• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 2000년도 춘계 학술발표회 논문집
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• pp.201-207
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• 2000

This study was carried out to optimize burner and heat exchanger of the condensing gas boiler which can save energy by utilizing latent heat of combustion gas and reduce pollutant in exhaust gas. The heat exchanger of the gas boiler was composed of three parts, which were an upper. lower , and coil heat exchanger . The upper heat exchanger was placed outside of the premixed burner and a lower heat exchanger was located under the upper heat exchanger. And, coil heat exchanger rounded the outer surface of an upper and lower heat exchanger. The boiler designed by this research reaches turn-down ratio 4 : 1 in the domain of equivalence ratio 0.75-0.8 and thermal efficiency of 97% . Emission of NOx and CO concentration was under 20ppm and 140ppm at equivalence ratio 0.8 . When diameter of the burner replace 60mm by 50mm. emission of CO was reduced about 50ppm remarkably.

• 한국수소및신에너지학회논문집
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• 제15권4호
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• pp.348-354
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• 2004

Hydrogen gas has several merits such as lower ignition energy, wide flammability and shorter quenching distance. It leads to high thermal efficiency but backfire occurrence. In this study, feasibility of expansion of BFL(Back-Fire Limit) equivalence ratio and combustion characteristics by a dilution of hydrogen fuel are experimently examined by using experimental heavy duty single cylinder hydrogen fueled engine. As results, it is found that BFL equivalence ratio is expanded to rich range and torque is increased.

• 설비공학논문집
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• 제27권9호
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• pp.455-462
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• 2015

Residential buildings account for a significant portion of the total building-energy usage in Korea, and a variety of research studies on the domestic boiler have therefore been carried out; however, most of these studies examined the boiler itself, whereby the part-load ratio characteristics and the corresponding gas-energy consumption patterns were not analyzed. In this study, the part-load ratio and operating characteristics of a domestic gas boiler were analyzed within a residential building equipped with a radiant floor-heating system; in addition, the energy consumption between condensing and conventional boilers was comparatively analyzed. Our results show that significant portions of the total operating hours, heating load, and energy consumption are in the part-load ratio range of 0 through 40%, whereby the energy consumption was significantly affected by the boiler efficiency under low part-load conditions. These results indicate that the part-load operation of a boiler is an important factor in residential buildings; furthermore, replacing a conventional boiler with a condensing boiler can reduce annual gas-energy usage by more than 20%.

• Journal of Power Electronics
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• 제15권6호
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• pp.1468-1479
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• 2015

Renewable energy resources such as wind and photovoltaic power generation systems demand a high step-up DC-DC converters to convert the low voltage to commercial grid voltage. However, the high step-up converter using a transformer has limitations of high voltage stresses of switches and diodes when the transformer winding ratio increases. Accordingly, conventional studies have been applied to series-connect multioutput converters such as forward-flyback and switched-capacitor flyback to reduce the transformer winding ratio. This paper proposes new single-ended converter topologies of an isolation type and a non-isolation type to improve power efficiency, cost-effectiveness, and output ripple. The first proposal is an isolation-type charge-pump switched-capacitor flyback converter that includes an extreme-ratio isolation switched-capacitor cell with a chargepump circuit. It reduces the transformer winding number and the output ripple, and further improves power efficiency without any cost increase. The next proposal is a non-isolation charge-pump switched-capacitor-flyback tapped-inductor boost converter, which adds a charge-pump-connected flyback circuit to the conventional switched-capacitor boost converter to improve the power efficiency and to reduce the efficiency degradation from the input variation. In this paper, the operation principle of the proposed scheme is presented with the experimental results of the 100 W DC-DC converter for verification.

• Journal of Electrical Engineering and Technology
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• 제8권6호
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• pp.1400-1408
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• 2013

This paper proposes a new grid-tied power converter for battery energy storage, which is composed of a 2-stage DC-DC converter and a PWM inverter. The 2-stage DC-DC converter is composed of an LLC resonant converter connected in cascade with a 2-quadrant hybrid-switching chopper. The LLC resonant converter operates in constant duty ratio, while the 2-quadrant hybrid-switching chopper operates in variable duty ratio for voltage regulation. The operation of proposed system was verified through computer simulations. Based on computer simulations, a hardware prototype was built and tested to confirm the technical feasibility of proposed system. The proposed system could have relatively higher efficiency and smaller size than the existing system.

• 대한설비공학회지:설비저널
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• 제23권2호
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• pp.77-83
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• 1994

• Journal of Power Electronics
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• 제16권6호
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• pp.2035-2044
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• 2016

In order to match the voltages between high voltage battery stacks and low voltage super-capacitors with a high conversion efficiency in hybrid energy sources electric vehicles (HESEVs), a high ratio bidirectional DC-DC converter with a synchronous rectification H-Bridge is proposed in this paper. The principles of high ratio step-down and step-up operations are analyzed. In terms of the bidirectional characteristic of the H-Bridge, the bidirectional synchronous rectification (SR) operation is presented without any extra hardware. Then the SR power switches can achieve zero voltage switching (ZVS) turn-on and turn-off during dead time, and the power conversion efficiency is improved compared to that of the diode rectification (DR) operation, as well as the utilization of power switches. Experimental results show that the proposed converter can operate bidirectionally in the wide ratio range of 3~10, when the low voltage continuously varies between 15V and 50V. The maximum efficiencies are 94.1% in the Buck mode, and 93.6% in the Boost mode. In addition, the corresponding largest efficiency variations between SR and DR operations are 4.8% and 3.4%. This converter is suitable for use as a power interface between the battery stacks and super-capacitors in HESEVs.

• 한국수소및신에너지학회논문집
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• 제23권3호
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• pp.274-284
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• 2012

Recently, gasification technology for coal blended with biomass has been an issue. Especially, An advantages of coal blended with biomass are 1) obtaining high cold gas efficiency, 2) obtaining syn-gas of high-high heating value (HHV), and 3) controlling occurrence of $CO_2$. In this study, the efficiency and characteristic of 300 MW Shell type gasifier were predicted using CFD simulation. The CFD simulation was performed for biomass coal blending ratios of 0~0.2, 0.5, 1 and $O_2$/fuel ratios of 0.5~0.84. Kinetic parameters (A, $E_a$) obtained by $CO_2$ gasification experiment were used as inputs for the simulation. In results of CFD simulation, residence times of particle in 300MW Shell type gasifer presented as 7.39 sec ~ 13.65 sec. Temperature of exit increased with $O_2$/fuel ratio as 1400 K ~ 2800 K, while there is not an effects of biomass coal blending ratios. Considering both aspects of temperature for causing wall slagging and high cold gas efficiency, the optimal $O_2$/fuel ratio and blending ratio were found to be 0.585 and 0.05, respectively.

• 한국습지학회지
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• 제23권3호
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• pp.234-241
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• 2021

본 논문은 자유수면을 갖는 와류수차의 성능에 풀리의 영향을 이해하는 것이다. 실험은 개수로 유입구 유량 0.0069 ~ 0.0077 m³/s 범위에서 물리적 인자(와류높이, 유속, 유효낙차 등)에 따른 수차의 회전수, 전압 및 전류를 측정해 분석하였다. 실험결과에 따르면 와류수차의 전압, 전류 및 회전수는 블레이드 형태와 상관없이 풀리비가 증가할 경우 감소하였다. 직선형 블레이드와 비틀린 블레이드의 효율은 풀리비 0.45 지점에서 52 %인 반면 소형 비틀린 블레이드의 효율은 풀리비 0.21 지점에서 54 %이다. 와류수차의 최대 발전량은 풀리비 0.5 지점 내에서 발생했다. 와류수차의 효율은 풀리비에 따라 0.2 ~ 58 % 범위에서 관찰되었다.

• 한국태양에너지학회 논문집
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• 제30권5호
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• pp.38-43
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• 2010

Enhancement of exterior's insulation performance like wall or window etc. is general way for building's energy efficient and thermal performance. But exterior's opening plan is important for minimizing the energy consumption and heat loss. In this paper, energy saving rate will be analyzed and compared considering the window area's rate and window's SC(Shading Coefficient) in a apartment with Building Energy Efficiency Rating System's evaluation tool. In the process of evaluation, energy saving rate is measured at each stage of the window area's rate from 20% to 60% every 10% term and the shading coefficient value from 1.0 to 0.6. As a result of this research, energy saving evaluation could not be measured exactly with existing evaluation tool. Accord this research, Building Energy Rating System's evaluation range is needed to be broaden for exact evaluation of energy saving rate.