• 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 electromagnetic engineering and science
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• v.18 no.2
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• pp.88-93
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• 2018

Radio frequency (RF) and microwave power is one of the key quantities in the framework of electromagnetic measurement standards. Therefore, the stability of the power standard is essential to users' reliable measurements in various areas. Coaxial and waveguide thermistor mounts are used as transfer standards of RF and microwave power. Over decades, the effective efficiencies of thermistor mounts have been measured using coaxial and waveguide microcalorimeters in the frequency range of 10 MHz-40 GHz. The measurement uncertainty of the effective efficiency is evaluated. Results show that the power standards have been well maintained within the measurement uncertainty.

• Journal of Power Electronics
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• v.15 no.2
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• pp.319-326
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• 2015

In this paper, a cost-effective single switch multi-channel LED (light emitting diode) driver is proposed. While conventional LED drivers require as many non-isolated DC/DC converters as the number of LED channels, the proposed LED driver needs only one power switch and several balancing capacitors instead of expensive non-isolated DC/DC converters. Therefore, the proposed driver features a simpler structure, with a lower cost and a higher efficiency. Because its power switch can be turned off under the zero current switching condition, it has very desirable advantages such as improved electromagnetic interference characteristics and high efficiency. Moreover, it uses only a small number of DC blocking capacitors with no additional active devices for the current balancing of multi-channel LEDs. As a result, the proposed driver exhibits high reliability and is cost effective. To confirm the validity of the proposed driver, a theoretical analysis is performed, and design considerations and experimental results obtained from a prototype that is applicable to a 46" LED-TV are presented.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.417-422
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• 2006

On trends of 'well-being', heat recovery ventilators(HRV) are recently installed in high rise buildings. HRV is not energy saving instrument but ventilating one. But many people have not been aware of the accurate fact. In this study, performances of HRV are tested under foreign and domestic standards. Especially air-tightness is measured three times by using gas concentration method and pressing equipment. Wet effective ventilating air volume is acquired by solving gas concentration equations. After research air-tightness and effective ventilating air volume must be more focused on than heat transfer efficiency to select the optimal HRV. Heat transfer efficiency must be adjusted by air-tightness results.

• Korean Management Science Review
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• v.32 no.3
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• pp.37-54
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• 2015

This paper suggests energy efficiency which can be the foundation on corporate profit and effective energy management following by change of global climate and of energy-related regulations. Using comparable financial information and information related to energy use, an DEA (Data Envelopment Analysis) model has been used to identify energy efficiency with DMU (Decision Making Unit)s which are companies subjected to reduce greenhouse gas emission in 2009. Through this research, different from existing researches, environmental variables which can influence on energy efficiency are identified. The results show as follows. First, most of companies follow IRS, which means scale of economy exists among units so that they have more opportunity to increase efficiency by increasing scale of inputs. Second, this research identified that depending on the difference of environmental characters such as the emission structure and the size of companies, energy efficiency of the companies turns out differently.

• KIEAE Journal
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• v.2 no.3
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• pp.11-16
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• 2002

Indoor air environment is one of the most important factors that affect resident's health and comfort level. In this paper, the influence of ventilation efficiency with different types of furniture arrangement at breathing zone in a room was analyzed by numerical simulation based on computational fluid dynamics(CFD). The furniture layout of students' bedroom have been classified by three different patterns so that SVE3(scale for ventilation efficiency3) in the rooms was analyzed for air flow distribution. According to the results of the study, SVE3 has the maximum value in spaces between furnitures and each comer of the room. The furniture arrangement influences the ventilation efficiency. It was con finned that ventilation effective in a room is not uniformly distributed as compared the breathing zone with all the area in a room. It means that a study of ventilation efficiency was considered relatively with target zone(a residential or breathing zone) and all the area in a space.

• New & Renewable Energy
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• v.5 no.3
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• pp.32-39
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• 2009

The Samcheonpo ocean small hydropower plant (SHP) has a special feature of using marginal hydraulic head of circulating water system of fossil fuel power plant as a power source and having the characteristics of general hydropower generation and tidal power generation as well. Also, it contributes to reducing green house gases and developing clean energy source by recycling circulating water energy otherwise dissipated into the ocean. The efficiency of small hydropower plant is directly affected by effective head and flow rate of discharged water. Therefore, the efficiency characteristics of ocean hydropower plant are analyzed with the variation of water level and flow rate of discharged water, which is based on the accumulated operation data of the Samcheonpo hydropower plant. After the start of small hydropower plant operation, definite rise of water level was observed. As a result of flow pattern change from free flow to submerged flow, the instability of water surface in overall open channel is increased but it doesn't reach the extent of overflowing channel or having an effect on circulation system. Performance evaluation result shows that the generating power and efficiency of small hydropower exceeds design requirements in all conditions. Analysis results of CWP's water flow rate verify that the amount of flowing water is measured less and the highest efficiency of small hydropower plant is achieved when the effective head has its maximum value. In conclusion, efficiency curve derived from water flow rate considering tidal level shows the best fitting result with design criteria curve and it is verified that overall efficiency of hydropower system is satisfactory.

• Journal of Korean Society of Water and Wastewater
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• v.31 no.2
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• pp.125-139
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• 2017

In this paper, the performance of a synthetic fiber filter aimed at high-speed operation and dosed with different coagulants or filter aids was investigated. Without a coagulant, the filter efficiency was about 62% which was greatly enhanced when three types of coagulants namely PAC, Alum, and $FeCl_3$ were used. Among the coagulants tested, PAC was the most effective, giving 91% filter efficiency, followed by Alum with 90%, and $FeCl_3$ with 78%. PAC worked effectively at a very small range of dose, but Alum was relatively effective in a wide range of concentration. Compared with PAC and Alum, $FeCl_3$ provided more or less contant efficiency regardless of its dose but gave the poorest filter efficiency. Moreover, as the inflow turbidity increased, headloss increased and the efficiency decreased at any dose and type of coagulant. The headloss recorded in this particular synthetic fiber filter is not significant as compared to that observed in typical granular filters. The recovery of solids estimated after filter cleaning was about 80% for both PAC and Alum, but poorer at 72% in the case of $FeCl_3$ due to the heavy and large floc characteristics. The recurrence of filter efficiency verified through repetitive filter runs was found to be satisfactory.

• Wind and Structures
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• v.7 no.4
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• pp.235-250
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• 2004

The current study reports the results of an experimental program conducted on a structure fitted with a liquid damper (TLD) and subjected to harmonic excitation. Screens were placed inside the TLD to achieve the required inherent damping. In the first part of the study, reduced scale models of the building-TLD systems were tested under two levels of excitation. The efficiency of the damper was assessed by evaluating the effective damping provided to the structure and comparing it to the optimum effective damping value, provided by a linear tuned mass damper (TMD). An extensive parametric study was then conducted for one of the three models by varying both the excitation amplitude and the tuning ratio, defined as the ratio of the TLD sloshing frequency to the natural frequency of the structure. The effectiveness and robustness of a TLD with screens were assessed. Results indicate that the TLD can be tuned to achieve a robust performance and that its efficiency is not significantly affected by the level of excitation. Finally, the equivalent amplitude dependent TMD model, developed in the companion paper is validated using the system test results.

• Journal of Information Technology and Architecture
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• v.11 no.1
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• pp.75-80
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• 2014

At the time the interest and love of the Korean professional baseball is increasing, the need for effective recruiting method rising. Recruiting existing methods were scheme based on expert evaluation, to obtain the players of each team. However, the existing method does not reflect only objective rating but also subjective way of school tie and delays are effect. Therefore the conventional method could not be the efficient. Therefore this paper analyze Korea baseball player's efficiency based on entire team and each team by using DEA (Data Envelopment Analysis) method, and use this efficiency to discuss effective way of recruiting players. Finally, the validity of experiment is confirmed by the matters of actual sell of players who are scouted by experiment.