• 콘크리트학회논문집
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• 제11권3호
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• pp.101-111
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• 1999

Compared with the BF slag, the EAF slag has expansion due to the reaction with water and free CaO. Therefore it is specified in Concrete Specification that the FAP slag aggregated must not be used in concrete. Because of this reason it is unusual to use the EAF slag aggregate in concrete. The EAF slag aggregate treated with accelerated and water aging was comparatively satisfied with fundamental properties, which are specific gravity, unit weight, abrasion and immersion expansion ratio, as concrete aggregate. Therefore when we measured the compressive strength till 28 days, we found that the mortar and concrete replacing the natural aggregate with the EAF slag aggregate by 4 steps had better results than the concrete using the natural aggregate in a view of the compressive strength. But at 91 days, concrete using the EAF slag aggregate had no difference with it using the natural aggregate.

• 설비공학논문집
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• 제15권8호
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• pp.661-666
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• 2003

Constant area expansion devices such as capillary tubes, short tube orifices are being gradually replaced with electronic expansion valves (EEVs) because of increasing focus on comfort and energy conservation. In this study, the performance of a water-to-water heat pump as a function of refrigerant charge is investigated in steady state, cooling mode operation with expansion devices of a capillary tube and an EEV. The performance of the capillary tube system varies drastically according to the change of refrigerant charge amount and inlet temperature of the secondary fluid in the condenser. Cooling capacity and COP of the EEV system show little dependence on the refrigerant charge, while those are strongly dependent on the secondary fluid temperature at the condenser inlet. In general, for a wide range of operating conditions the EEV system shows much higher performance as compared with the capillary tube system. The performance of the EEV system can be optimized by adjusting EEV opening to maintain a constant superheat at all test conditions.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2010년도 춘계 학술대회 제22권1호
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• pp.275-276
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• 2010

본 연구에서는 MgO를 혼입한 콘크리트의 자기팽창 실험결과를 이용하여 물-결합재 비, MgO 첨가량, 양생온도 등의 영향인자를 고려한 자기팽창 모델을 제안하였으며, 모델 예측 결과가 실험 결과를 잘 일치하는 것을 확인하였다.

• 상하수도학회지
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• 제24권6호
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• pp.753-762
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• 2010

The objective of this study was to evaluate the backwashing frequency and method on the Granular Activated Carbon (GAC) in G WTP. A backwashing period was determined as 50 days and 60 days, respectively. Prior to Backwashing by head loss build, biomass concentration in effluent as constant and DO concentration was maintained more than 11.5 mg/L in GAC bed. Peak turbidity of backwashing water was 73.6~303 NTU. Mean turbidity of backwashing water at initial 9 minute of backwash operation was 50.7~82.8 NTU. After 30 minute backwashing operation, final turbidity reaches approximately 10 NTU. The frequency of backwashing and turbidity of backwashing water overtime were evaluated. At 20days of backwashing frequency, the peak turbidity was 73 NTU and 42 NTU respectively when 10% and 25% of expansion of GAC were applied. At 14 minute of backwashing time, it was observed that turbidity of 10% expansion of GAC was higher than that of 20% expansion.

• 한국세라믹학회지
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• 제26권5호
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• pp.698-704
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• 1989

Basic investigation for the flexural strength and water stability of hardened cement pastes using ordinary portland cement with water-soluble polyer (hydroxypropyl methyl cellulose ; HPMC) was carried out with 0.2 of water cement ratio. For molding of the specimen, the paste was mixed by twin roll mill. According to increase in the content of HPMC, the setting time of cement paste was delayed and the flexural strength was increased. The maximum flexural strength of hardened cement paste with 5.0wt% of HPMC was about 330 kg/$\textrm{cm}^2$. The expansion of the hardened cement paste immersed in water was increased with the content of water soluble polymer(HPMC). Consequently, the strength and the water stability of the hardened cement pastes were remarkably reduced by the expansion of them.

• 청정기술
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• 제14권4호
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• pp.248-255
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• 2008

초임계이산화탄소의 존재 하에서 세 가지 이온성액체(IL)의 부피팽창을 압력 32 MPa까지, 온도 313.15에서 333.15 K까지 뷰셀(view cell) 내에서 측정하였다. 이미다졸유도체 이온성액체인 육불화 1-부틸-3-메틸이미다졸([bmim][$PF_6$]), 사불화 1-부틸-3-메틸이미다졸([bmim][$BF_4$]), 사불화 1-옥틸-3-메틸이미다졸([omim][$BF_4$])을 연구에 사용하여, 압력, 온도, 양이온과 음이온의 성질, 그리고 수분 함량이 $CO_2$의 흡수에 의한 이온성액체의 부피팽창에 미치는 영향을 실험적으로 조사하였다. 부피팽창은 긴 양이온 알킬그룹을 가지고 있는 이온성액체 및 음이온 극성이 작은 이온성액체에서 크게 나타났다. 수분함량이 적을수록, 온도가 낮을수록, 그리고 압력이 높을수록 이온성액체상의 부피는 더 크게 나타났다.

• 한국산학기술학회논문지
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• 제13권9호
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• pp.4302-4309
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• 2012

지하구조물에 적절한 신축이음을 두지 않게 되면, 신축량에 대응하지 못해 구조물에 구조적 균열과 누수로 인한 콘크리트의 백태 등이 발생할 수 있다. 본 연구에서는 방수성능과 내구성이 우수한 새로운 지하구조물용 신축이음 장치에 대한 성능을 검증하였다. 유한요소해석을 통하여 지하구조물 신축이음장치의 간격을 설정하고 개발된 신축이음장치의 적정 신축량을 확인하였다. 또한, 검증실험결과 개발된 신축이음장치의 수축 신장에 따른 피로 기준을 만족하였으며 방수성능이 우수한 것으로 나타났다.

• Geomechanics and Engineering
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• 제25권4호
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• pp.283-294
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• 2021

This paper presents a rigorous solution for spherical cavity expansion in unsaturated soils under constant suction condition. The hydraulic behavior that describes the saturation-suction relationship is modeled by a void ratio-dependent soil-water characteristic curve, which allows the hydraulic behavior to fully couple with the mechanical behavior that is described by an extended critical state soil model for unsaturated soil through the specific volume. Considering the boundary condition and introducing an auxiliary coordinate, the problem is formulated to a system of first-order differential equations with three principal stress components and suction as basic unknowns, which is solved as an initial value problem. Parameter analyses are conducted to investigate the effects of suction and the overconsolidation ratio on the overall expansion responses, including the pressure-expansion response, the distribution of the stress components around the cavity, and the stress path of the soil during cavity expansion. The results reveal that the expansion pressures and the distribution of the stress components in unsaturated soils are generally higher than those in saturated soils due to the existence of suction.

• 설비공학논문집
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• 제14권1호
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• pp.10-20
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• 2002

A dynamic model of a water heater system heated by a heat pump was developed. The water heater system was composed of heat pump and hot water reservoirs. Finite volume method (FVM) was applied to describe the heat exchangers. A new constraint on electronic expansion valve (EEV) or thermostatic expansion valve (TXV) that can control superheat after the evaporator was developed. Dynamic performances were evaluated for various sizes of the reservoir. In order to compare those performances, time scale was normalized by time constant representing the characteristics of reservoir size. Time constant was determined from quasi steady-state simulation of the system. From the simulation, the size of the water heater reservoir was found to have a large influence on the transient performance of the sys- tem. Therefore, the optimization of the reservoir size is needed in a design process.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2009년도 학술발표회 초록집
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• pp.52-56
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• 2009

In this study a dynamic modeling scheme is presented to derive the probabilistic structure of soil water and plant water stress when subject to stochastic precipitation conditions. The newly developed model has the form of the Fokker-Planck equation, and its applicability as a model for the probabilistic evolution of the soil water and plant water stress is investigated under climate change scenarios. This model is based on the cumulant expansion theory, and has the advantage of providing the probabilistic solution in the form of probability distribution function (PDF), from which one can obtain the ensemble average behavior of the dynamics. The simulation result of soil water confirms that the proposed soil water model can properly reproduce the results obtained from observations, and it also proves that the soil water behaves with consistent cycle based on the precipitation pattern. The plant water stress simulation, also, shows two different PDF patterns according to the precipitation. Moreover, with all the simulation results with climate change scenarios, it can be concluded that the future soil water and plant water stress dynamics will differently behave with different climate change scenarios.