• Journal of Electrical Engineering and Technology
• /
• v.8 no.5
• /
• pp.1175-1181
• /
• 2013

The aim of this paper is to design and evaluate a high concentration, high penetration unipolar corona ionizer. The electrostatic characteristics in terms of voltage-current relationships of the present ionizer in the discharge zones for positive and negative coronas were discussed. Using ion current measurement, the concentration and penetration of ions were evaluated at corona voltages across the needle electrodes between 1 and 4 kV, flow rates between 1 and 5 L/min, and an operating pressure of 1 atm. In the discharge zone of the ionizer, the highest ion concentrations were found to be about $1.71{\times}10^{14}$ and $5.09{\times}10^{14}\;ions/m^3$ for positive and negative coronas, respectively. At the outlet of the ionizer, it was found that the highest ion concentration was about $1.95{\times}10^{13}$ and $1.91{\times}10^{13}\;ions/m^3$ for positive and negative coronas, respectively. The highest ion penetration for positive and negative coronas through the ionizer was found to be about 98 % and 33 %, respectively. The $N_it$ product for positive and negative coronas was also found to $1.28{\times}10^{13}$ and $7.43{\times}10^{13}\;ions/m^3s$, respectively. From the findings, this ionizer proved to be particularly useful as an aerosol charger for positive and negative charge before the detector in an electrical aerosol detector.

• Journal of the Korea Concrete Institute
• /
• v.14 no.1
• /
• pp.100-109
• /
• 2002

Significant damage to concrete results from the intrusion of corrosive solutions, for example, dissolved chlorides corrode reinforcing steel and cause spatting. Effectively blocks the penetration of these solutions will eliminate or greatly reduce this damage and lead to increased durability. This study is to investigate the effects of pozzolanic admixtures, fly ash and silica fume, and a blast furnace slag on the chloride ion penetration of concretes. The main experimental variables wore the water-cementitious material ratios, the types and amount of admixtures, and the curing time. And it is tested for the porosity and pore size distributions of cement paste, chloride ion permeability based on electrical conductance, and 180-day ponding test for chloride intrusion. The results show that the resistance of concrete to the penetration of chloride ions increases as the w/c was decreased, and the increasing of curing time. Also, concrete with pozzolans exhibited higher resistance to chloride ion penetration than the plain concrete. The significant reduction in chloride ion permeability(charge passed) of concrete with pozzolans due to formation of a discontinuous macro-pore system which inhibits flow. It is shown that there is a relationship between chloride ion permeability and depth of chloride ion penetration of concrete, based on the pore structure (porosity and pore size distributions) of cement paste.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.15 no.2
• /
• pp.1-7
• /
• 2007

The effect of injector geometries including the injection angle and number of nozzle holes on homogeneous charge compression ignition (HCCI) engine combustion has been investigated in an automotive-size single-cylinder diesel engine. The HCCI engine has advantages of simultaneous reduction of PM and NOx emissions by achieving the spatially homogenous distribution of diesel fuel and air mixture, which results in no fuel-rich zones and low combustion temperature. To make homogeneous mixture in a direct-injection diesel engine, the fuel is injected at early timing. The early injection guarantees long ignition delay period resulting in long mixing period to form a homogeneous mixture. The wall-impingement of the diesel spray is a serious problem in this type of application. The impingement occurs due to the low in-cylinder density and temperature as the spray penetrates too deep into the combustion chamber. A hole-type injector (5 holes) with smaller angle ($100^{\circ}$) than the conventional one ($150^{\circ}$) was applied to resolve this problem. The multi-hole injector (14 holes) was also tested to maximize the atomization of diesel fuel. The macroscopic spray structure was visualized in a spray chamber, and the spray penetration was analyzed. Moreover, the effect of injector geometries on the power output and exhaust gases was tested in a single-cylinder diesel engine. Results showed that the small injection angle minimizes the wall-impingement of diesel fuel that results in high power output and low PM emission. The multi-hole injector could not decrease the spray penetration at low in-cylinder pressure and temperature, but still showed the advantages in atomization and premixing.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.15 no.2
• /
• pp.1188-1194
• /
• 2014

The purpose of this study is to estimate Chloride Attack Resistibility and mechanical properties of quaternary concrete adding fly ash, blast-furnace slag, and silica fume. Compressive strength, modulus of elasticity, chloride migration coefficient, charge passed from Rapid chloride penetration test(RCPT), and immersion testing in 3% NaCl are tested. Chloride migration coefficient and charge passed of quaternary concrete measured $0.032{\times}10^{-12}m^2/sec$ and 650 coulomb at 17 weeks, which are in a permitted limit. Also in immersion test, depth of chloride penetration and maximum chloride ion of quaternary concrete measured 3.7 mm and $10.211kg/m^3$ respectively. From the results, quaternary concrete adding fly ash, blast-furnace slag, and silica fume denotes improvement of mechanical properties and chloride attack resistibility.

• Journal of Digital Convergence
• /
• v.2 no.2
• /
• pp.63-76
• /
• 2004

There is a considerable gap in the level of the Internet access charges among countries because of the history of the Internet use, current status of the Internet infrastructure, the Internet penetration rate, and so on. Low Internet access charge increases the number of the Internet users and the Internet penetration rate, which boosts economic activities. This paper empirically explores the impacts of the internet access charges on economic activities using a cross-country analysis based on data from 76 countries for the year 1998-2001. To this end, several versions of the neoclassical growth models, explicitly including the internet access charges, are estimated with the GDP used for a proxy for economic activities and the level of Internet access charges considered as an input to production. Subject to the appropriate caveats, the results show that the level of the Internet access charges make a significantly negative effect on economic activities. In other words, it is concluded that low Internet access charges of a county increase economic activities and the increased economic activities in turn raise the real income of the county.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.553-556
• /
• 2008

We have studied about chloride penetration test by electrical conductance to 10 specimens made from same test batch. The coefficient of variation of total passed charge(Colombs) was about 24% in same specimens, and we draw a conclusion this method has a low reliability. Owing to complicated reaction ; heterogeneous material, mixing error and error of testing method, then we must consider the scope of the error which is introduced. Specially when you trying to get one test result against one spcimen, you can commit a big error, therefore we recommend that you use mean value against 3 specimens at least.

• Journal of the Korea Concrete Institute
• /
• v.29 no.3
• /
• pp.307-314
• /
• 2017

Concrete is a durable and cost-benefit construction material, however performance degradation occurs due to steel corrosion exposed to chloride attack. Penetration of chloride ion usually decreases due to hydrates formation and reduction of pores, and the reduced chloride behavior is considered through decreasing diffusion coefficient with time. In the work, HPC (High Performance Concrete) samples are prepared with 3 levels of W/B (water to binder) ratios of 0.37, 0.42, and 0.27 and 3 levels of replacement ratios of 0%, 30% and 50%. Several tests containing chloride diffusion coefficient, passed charge, and compressive strength are performed considering age effect of 28 days and 180 days. Chloride diffusion is more reduced in OPC concrete with lower W/B ratio and GGBFS concrete with 50% replacement ratio shows significant reduction of chloride diffusion in higher W/B ratio. At the age of 28 days, GGBFS concrete with 50% replacement ratio shows more rapid reduction of chloride diffusion than strength development, which reveals that abundant GGBFS replacement has effective resistance to chloride penetration even in the early-aged condition.

• Journal of the Korea Institute of Building Construction
• /
• v.22 no.1
• /
• pp.35-43
• /
• 2022

The aim of this work was to a comparative review the performance of high calcium silicate cement (HSCSC) and that of ordinary Portland cement(OPC) and blast furnace slag cement(S/C). The result of the compressive test confirmed that the compressive strength development rate of high calcium silicate cement concrete at the age of 3 days was 73.6% that of ordinary Portland cement concrete. However, at the age of 28 days, the strength development rate of high calcium silicate cement increased to about 107.0% compared to ordinary Portland cement. In addition, the test of the chloride ion penetration resistance of concrete showed that at the age of 28 days, the passed charge decreased by 73.4% and 93.0%, respectively, in blast furnace slag cement and high calcium silicate cement compared to ordinary Portland cement, and at the age of 56 days, it decreased by 79.1% and 98.3%, exhibiting excellent resistance to chloride ion penetration. In particular, it was confirmed that the rate of decrease in the passed charge with age was higher in high calcium silicate cement than in ordinary Portland cement and blast furnace slag cement.

• Korean Journal of Materials Research
• /
• v.1 no.3
• /
• pp.125-131
• /
• 1991

Boron penetration phenomenon of $p^{+}$ silicon gate with as-deposited amorphous or polycrystalline Si upon high temperature annealing was investigated using high frequency C-V (Capacitance-Volt-age) analysis, CCST(Constant Current Stress Test), TEM(Transmission Electron Microscopy) and SIMS(Secondary Ion Mass Spectroscopy), C-V analysis showed that an as-deposited amorphous Si gate resulted in smaller positive shifts in flatband voltage compared wish a polycrystalline Si gate, thus giving 60-80 percent higher charge-to-breakdown of gate oxides. The reduced boron penetration of amorphous Si gate may be attributed to the fewer grain boundaries available for boron diffusion into the gate oxide and the shallower projected range of $BF_2$ implantation. The relation between electron trapping rate and flatband voltage shift was also discussed.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.12 no.5
• /
• pp.32-39
• /
• 2004

HCCI (Homogeneous Charge Compression Ignition) combustion has a great advantage in reducing NOx (Nitrogen Oxides) and PM (Particulate Matter) by lowering the combustion temperature due to spontaneous ignitions at multiple sites in a very lean combustible mixture. However, it is difficult to make a diesel-fuelled HCCI possible because of a poor vaporability of the fuel. To resolve this problem, the two-stage injection strategy was introduced to promote the ignition of the extremely early injected fuel. The compression ratio and air-fuel ratio were found to affect not only the ignition, but also control the combustion phase without a need for the intake-heating or EGR (Exhaust Gas Recirculation). The ignition timing could be controlled even at a higher compression ratio with increased IMEP (Indicated Mean Effective Pressure). The NOx (Nitrogen Oxides) emission level could be reduced by more than 90 % compared with that in a conventional DI (Direct Injection) diesel combustion mode, but the increase of PM and HC (Hydrocarbon) emissions due to over-penetration of spray still needs to be resolved.