vulcanizate was carried out using chlorodifluoromethane in a radio-frequency (13.56 MHz) electrodeless bell type plasma reactor. The modification was qualitatively assessed by Fourier transform infrared spectroscopy. The frictional force of the plasma-treated surface was found to decrease with the time of plasma treatment. An increase in the surface polarity, as evidenced by the decrease in contact angle of a sessile drop of water and ethylene glycol on the natural rubber vulcanizate surface, was noted with the plasma modification. In the case of similar plasma treatment of glass surface, only a reduction in the polarity was observed. The use of geometric and harmonic mean methods was found to be useful to evaluate the London dispersive and specific components of surface free energy. Irrespective of the method used for evaluation, an increasing trend in the surface free energy was noted with increasing plasma treatment time. However, the harmonic mean method yielded comparatively higher values of surface free energy than the geometric mean method. The plasma surface modification was found to vary the frictional coefficient by influencing the interfacial, hysteresis and viscous components of friction in opposing dual manners.

• Journal of the Korean Geotechnical Society
• /
• v.40 no.1
• /
• pp.5-14
• /
• 2024

PHC piles demonstrate superior resistance to compression and bending moments, and their factory-based production enhances quality assurance and management processes. Despite these advantages that have resulted in widespread use in civil engineering and construction projects, the design process frequently relies on empirical formulas or N-values to estimate the soil-pile friction, which is crucial for bearing capacity, and this reliance underscores a significant lack of experimental validation. In addition, environmental factors, e.g., the pH levels in groundwater and the effects of seawater, are commonly not considered. Thus, this study investigates the influence of vibrating machine foundations on PHC pile models in consideration of the effects of varying pH conditions. Concrete model piles were subjected to a one-month conditioning period in different pH environments (acidic, neutral, and alkaline) and under the influence of seawater. Subsequent repeated direct shear tests were performed on the pile-soil interface, and the disturbed state concept was employed to derive parameters that effectively quantify the dynamic behavior of this interface. The results revealed a descending order of shear stress in neutral, acidic, and alkaline conditions, with the pH-influenced samples exhibiting a more pronounced reduction in shear stress than those affected by seawater.