• Korea-Australia Rheology Journal
• /
• v.19 no.3
• /
• pp.99-107
• /
• 2007

A nanofluid is a mixture of solid nanoparticles and a common base fluid. Nanofluids have shown great potential in improving the heat transfer properties of liquids. However, previous studies on the characteristics of nanofluids did not adequately explain the enhancement of heat transfer. This study examined the distribution of particles in a fluid and compared the mechanism for the enhancement of heat transfer in a nanofluid with that in a general microparticle suspension. A theoretical model was formulated with shear-induced particle migration, viscosity-induced particle migration, particle migration by Brownian motion, as well as the inertial migration of particles. The results of the simulation showed that there was no significant particle migration, with no change in particle concentration in the radial direction. A uniform particle concentration is very important in the heat transfer of a nanofluid. As the particle concentration and effective thermal conductivity at the wall region is lower than that of the bulk fluid, due to particle migration to the center of a microfluid, the addition of microparticles in a fluid does not affect the heat transfer properties of that fluid. However, in a nanofluid, particle migration to the center occurs quite slowly, and the particle migration flux is very small. Therefore, the effective thermal conductivity at the wall region increases with increasing addition of nanoparticles. This may be one reason why a nanofluid shows a good convective heat transfer performance.

• Journal of Advanced Marine Engineering and Technology
• /
• v.34 no.4
• /
• pp.508-514
• /
• 2010

The objective of this work presented here was experimental study of steadystate and cold start exhaust nano-sized particle characteristics from common rail diesel engine. The effect of the diesel oxidation catalyst (DOC) on the particle number reduction was insignificant, however, particle number concentration levels were reduced by 3 orders of magnitude into the downstream of diesel particulate filter (DPF). In high speed and load conditions, natural regeneration of trapped particle occurred inside DPF and it was referable to increase particle number concentration. As fuel injection timing was shifted BTDC $6^{\circ}CA$ to ATDC $4^{\circ}CA$, particle number concentration level was slightly reduced, however particle number and size was increased at ATDC $9^{\circ}CA$. Nucleation type particle reduced and accumulation type particle was increased on EGR condition.

• Journal of the Korean Graphic Arts Communication Society
• /
• v.14 no.2
• /
• pp.81-99
• /
• 1996

The characteristics of printing inks are affected, to a greater or lesser extent, by the size and distribution of the pigment particles in the dispersion. Color strength, transparency and gloss increase with a decrease in particle size of pigments and with an increase in surface area of pigments. On the contrary, opacity and lightfastness tend to increases with an increase in particle size of pigments and with a decrease in surface are and particle size if pigments on the physical properties of printing ink which made up vehicles for sheet fed and organic pigment Lake Red C(C.I Pigment Red 53:1) that different surface area and particle size.

• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.31A no.5
• /
• pp.134-148
• /
• 1994

A full two-dimensional MOSFET simulator utilizing the Mixed Particle Monte Carlo method is introduced. Particle simulation for both electrons and holes are self-consistently coupled with Poisson 's equation. To demonstrate the performance of the simulator, steady state and transient state solutions of the terminal characteristics and the internal physical quantities are obtained for 0.25$\mu$m MOSFETs with three different structures` conventional single drain, LDD and GOLD MOSFET structures.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
• /
• 1997.10a
• /
• pp.67-69
• /
• 1997

Abstract - In this paper, the behaviour and effect of various particles made of conducting wires( Fe, Cu, Al ) in a SF6 insulated electrode system, are presented. It is shown that the ac breakdown voltage of compressed SF6 is influenced by different conducting particles. The breakdown voltage due to the particle is dependent of a class of particle. The breakdown voltage due to Cu particle was the highest and the breakdown voltage due to Al particle was the lowest.

• Journal of the Korean Magnetics Society
• /
• v.6 no.1
• /
• pp.21-27
• /
• 1996

The effects of various manufacturing conditions on the characteristics of metal particle tape using ultra-fine metal powder were investigated. As functions of kneading conditions and milling solid contents. coating thickness, orientation, calender and curing conditions. various properties of the tapes were studied. By the consideration of physical and eletromagnetic properties of the tapes, optimum process conditions were determined. As a result of above investigations, we concluded that manufacturing processes were very important factor in addition to dispersion behavior of particles for achieving maximum properties of the metal particle tape.

• Proceedings of the Korean Society of Marine Engineers Conference
• /
• 2005.11a
• /
• pp.21-22
• /
• 2005

A study on the wear characteristics of the white metal(Sn-base alloy) bearing as a function of particle contamination level was conducted in order to establish control criteria of the lubricant in the 2-stroke marine diesel engine. Particle contamination level of the lubricants ranged from NAS 10 to 12 for the experiments. Bar-on-plate type wear test was performed using reciprocating wear tester. Based on this study it was found that there was no noticeable difference in weight loss of the white metal for NAS10 and NAS11(particle contamination level). Surface roughness of the white metal bearing after the wear test of 8hrs for the highly contaminated lubricant(NAS12 level) was up to $6{\mu}m$ in Rmax whilst that of the less contaminated lubricants(NAS10 & 11) was less than $1.5{\mu}m$ in Rmax.

• Journal of Advanced Marine Engineering and Technology
• /
• v.34 no.7
• /
• pp.981-990
• /
• 2010

The main objective of this study is to investigate the fluid flow and the heat transfer characteristics of nanofluids using multi-phase thermal LBM and to realize theenhancement of heat transfer characteristics considered in the Brownian motion. In multi-phase, fluid component($H_2O$) is driven by Boussinesq approximation, and nanoparticles component by the external force gravity and buoyancy. The effect of Brownian motion as a random movement is modified to the internal velocity of nanoparticles(Cu). Simultaneously, the particles of both the phases assume the local equilibrium temperature after each collision. It has been observed that when simulating $H_2O$-Cu nanoparticles, the heat transfer is the highest, at the particle volume fraction 0.5% of the particle diameter 10 nm. The average Nusselt number is increased approximately by 33% at the particle volume fraction 0.5% of the particle diameter 10 nm when compared with pure water.

• Explosives and Blasting
• /
• v.8 no.4
• /
• pp.23-29
• /
• 1990

Some surface blasting vibration was measured to determine site constants and vibration frequency was analyzed. The results are summarized as follows; 1) Design method to predict particle velocities was introduced using the logarithmic normal distribution characteristics of peak particle velocities. 2) Scaled distance diagram to determine limiting charge was presented. 3) Line fitness between particle velocity and scaled distance didn't depend on dominant component of vibration. Prevail fitness was in the order of transverese, peak, vertical and radial component. 4) Dominant component of particle velocity didn't related to drilling direction. Frequency was lowered as distance enlarged. Duration time of vibration was shortened as charge decreased.

• Proceedings of the KIEE Conference
• /
• 1995.11a
• /
• pp.465-468
• /
• 1995

The gas-insulated switchgear(GIS) has made high-reliability, high-safety, compact substations possible by using $SF_6$ gas. They are likely to be further developed toward higher voltages and targer capacities, along with greater compactness and lower cost. Although $SF_6$ gas has excellent insulation performance, breakdown voltages are reduced by the conducting particles. Thus, extensive studies have been made on the breakdown characteristics of $SF_6$ gas in particle contaminated conditions. Experiments were carried out for fired particle and free particle in a coaxial electrode system with DC and AC voltages. This paper represents the experimental results of the processes involved in electrical breakdown in compressed $SF_6$ gas, where breakdown is initiated by conducting particles.