• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.147-152
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• 1999

The purpose of this study is to offer foundmental information of fly ash concrete for field application. Through before study of fly ash concrete, various properties were checked. but when fly ash was added In concrete, entrained air quantity was decreased as fly ash substitution is increased in fresh concrete. so entrained air(below AE) quantity and a kind of AE according to fly ash substitution was tested basic properties. Also water-reducing efficiency was tested. And hydration heat according to fly ash substitution was tested by KR-100. As result of test, according to fly ash substitution increase, entrained air quantity is increase for target entrained air quantity, water-reducing efficiency and hydration heat are positive.

• Particle and aerosol research
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• v.10 no.4
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• pp.155-162
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• 2014

The internal temperature will change depending on operation conditions and material of cyclone dust collector. This study compares the results of collection efficiency and temperature distribution on the different heat flux at wall of dust collector. The previous researcher's experiment results were used to confirm the reliability of CFD(Computational Fluid Dynamics) model. Based on this verified CFD model, we extended the analysis on the cyclone dust collectors. In CFD study, we used RNG k-epsilon model for analysis of turbulence flow, fluid is air, the velocity at inlet is 10 m/s, the temperature of air is $600^{\circ}C$. Because of the difference of outer vortex and inner vortex temperature, the collection efficiency will reduce with the increase of heat flux, showed the highest collection efficiency at heat insulation.

• Journal of Power Electronics
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• v.11 no.2
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• pp.194-201
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• 2011

The air flow supplied to a fuel cell system is one of the most significant factors in determining fuel efficiency. The conventional method of controlling the air flow is to fix the oxygen supply at an estimated constant rate for optimal efficiency. However, the actual optimal point can deviated from the pre-set value due to temperature, load conditions and so on. In this paper, the maximum efficiency point tracking (MEPT) algorithm is proposed for finding the optimal air supply rate in real time to maximize the net-power generation of fuel cell systems. The fixed step MEPT algorithm has slow dynamics, thus it affects the overall efficiency. As a result, the variable step MEPT algorithm is proposed to compensate for this problem instead of a fixed one. The complete small signal model of a PEM Fuel cell system is developed to perform a stability analysis and to present a design guideline. For a design example, a 1kW PEM fuel cell system with a DSP 56F807 (Motorola Inc) was built and tested using the proposed MEPT algorithm. This control algorithm is very effective for a soft current change load like a grid connected system or a hybrid electric vehicle system with a secondary energy source.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.71-76
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• 2001

An electret filter is composed of permanently charged electet fibers and is widely used in applications requiring high collection efficiency and low-pressure drop. In this work, the collection efficiency of the filter media used in manufacturing cabin air filters was investigated by using poly-disperse particles when submicron particles are loaded. Long-term experiments were conducted by applying different charging states, which are spray electrification and charge equilibrium by bipolar ionization. In order to investigate on the effect of particle loading in filter media, NaCl particles were generated from 0.1% and 1% solutions by an atomizer. In NaCl 0.1%, the collection efficiency of electret filter decreased and then did not change in equilibrium state. In the case of relative larger particles of NaCl 1%, collection efficiency for the equilibrium charged particles increases due to the particle loading on the filter fibers. Particles charged by spray electrification are small in collection efficiency after equilibrium state and increase of filter media's pressure drop was very low in comparison of the equilibrium charged particles.

• Journal of Advanced Marine Engineering and Technology
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• v.21 no.4
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• pp.421-429
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• 1997

This study is theoretically examined the influences on the performance of diesel engine super¬charged by exhaust gas turbine with the change of excess air factor, admission ratio, total efficien¬cy of turbine and compressor, scavenging pressure ratio, and scavenging temperature. In this study, all calculations are carried out by computer, and the theoretical engine performance is com¬pared with the actual engine performance which is offered from engine manufacturer. Following results are acquired by this study. The mean effective pressure is increased with decrease of excess air factor or increase of scavenging pressure ratio. As the admission ratio or total efficiency of tur¬bine is increased, the mean effective pressure is increased but the specific fuel consumption is decreased. Mean calculation error compared with the actual engine performance is under 5 per¬cents, therefore, this calculation method can be used in the design of diesel engine.

• Journal of Korean Society for Atmospheric Environment
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• v.31 no.1
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• pp.54-62
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• 2015

Small scale paint overspray booths are being operated nationwidely, for repair of passenger car body parts. paint aerosols are emitted from the paint overspray booth in operations. In paint overspray booth operations without ventilation system and air pollutants collection unit, it may land on nearby equipment. In this study a removal of sticky paint aerosol for application of the small-scale overspray paint booth. it's cause the surface of filter bag from generated sticky paint aerosol. To remove adhesion of paint aerosol the agglomerating agents are injected and mixed with sticky paint aerosols prior to reach the filter bag. The paint spray rate was set as $10{\pm}5g/min$ from air-atomized spray guns in the spray booth, injection rate of agglomerating was $10{\pm}5g/min$ in the mixing chamber. The filtration velocity including air pollutants varied from 0.2 m/min to 0.4 m/min. Bag cleaning air pressure was set as $5.0kg_f/min$ for detaching dust cake from surface of filter bag. Bag cleaning interval at the filtration velocity of 0.2 m/min was around 3 times longer than that of the 0.4 m/min. The residual pressure drop maintained highest value at the highest filtration velocity. Fractional efficiency of 99.952%~99.971% was possible to maintain for the particle size of 2.5 microns. Total collection efficiency at the filtration velocity of 0.2 m/min was 99.42%. During this study we could confirm high collection efficiency and long cleaning intervals for the test with filtration velocity of 0.2 m/min indicating an optimal value for the given dimensions of the test unit and test operating conditions.

• Journal of Power System Engineering
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• v.17 no.5
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• pp.58-63
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• 2013

In this study, the effect of deep ocean condenser inlet temperature ($T_{DOI}$), condenser inlet pressure ($P_{cond,in}$), and thermal diffusivity on system efficiency of some selected refrigerants was analyzed using HYSYS. The proposed DOTEC cycle is similar to the reheat Rankine cycle but eliminates irreversibilities by bleeding a fraction of the steam between certain stages of the turbine. The evaporator inlet mass flow rate, inlet temperature of turbine 1, turbine efficiency and inlet and outlet temperature of heat source were imposed. The working fluids considered are sorted in ascending order of their molecular weights as R717, R600a and R152a. Results indicated that a fluid with a lower boiling point temperature like R717 needs a corresponding high heat source and/or evaporator inlet pressure. Also, the response of thermal diffusivity closely follows the change in TDOI as an increase in $T_{DOI}$ increases $P_{cond,in}$ which reduces thermal diffusivity and system efficiency. Furthermore, the fluid with the nominal boiling point temperature has the highest efficiency with efficiency decreasing with an increase in TDOI.

• Quality Improvement in Health Care
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• v.7 no.1
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• pp.72-89
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• 2000

Background : Various types of protective footwear have been used to minimize bacterial contamination in operating rooms. In recent years, debate has arisen concerning the need for use of such protective footwear. This study was designed to provide useful data about choosing shoes most suitable for the surgical environment. Methods : Between November, 1999 and January, 2000, we performed this experimental study by comparing effect of three types of shoes (i.e., disposable shoescover, operating room-restricted shoes, and ordinary shoes) on bacterial contamination of operating rooms equipped with two different ventilation systems (i.e., high air-change, low air-change) respectively. Data were collected during two- hour sham operations in which subjects and their activities were strictly standardized. Bacterial flora were sampled from the study area floor and air colony counts were measured. Results : In experiments involving high air-change ventilation system, there was a significant difference of floor contamination between three types of shoes, but no difference of air contamination. Under low air-change system, there was a significant difference of both floor and air contamination between three types of shoes. Conclusion : The results show that protective footwear would be unnecessary in the operating room with high air-change ventilation system, but it is important to choose suitable shoes carefully under low air-change system. Therefore, the use of outdoor shoes can be considered under high air-change system, but it would seem sensible to apply their first use in less bloody operations at the day surgery center or out-patient department to prevent transfer of body fluid into the outside environment.

• Journal of the Korean Society of Visualization
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• v.19 no.1
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• pp.94-99
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• 2021

In order to increase the efficiency of thermoelectric refrigerators using the Peltier effect, it is necessary to optimize the distribution of the flow of cold air from the fan. In this study, the flow flowing upwards and downwards while changing the area of the flow path was visualized using the PIV technique for the control of cold air in a thermoelectric refrigerator. From these results, the flow rate according to the change in the area of the flow path was confirmed, and design criteria for optimizing the distribution of cold air flowing to the top and bottom of the refrigerator were suggested.

• Journal of Power System Engineering
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• v.17 no.1
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• pp.58-63
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• 2013

The aerodynamic performance of double inlet sirocco fan is strongly dependent upon the design factors of impeller and scroll. In this paper, the change of scroll size was adopted to investigate the aerodynamic performances of double inlet sirocco fan and indoor PAC. Especially, a scroll expansion angle and a cut-off clearance ratio were considered to change the scroll size. In addition, the installation depth between double inlet sirocco fan and indoor PAC was considered. As a result, the total pressure efficiency of double inlet sirocco fan shows about 62%~73% according to the change of scroll expansion angles. Moreover, the flowrate performance of indoor PAC is the best at the condition of a scroll expansion angle of 8°, an installation depth of 15 mm and a cut-off clearance ratio of 8%.