• Korean Journal of Metals and Materials
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• v.49 no.11
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• pp.860-867
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• 2011

This study was performed to investigate the effects of the driving force for reduction and the surfactant (polyacrylic acid) on the size of Ag particles. As the driving force for reduction increases, the size of particles decreases due to a decrease of initial nuclei-size. Also, an increase of pH increases the amount of ionized surfactant, which leads to a decrease of particle size due to the prevention of particle growth. Both the driving force and the surfactant may affect the particle size, but the surfactant appeared to be a more dominant factor than reduction potential in terms of controlling the particle size. An increase of surfactant in the range of pH=3-4 decreases the size of Ag particles, although the reduction potential also decreases.

• Journal of Environmental Health Sciences
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• v.32 no.5 s.92
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• pp.478-484
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• 2006

There was no significant difference in the CADR (Clean Air Delivery Rate) between physical aerosols, NaCl and smoke, and biological aerosols, airborne MS2 virus and P. fluorescens, which implicate that the hybrid-type of air purifier, applying the unipolar ion emission and the radiant catalytic ionization, imposed identical reduction effect on both physical aerosol and bioaerosol. Ventilation decreases the efficiency of air cleaning by unipolar ionization because high ventilation diminishes the particle concentration reduction effect. The particle removal efficiency decreases with increase in the chamber volume because of the augmented ion diffusion and higher ion wall loss rate. Particle size affects the efficiency of air ionization. The efficiency is high for particles with very small diameter because reduction of charge increases with particle size. If there is no increasing supply of ions, the efficiency of air cleaning by unipolar ionization increases with respect to initial concentration of particles because of the large space charge effect at high particle concentration and amplified electric field.

• Advances in nano research
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• v.5 no.4
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• pp.359-372
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• 2017

Metallic copper nanoparticles were synthesised by reduction of copper ions in aqueous solution, and metal-metal bonding by using the nanoparticles was studied. A colloid solution of metallic copper nanoparticles was prepared by mixing an aqueous solution of $CuCl_2$ (0.01 M) and an aqueous solution of hydrazine (reductant) (0.2-1.0 M) in the presence of 0.0005 M of citric acid and 0.005 M of n-hexadecyltrimethylammonium bromide (stabilizers) at reduction temperature of $30-80^{\circ}C$. Copper-particle size varied (in the range of ca. 80-165 nm) with varying hydrazine concentration and reduction temperature. These dependences of particle size are explained by changes in number of metallic-copper-particle nuclei (determined by reduction rate) and changes in collision frequency of particles (based on movement of particles in accordance with temperature). The main component in the nanoparticles is metallic copper, and the metallic-copper particles are polycrystalline. Metallic-copper discs were successfully bonded by annealing at $400^{\circ}C$ and pressure of 1.2 MPa for 5 min in hydrogen gas with the help of the metalli-ccopper particles. Shear strength of the bonded copper discs was then measured. Dependences of shear strength on hydrazine concentration and reduction temperature were explained in terms of progress state of reduction, amount of impurity and particle size. Highest shear strength of 40.0 MPa was recorded for a colloid solution prepared at hydrazine concentration of 0.8 M and reduction temperature of $50^{\circ}C$.

• Transactions of the Korean hydrogen and new energy society
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• v.28 no.5
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• pp.554-560
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• 2017

Reduction reactivity of new oxygen carriers for chemical looping combustion system were investigated using $CH_4$ as a reduction gas in a bubbling fluidized bed reactor and compared with that of former SDN70 oxygen carrier. New oxygen carriers showed good reduction reactivity at different $CH_4$ concentration. N018-R2 particle represented better reactivity than SDN70 at high $CH_4$ concentration. N018-R2 particle showed higher fuel conversion and $CO_2$ selectivity than those of SDN70 particle within the temperature range of $750-900^{\circ}C$. Moreover, attrition loss of N018-R2 particle was almost same with that of SDN70 particle. Consequently, we could select N018-R2 particle as the best oxygen carrier.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.4
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• pp.348-358
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• 2008

Reduction reactivity and carbon deposition characteristics of mass produced oxygen carrier particle(OCN-650) have been investigated by using hydrogen, methane, syngas, and natural gas as fuels. For all fuels, the maximum conversion and oxygen transfer capacity increased as the temperature increase. The reduction rate and the oxygen transfer rate increased as the temperature increase for methane. However, those values showed maximum at 900$^{\circ}C$ for hydrogen, syngas, and natural gas. To explain consistently the change of maximum conversion, reduction rate, oxygen transfer capacity, oxygen transfer rate and degree of carbon deposition for different fuels, new parameters such as reactive carbon contents and require oxygen per input gas were adopted.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2005.05a
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• pp.89-92
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• 2005

This study investigates influence of particle properties of crushed sand on the duality of concrete. The test shows that an increase of fineness modulus(FM) resulted in high slump and air contents, while compressive strength decreased due to decreased adhesion with reduction of surface area. As grain shape become rounder, the slump of concrete increased, due to reduction of internal friction, and increased air contents. The reduction of adhesion by abrasion of surface declined compressive strength during the process of manufacturing crushed sand. Increase of powder contents decreased slump and it also decreased air contents due to the effect of filling air void. In addition. using powder contents increased compressive strength, but could not find any difference of bleeding and tensile strength with particle properties.

• Smart Structures and Systems
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• v.11 no.1
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• pp.69-86
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• 2013

An efficient methodology using static test data and changes in natural frequencies is proposed to identify the damages in structural systems. The methodology consists of two main stages. In the first stage, the Damage Signal Match (DSM) technique is employed to quickly identify the most potentially damaged elements so as to reduce the number of the solution space (solution parameters). In the second stage, a particle swarm optimization (PSO) approach is presented to accurately determine the actual damage extents using the first stage results. One numerical case study by using a planar truss and one experimental case study by using a full-scale steel truss structure are used to verify the proposed hybrid method. The identification results show that the proposed methodology can identify the location and severity of damage with a reasonable level of accuracy, even when practical considerations limit the number of measurements to only a few for a complex structure.

• Nuclear Engineering and Technology
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• v.38 no.8
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• pp.763-778
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• 2006

Injection of microbubbles within the turbulent boundary layer has been investigated for several years as a method to achieve drag reduction. However, the physical mechanism of this phenomenon is not yet fully understood. Experiments in a channel flow for single phase (water) and two phase (water and microbubbles) flows with various void fraction values are studied for a Reynolds number of 5128 based on the half height of the channel and bulk velocity. The state-of-the art Particle Tracking Velocimetry (PTV) measurement technique is used to measure the instantaneous full-field velocity components. Comparisons between turbulent statistical quantities with various values of local void fraction are presented to elucidate the influence of the microbubbles presence within the boundary layer. A decrease in the Reynolds stress distribution and turbulence production is obtained with the increase of microbubble concentration. The results obtained indicate a decorrelation of the streamwise and normal fluctuating velocities when microbubbles are injected within the boundary layer.

• Journal of Sensor Science and Technology
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• v.20 no.5
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• pp.357-362
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• 2011

This paper demonstrates a novel electrodynamic technique to remove particles from the wall of microchannels. Dielectrohporesis(DEP) is generated by applying alternating electric potentials to the interdigitated electrodes integrated at the bottom of the micro-channel. The proposed technique is applied to a general microfluidic channel as a feasibility test. To examine the wall loss reduction efficiency, 10 ${\mu}m$ diameter Polystyrene latexes(PSL) were supplied to the inlet of the device. Then, the concentration of collected particles through devices was measured. In the experiment for 10 ${\mu}m$ diameter PSL particles, the concentration of the injected particles was $174.25{\times}10^4$ particles/ml. However, the concentration of collected particles at the outlet was $52.25{\times}10^4$ particles/ml. Only 30 % of particles had arrived at the outlet and 70 % of particles had adhered to the wall of the microfluidic channel. By applying alternating electric potentials from 0 to 20 $V_{pp}$ at 3 MHz, the concentration of injected particles was 135.00${\times}10^4$ particles/ml, the concentration of collected particles was increased as $105.25{\times}10^4$ particles/ml at 20 $V_{pp}$ at the outlet. When the electric potential was 20 $V_{pp}$, the particle loss was decreased by 39 % (initial loss: 70 %, loss at 20 Vpp: 31 %) with 10 ${\mu}m$ particle. The particle loss was decreased along to the incensement of electric potentials and the enlargement of the diameter of particles. According to these measured results, it was confirmed that the proposal of using DEP technique could be a good candidate for particle loss reduction in micro-particle processing chip application. Moreover, it is expected that the proposed technique could enhance performance of microfluidic and biochip devices.

• 한국연소학회:학술대회논문집
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• 2004.11a
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• pp.117-123
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• 2004

The burning characteristics of interacting coal particles in a convective flow are numerically investigated at various Reynolds numbers. The transient combustion of 2-dimensionally arranged particles, both the fixed particle distances of 5 radii to 20 radii horizontally and 3 radii to 24 radii vertically, is studied. The results obtained from the present numerical analysis reveal that the transient flame configuration and retardation of particle temperature augmentation with the horizontal or vertical particle spacing substantially influence devolatilization process and carbon conversion ratio of interacting particles. Volatile release and carbon conversion ratio of the second particle with decreasing horizontal and vertical particle spacing decrease gradually, whereas those of the first particle with decreasing vertical particle spacing increases due to flow acceleration. When the vertical particle spacing is smaller than $6R_{o}$, volatile release and carbon conversion ratio of the second particle decrease greatly due to reduction of flame penetration depth.