• 설비공학논문집
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• 제13권6호
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• pp.431-439
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• 2001

Recently, multi-room type heat pump system has aroused much attention, because it can achieve much reduction of installation cost and space as well as energy saving in companion with the single room type heat pump system. In the present study, performance characteristics of a 3 room type inverter driven heat pump system, which is widely spread in Japanese market, are measured.. In the single room operation, performances of a heat pump system such s the difference of compressor outlet and inlet pressures and the mass flowrate may increase with the increase of cooling capacity so that COP of the system decrease with the increase of cooling capacity. However, in the 2 room operation, mass flowrate and COP of the total system increase markedly as compared with the single room operation.

• Computers and Concrete
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• 제24권6호
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• pp.541-553
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• 2019

Alkali-silica reaction (ASR) in concrete can induce degradation in its mechanical properties, leading to compromised serviceability and even loss in load capacity of concrete structures. Compared to other properties, ASR often affects the modulus of elasticity more significantly. Several empirical models have thus been established to estimate elastic modulus reduction based on the ASR expansion only for condition assessment and capacity evaluation of the distressed structures. However, it has been observed from experimental studies in the literature that for any given level of ASR expansion, there are significant variations on the measured modulus of elasticity. In fact, many other factors, such as cement content, reactive aggregate type, exposure condition, additional alkali and concrete strength, have been commonly known in contribution to changes of concrete elastic modulus due to ASR. In this study, an artificial intelligent model using artificial neural network (ANN) is proposed for the first time to provide an innovative approach for evaluation of the elastic modulus of ASR-affected concrete, which is able to take into account contribution of several influence factors. By intelligently fusing multiple information, the proposed ANN model can provide an accurate estimation of the modulus of elasticity, which shows a significant improvement from empirical based models used in current practice. The results also indicate that expansion due to ASR is not the only factor contributing to the stiffness change, and various factors have to be included during the evaluation.

• 한국환경과학회지
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• 제15권9호
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• pp.819-827
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• 2006

We study on the dynamic interaction with a simulated physical-biological coupled model response to nutrient reduction scenario in Jinhae Bay. According to the low relative errors, high regression coefficients of COD and DIN, and realistic distribution in comparison to the observation, our coupled model could be applicable for assessing the marine ecosystem response to nutrient input reduction in Jinhae Bay. Due to the new construction and expansion of sewage treatment plant from our government, we reduce 50% nutrient inputs near Masan Bay and sewage treatment plant. COD achieves Level II in Korea standard of the water quality from the middle of the Masan Bay to all around Jinhae Bay except the inner Masan Bay remaining at Level III. When our experiment reduces 50% nutrient inputs near Masan Bay and Dukdong sewage treatment plant simultaneously, COD decreases to about 0.1-1.2 mg/L $(128^{\circ}30'{\sim}128^{\circ}40'\;E,\;35^{\circ}05'{\sim}35^{\circ}11'\;N)$. The COD from the middle of the Masan Bay to Jinhae Bay achieves Level II.

• 공업화학
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• 제26권1호
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• pp.80-85
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• 2015

본 연구에서는 리튬이차전지의 음극활물질인 실리콘/탄소 복합소재를 제조하여 전기화학적 특성을 확인하였다. 실리콘/탄소 합성물은 마그네슘의 열 환원 반응을 통해 SBA-15 (Santa Barbara Amorphous material No. 15)를 제조한 후 페놀 수지의 탄화 과정을 통해 합성하였다. 실리콘/탄소를 음극으로 제조하여 충방전, 사이클, 순환전압전류, 임피던스 테스트를 통해 분석하였다. 실리콘에 코팅된 탄소는 전기 전도도를 향상시켜 Rct값을 235 ohm (silicon)에서 30 ohm (실리콘/탄소)으로 낮추었고 리튬의 탈 삽입 시에 발생하는 실리콘의 팽창을 억제하여 전극을 안정화시키는 효과를 보여주었다. 실리콘/탄소 전극을 사용한 리튬이차전지는 1,348 mAh/g의 용량을 나타내었고 50사이클 동안 76%의 안정성을 보여주었다.

• Current Photovoltaic Research
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• 제8권3호
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• pp.86-93
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• 2020

The investment in solar and wind generation is rapidly increasing with government's renewable expansion policy and Renewable Portfolio Standard (RPS). Since the large penetration of solar and wind generation increases the variability and uncertainty of supply and demand balance in power system, the government is pursuing the policy of supplying energy storage system (ESS) linked to renewable energy. ESS contributes to the ease of transmission and distribution grid by shifting PV generation from daytime to evening hours. Recently, the declining market price of REC as ESS incentive, policies to cut down incentives and limited ESS storage due to fire events lead to the aggravation of long-term profitability, thus working as a barrier of ESS spreading. In this study, the factors affecting the profit of ESS are analyzed and brief indicators are derived. Based on the indicators, the profit changes are analyzed considering the variation of REC market price and REC incentive weights. Based on the profit change with respect to the increase of ESS capacity, economical ESS installation capacity is suggested.

• Journal of Forest and Environmental Science
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• 제32권2호
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• pp.173-181
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• 2016

This study designed a model of the efficient production schemes and raw materials transportation optimization of current South Korean's simple and monolithic distribution system of wood to build a SCM (supply chain management) as a basic level to establish a distribution of future by pellet production of raw materials costs and reduce transport costs, and specifically to forest of pallet to contribute to revitalizing the market. The result of each transportation costs after building the best transportation network from raw material supply area to demand area applying transport law was 964,600 thousands Won from 6 supply areas to 7 demand areas. And the result of each model's analysis to get the pellet's efficient production through production cost reduction showed that it reduced from 325,701 Won/t to 240,106 Won/t, results of existing efficient pellet for the production model 8,233 tons over 20,000 tons annual production capacity from the size of the expanded production capacity when the expansion. However, when the production size expanded to 50,000 Tons of the production, the effect was very small even though production cost decreased.

• Journal of Electrical Engineering and Technology
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• 제9권6호
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• pp.2042-2048
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• 2014

In medium voltage electrical distribution networks, reforming the loss reduction is important, and in line with this, the issue of system engineering and use of proper equipment Expansion of distribution systems results in higher system losses and poor voltage regulation. Therefore, an efficient and effective distribution system has become more important. So, proper selection of conductors in the distribution system is crucial as it determines the current density and the resistance of the line. Evaluation of aging conductors for losses and costs imposed in addition to the careful planning of technical and economic networks can be identified in the network design. In this paper the use of imperialist competitive algorithm; genetic algorithm; is proposed to optimal branch conductor selection and reconstruction in radial distribution systems planning. The objective is to minimize the overall cost of annual energy losses and depreciation on the cost of conductors to improve productivity given the maximum current carrying capacity and acceptable voltage levels. Simulations are carried out on 69-bus radial distribution network using genetic algorithm approaches to show the accuracy as well as the efficiency of the proposed solution technique.

• 설비공학논문집
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• 제23권7호
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• pp.505-512
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• 2011

Recently, many researchers have analyzed the performance of the transcritical $CO_2$ refrigeration cycle in order to identify opportunities to improve the system energy efficiency. The reduction of the expansion process losses is one of the key issues to improve the efficiency of the transcritical $CO_2$ refrigeration cycle. In this study, the analytical study on the performance characteristics of $CO_2$ cycle with an ejector carried out with a variation of outdoor temperature, gascooler inlet air velocity, evaporator inlet air velocity, and evaporator inlet air temperature. As a result, the system performance could be improved over 85% by using an ejector for various operating condition because of the reduction of compressor work. Moreover, the cooling capacity increased about 18% for variable outdoor condition. Therefore, the high performance of an ejector system could be maintained for wide operating conditions and system reliability could be improved compared to that of a basic system.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.431-436
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• 2002

In this paper, to seek a solution of reducing autogenous shrinkage three types of bar restricted concrete specimens which have similar compressive strength were tested. The three type of concrete were plain concrete-P25 type, $10^{\circ}C$ fly-ash replaced concrete-F10 type, and $1^{\circ}C$ expansion admixture replaced concrete-SP1 type, and with the test result an experimental study was conducted to gain the tensile stress of concrete. From the result of P25, SP1, F10 tests, it was found that by the age of 14 the ratios of tensile stress to tensile strength of three specimens are $75^{\circ}C$, $47^{\circ}C$, $52^{\circ}C$ respectively. so we came to a conclusion that the SP1-type concrete has better capacity to reduce autogenous shrinkage than F10-type concrete at similar compressive strength condition.

• 한국자동차공학회논문집
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• 제6권2호
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• pp.203-211
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• 1998

The system performance of an automobile air conditioning system with variations of charging conditions has been investigated experimentally. An automobile air conditioning system was composed of laminated type evaporator, parallel flow type condenser, swash plate type com-pressor, externally equalized thermostatic expansion valve and receiver drier. The objective of this study was to quantify the influence of the refrigerant charge under the steady state operation of an automobile air conditioning system. The results indicated that a 10% undercharge caused a 10% reduction in the capacity of evaporator.