• Journal of ILASS-Korea
• /
• v.18 no.3
• /
• pp.126-131
• /
• 2013

This paper describes the effect of ultrasonic frequency(f) on the atomization and deformation characteristics of single water droplet in an acoustic levitation field. To achieve this, the ultrasonic levitator that can control sound pressure and velocity amplitude by changing frequency was installed, and visualization of single water droplet was conducted with high resolution ICCD and CCD camera. At the same time, atomization and deformation characteristics of single water droplet was studied in terms of normalized droplet diameter($d/d_0$), droplet diameter(d) variation and droplet volume(V) variation under different ultrasonic frequency(f) conditions. It was revealed that increase of ultrasonic frequency reduces the droplet diameter. Therefore, it is able to levitate with low sound pressure level. It also induces the wide oscillation range, large diameter and volume variation of water droplet. In conclusion, the increase of ultrasonic frequency(f) can enhance the atomization performance of single water droplet.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.2 s.233
• /
• pp.180-188
• /
• 2005

It is well known that a lean burn engine caused by stratified mixture formation has many kinds of advantages to combustion characteristics, such as higher thermal efficiency and lower CO, NOx levels than conventional homogeneous mixture combustion. Although this combustion can achieve low fuel consumption technology, it produces much unburned hydrocarbon and soot because of heterogeneous equivalence ratio in the combustion chamber. Therefore, the stratified mixture formation technology is very important to obtain the stable lean combustion. In this paper, fundamental studies for stratified combustion were carried out using a constant volume combustion chamber. The local effect of mixture formation according to control air-fuel distribution in the chamber was examined experimentally. In addition, the effect of turbulence on stratified charge combustion process was observed by schlieren photography. From this study, we found that the flame propagation speed increase with swirl flow and the swirl promotes the formation of fuel and air mixture.

• Journal of Power System Engineering
• /
• v.20 no.3
• /
• pp.11-16
• /
• 2016

The effect of carbides on the tensile properties in 0.5C-17Cr-0.5Ni martensitic stainless steel was studied. With the increase of austenitizing temperature, the volume fraction of residual carbide was decreased rapidly. In tempered specimens after quenching, the volume fraction of total carbide was decreased with the increase of austenitizing temperature. In tempered specimens after quenching, strength was decrease and elongation was increased with the increase of austenitizing temperature. Tensile strength was increase and elongation was decreased with the increase of volume fraction of residual and total carbides. With the increase of austenitizing temperature, the tensile properties of mod. 0.5C-17Cr-0.5Ni martensitic stainless was affected greatly by residual carbide than tempered carbide.

• Journal of Ocean Engineering and Technology
• /
• v.22 no.6
• /
• pp.35-40
• /
• 2008

The effect of counterpart roughness on abrasive wear characteristics of side plate materials of FRP ship, which were composed of glass fiber and unsaturated polyester resin composites, were investigated at ambient temperature by pin-an-disc friction test. The friction coefficient, wear rate and cumulative wear volume of these materials against SiC abrasive paper were determined experimentally. The wear rate of these materials decreased rapidly with sliding distance and then maintained a constant value. It was increased as counterpart roughness was rougher in a wear test. The cumulative wear volume tended to increase nonlinearly with sliding distance and depended on applied load and sliding speed for these composites. It could be verified by SEM photograph of fracture surface that major failure mechanisms were overlapping layers, microcutting, deformation of resin, delamination, and cracking.

• Journal of ILASS-Korea
• /
• v.14 no.2
• /
• pp.59-64
• /
• 2009

These experiments are close examination of spray characteristics that are continuous liquid jet and modulated liquid jet. The experiments were conducted using water, over a range of crossflow velocities from $42{\sim}l36\;m/s$, with modulation frequencies of $35.7{\sim}166.2\;Hz$. Between continuous crossflow jet and modulated cross-flow jet of penetration, breakup point, spray angle and macro spray shape are experimentally investigated with image analysis. In cross-flow field, main parameter of liquid jet for breakup was cross-flow stream rather than modulation effect. As oscillation of the periodic pressure that could make liquid jet moved up and down, the mixing efficiency was increased. Also, a bulk of liquid jet puff was detected at upper field of liquid surface. So, this phenomenon has a good advantage of mixing spray from concentration of center area to outer area. Because of modulation frequency, SMD inclination of the structured layer was evanescent. Cross-sectional characteristics of SMD at downstream area were non-structured distributions. Then cross-sectional characteristics of SMD size were about same tendency over a range that is effect of spray mixing. The tendency of volume flux value for various modulation frequency was same distribution. And volume flux was decreased when the modulation frequency increase.

• Journal of ILASS-Korea
• /
• v.7 no.3
• /
• pp.38-44
• /
• 2002

The purpose of this study is to investigate the effect of the volume fraction of water and injection pressure on the spray characteristics of water/oil emulsified fuel injected from the pressure swirl atomizer. The mixture of light oil and water by using impeller mixer was performed. The spray characteristics such as SMD and velocity were measured using PDPA. The injection pressures were 7.5, 100, 200 and $300kgt/cm^2$ and volume fractions of water in emulsified fuel were 0, 10, 20 and 30%, respectively. The measurement sections were at 30, 60 and 90mm from injection nozzle tip. SMD and velocity of emulsified fuel were larger gradually by increasing the volume fraction of water in emulsified fuel. The spray angle was decreased and axial velocity was increased with increase in water content. It was found that the relative SMD ratio was increased more greatly than the relative axial velocity ratio in super critical pressure. The relative SMD ratio was increased and the relative axial velocity ratio was decreased with increase injection pressure at spray downstream.

• Journal of Korean Society of Water and Wastewater
• /
• v.14 no.2
• /
• pp.147-156
• /
• 2000

In this study, the optimal operation parameters of MLE(Modified Ludzack-Ettinger) process treating the liquid supernatant separated from the slurry excreta of swine feedlot was studied as a promising biological treatment process. The nitrogen removal characteristics with different volume ratio between nitrification and denitrification reactor and the operational effect with different nitrogen loading rate, and different C/N($COD_{Cr}/TKN$) ratio were investigated. Based on the laboratory results, pilot MLE plant was operated to examine the effect of ambient temperature for five months including winter. The denitrification reactor which is 20% of total volume was proposed as the most optimal volume fraction for nitrification and denitrification. The optimum ratios of F/M and $F_N/M$ were increased with increase of the C/N ratio. However, optimum F/M ratio was changed more rapidly than $F_N/M$ ratio with increase of the C/N ratio. Therefore, MLE process is desirable to be controlled by F/M ratio in the range of high C/N ratio and by $F_N/M$ ratio in the range of low C/N ratio. Pilot MLE plant showed the higher removal efficiencies of COD and TKN in winter than in summer and was operated most stably at the temperature of $20{\sim}25^{\circ}C$ for mixed liqour.

• The Journal of Asian Finance, Economics and Business
• /
• v.7 no.10
• /
• pp.95-107
• /
• 2020

This study analyzes the effect of corporate social responsibility (CSR) activity on investors' heterogeneous beliefs. The hypothesis of this study is based on the conflicting effects of CSR activities on firm value and earning's quality. Investors' heterogeneous beliefs used in the empirical analysis of this study are trading volume, and CSR activity is measured by the KEJI Index (Korea Economic Justice Institute Index). This study performs an empirical analysis using regression analysis including control variables. CSR activities are found to have a positive relationship with trading volume. This is consistent regardless of the low and high accounting information (earning's quality). It can be interpreted that Korea's CSR activity acts as an incentive to increase investors' heterogeneous beliefs about target companies. In other words, it implies that the investor judges CSR activities negatively when evaluating firm value. This study could have a policy implication in that it analyzes how CSR activities affect investors' decision-making. In other words, this study analyzed CSR activities from the perspective of shareholders. Therefore, this study is expected to provide useful information for policymaking by regulatory agencies. In particular, its contribution is to presents data that CSR activities can be a negative factor in evaluating firm values.

• Journal of Korean Society of Forest Science
• /
• v.86 no.4
• /
• pp.450-458
• /
• 1997

It is inadequate to compare operating costs between some logging machines with a low rate of utilization of them except the effect of operating time. The operating volume to maximize the utilization of the logging machines is different from each other, thus it is important to choose the proper logging machines and operating system according to the size of logging management. This study presents one of the methods to choose the economical optimum logging machines according to the operating volume to promote the economical efficiency of the machines. In order to go ahead with the Korean forestry mechanization plan, it should be considered which machine or operating system has the economical priority and if it can be suitable to the effect of wage increment.

• Composites Research
• /
• v.28 no.6
• /
• pp.366-371
• /
• 2015

In order to improve the mechanical properties of tungsten at room and elevated temperature, hafnium carbide (HfC) reinforced tungsten matrix composites were prepared using the spark plasma sintering technique. The effect of HfC content on the compressive strength and flexural strength of the tungsten composites was investigated. Mechanical properties of the composites were also measured at elevated temperatures and their trends, with varying reinforcement volume fraction, were studied. The effect of reinforcement fraction on the thermal properties of the composites was investigated. The thermal conductivity and diffusivity of the composites decreased with increasing temperature and reinforcement volume fraction. An inherently low thermal conductivity of the reinforcement as well as interfacial losses was responsible for lower values of thermal conductivity of the composites. Values of coefficient of thermal expansion of the composites were observed to increase with HfC volume fraction.