• 제목/요약/키워드: ground thermal conductivity

검색결과 160건 처리시간 0.034초

지중 열전도도 측정을 위한 광섬유 센서의 건전성 (Integrity of Optical Fiber Sensor for Measurement of Ground Thermal Conductivity)

  • 윤석;최정찬;이승래;리 마이클 명섭
    • 한국전산구조공학회:학술대회논문집
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    • 한국전산구조공학회 2011년도 정기 학술대회
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    • pp.157-160
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    • 2011
  • 본 연구에서는 광섬유 센서 기반 스마트 모니터링 시스템이 지중 열전도도 측정에도 효율적으로 적용될 수 있는지를 분석하였다. 이를 위해 광섬유 온도센서를 이용하여 지반의 열전도도를 측정할 수 있는 열응답 시험기가 개발되었다. 개발된 열응답 시험기는 기존의 RTD(Resistance Temperature Detector) 온도 센서 외에 광섬유 센서의 한 종류인 FBG(Fiber Bragg Grating) 센서도 실시간적으로 측정할 수 있는 시스템으로 구성되어 있다. 개발된 장비의 적용성 검증을 위하여 주문진 표준사를 이용하여 모형토조 내에 일정한 간극비에 맞추어 시료가 조성되었으며 지중열교환기는 U자형 파이프가 사용되었다. 20시간동안 열응답 시험을 통하여 광섬유 센서와 RTD 센서를 동시에 이용하여 온도값을 측정하여 표준사의 열전도도 값을 산출하였다. 그 결과 모형실험을 통한 열전도도 값은 탐침법을 통해 얻어진 열전도도 값과 선형 열원 모델(line source model) 해석해와 거의 유사하게 나타났으며 광섬유 센서와 RTD 센서와의 온도차는 0.1~0.3$^{\circ}$로써 유사한 값을 나타내었다. 따라서 본 연구에서 개발된 광섬유 기반 열응답 시험기는 지반의 열전도도를 측정하는데 효과적으로 사용될 수 있음을 알 수 있었으며 향후 지열시스템 가동에 따른 지중열 교환기의 손상도 평가 및 경보시스템 개발을 위해 지중열교환기의 거동을 실시간으로 모니터링 하는데 있어서도 효과적으로 사용될 수 있을 것으로 생각된다.

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Study on the Recycling of Nuclear Graphite after Micro-Oxidation

  • Liu, Juan;Wang, Chen;Dong, Limin;Liang, Tongxiang
    • Nuclear Engineering and Technology
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    • 제48권1호
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    • pp.182-188
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    • 2016
  • In this paper, a feasible strategy for the recycling of nuclear graphite is reported, based on the formation mechanism and the removal of carbon-14 by micro-oxidation. We investigated whether ground micro-oxidation graphite could be used as a filler to make new recycled graphite and which graphite/pitch coke ratio will give the recycled graphite outstanding properties (e.g., apparent density, flexural strength, compressive strength, and tensile strength). According to the existing properties of nuclear graphite, the ratio of graphite to pitch coke should not exceed 3. The recycled reactor graphite has been proven superior in density, strength, and thermal conductivity. The micro-oxidation process enhances the strength of the recycled graphite because there are more pores and unsmooth surfaces on the oxidized graphite particles, which is beneficial for the access of the pitch binder and leads to efficient joint adhesion among the graphite particles.

개방형 지열시스템의 효율적 설계를 위한 영향인자에 대한 연구 (A Study on Significant Parameters for Efficient Design of Open-loop Groundwater Heat Pump (GWHP) Systems)

  • 박병학;전원탁;이보현;이강근
    • 한국지하수토양환경학회지:지하수토양환경
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    • 제20권4호
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    • pp.41-50
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    • 2015
  • Open-loop groundwater heat pump (GWHP) system generally has benefits such as a higher coefficient of performance (COP), lower initial cost, and flexible system size. The hydrogeological conditions in Korea have the potential to facilitate the use of the GWHP system because a large number of monitoring wells show stable groundwater temperatures, shallow water levels, and high well yields. However, few studies have been performed in Korea regarding the GWHP system and the most studies among them dealt with Standing Column Well (SCW). Because the properties of the aquifer have an influence on designing open-loop systems, it is necessary to perform studies on various hydrogeological settings. In this study, the hydrogeological and thermal properties were estimated through various tests in the riverside alluvial layer where a GWHP system was installed. Under different groundwater flow velocities and pumping and injection rates, a sensitivity analysis was performed to evaluate the effect of such properties on the design of open-loop systems. The results showed that hydraulic conductivity and thermal dispersivity of the aquifer are the most sensitive parameters in terms of performance and environmental aspects, and sensitivities of the properties depend on conditions.

Influence of fly ash and GGBFS on the pH value of cement mortar in different curing conditions

  • Shafigh, Payam;Yousuf, Sumra;Ibrahim, Zainah;Alsubari, Belal;Asadi, Iman
    • Advances in concrete construction
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    • 제11권5호
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    • pp.419-428
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    • 2021
  • The pH of cement-based materials (CBMs) is an important factor for their durability, sustainability, and long service life. Currently, the use of supplementary cementitious materials (SCMs) is becoming mandatory due to economic, environmental, and sustainable issues. There is a decreasing trend in pH of CBMs due to incorporation of SCMs. The determination of numerical values of pH is very important for various low and high volume SCMs blended cement mortars for the better understanding of different defects and durability issues during their service life. In addition, the effect of cement hydration and pozzolanic reaction of SCMs on the pH should be determined at initial and later ages. In this study, the effect of low and high-volume fly ash (FA) and ground granulated ballast furnace slag (GGBFS) cement mortars in different curing conditions on their pH values has been determined. Thermal gravimetric analysis (TGA) was carried out to support the findings from pH measurements. In addition, thermal conductivity (k-value) and strength activity indices of these cement mortars were discussed. The results showed that pH values of all blended cement mortars were less than ordinary Portland cement (OPC) mortar in all curing conditions used. There was a decreasing tendency in pH of all mortars with passage of time. In addition, the pH of cement mortars was not only dependent on the quantity of Ca(OH)2. The effect of adding SCMs on the pH value of cement mortar should be monitored and measured for both short and long terms.

단열공법이 적용된 겨울철 도로터널의 동결저감 효과 분석 (Analysis on Freezing Reduction of Road Tunnels with Heat Insulation Method during Winter)

  • 손희수;전경재;윤찬영
    • 한국지반공학회논문집
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    • 제33권8호
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    • pp.17-27
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    • 2017
  • 우리나라 북동부에 위치하고 있는 강원지역은 겨울철 일 평균온도가 영상권을 유지하는 타 지역들과는 달리 일평균온도가 영하로 떨어지는 가장 추운 지역이다. 이에따라 지속적으로 도로터널의 라이닝부에 대한 동결피해 발생 사례가 보고되고 있으나 동결피해 저감을 위한 단열설계 기준 및 관련 연구는 아직까지 매우 부족하다. 본 연구에서는 단열공법 적용에 따른 도로터널의 동결저감 효과를 분석하기 위하여 겨울철 강원지역 도로터널의 지반특성과 기후특성을 고려한 해석적 연구를 수행하였다. 그 결과, 라이닝부의 콘크리트와 숏크리트 두께의 차이는 동결심도에 큰 영향을 미치지 않는 것으로 나타났으나 단열재의 적용 시에는 동결심도가 크게 감소하는 것으로 나타났다. 또한 배면지반의 열전도율과 외기온도 지속지간의 변화에 따라서 동결심도가 큰 영향을 받으므로 이러한 영향을 고려하여 단열재의 두께를 산정하여 적용한다면 우수한 동결저감 효과를 보일 것으로 판단된다.

설비공학 분야의 최근 연구 동향 : 2013년 학회지 논문에 대한 종합적 고찰 (Recent Progress in Air-Conditioning and Refrigeration Research : A Review of Papers Published in the Korean Journal of Air-Conditioning and Refrigeration Engineering in 2013)

  • 이대영;김사량;김현정;김동선;박준석;임병찬
    • 설비공학논문집
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    • 제26권12호
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    • pp.605-619
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    • 2014
  • This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2013. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) The research works on the thermal and fluid engineering have been reviewed as groups of fluid machinery, pipes and relative parts including orifices, dampers and ducts, fuel cells and power plants, cooling and air-conditioning, heat and mass transfer, two phase flow, and the flow around buildings and structures. Research issues dealing with home appliances, flows around buildings, nuclear power plant, and manufacturing processes are newly added in thermal and fluid engineering research area. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics, pool boiling and condensing heat transfer and industrial heat exchangers. Researches on heat transfer characteristics included the results for general analytical model for desiccant wheels, the effects of water absorption on the thermal conductivity of insulation materials, thermal properties of Octadecane/xGnP shape-stabilized phase change materials and $CO_2$ and $CO_2$-Hydrate mixture, effect of ground source heat pump system, the heat flux meter location for the performance test of a refrigerator vacuum insulation panel, a parallel flow evaporator for a heat pump dryer, the condensation risk assessment of vacuum multi-layer glass and triple glass, optimization of a forced convection type PCM refrigeration module, surface temperature sensor using fluorescent nanoporous thin film. In the area of pool boiling and condensing heat transfer, researches on ammonia inside horizontal smooth small tube, R1234yf on various enhanced surfaces, HFC32/HFC152a on a plain surface, spray cooling up to critical heat flux on a low-fin enhanced surface were actively carried out. In the area of industrial heat exchangers, researches on a fin tube type adsorber, the mass-transfer kinetics of a fin-tube-type adsorption bed, fin-and-tube heat exchangers having sine wave fins and oval tubes, louvered fin heat exchanger were performed. (3) In the field of refrigeration, studies are categorized into three groups namely refrigeration cycle, refrigerant and modeling and control. In the category of refrigeration cycle, studies were focused on the enhancement or optimization of experimental or commercial systems including a R410a VRF(Various Refrigerant Flow) heat pump, a R134a 2-stage screw heat pump and a R134a double-heat source automotive air-conditioner system. In the category of refrigerant, studies were carried out for the application of alternative refrigerants or refrigeration technologies including $CO_2$ water heaters, a R1234yf automotive air-conditioner, a R436b water cooler and a thermoelectric refrigerator. In the category of modeling and control, theoretical and experimental studies were carried out to predict the performance of various thermal and control systems including the long-term energy analysis of a geo-thermal heat pump system coupled to cast-in-place energy piles, the dynamic simulation of a water heater-coupled hybrid heat pump and the numerical simulation of an integral optimum regulating controller for a system heat pump. (4) In building mechanical system research fields, twenty one studies were conducted to achieve effective design of the mechanical systems, and also to maximize the energy efficiency of buildings. The topics of the studies included heating and cooling, HVAC system, ventilation, and renewable energies in the buildings. Proposed designs, performance tests using numerical methods and experiments provide useful information and key data which can improve the energy efficiency of the buildings. (5) The field of architectural environment is mostly focused on indoor environment and building energy. The main researches of indoor environment are related to infiltration, ventilation, leak flow and airtightness performance in residential building. The subjects of building energy are worked on energy saving, operation method and optimum operation of building energy systems. The remained studies are related to the special facility such as cleanroom, internet data center and biosafety laboratory. water supply and drain system, defining standard input variables of BIM (Building Information Modeling) for facility management system, estimating capability and providing operation guidelines of subway station as shelter for refuge and evaluation of pollutant emissions from furniture-like products.

압축 벤토나이트 완충재의 비열 추정 (A Prediction of Specific Heat Capacity for Compacted Bentonite Buffer)

  • 윤석;김건영;백민훈
    • 방사성폐기물학회지
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    • 제15권3호
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    • pp.199-206
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    • 2017
  • 고준위폐기물을 처분하기 위한 심층 처분시설은 지하 500~1,000 m 깊이의 암반층에 설치된다. 심층 처분시스템의 구성 요소로는 처분용기, 완충재, 뒷채움 및 근계 암반이 있다. 이 중 완충재는 심층 처분시스템에 있어 필수적인 요소인데, 완충재는 지하수 유입으로부터 처분용기를 보호하고, 방사성 핵종 유출을 저지한다. 처분용기에서 발생하는 고온의 열량은 완충재로 전파되기에 완충재의 열물성은 처분시스템의 안정성 평가에 상당히 중요하다고 할 수 있다. 완충재의 열전도도 규명에 대한 연구는 많이 진행되고 있는 반면, 비열에 대한 연구는 미진한 상태이다. 따라서 본 연구에서는 국내 경주산 압축 벤토나이트 완충재(KJ-II)에 대한 비열 추정 모델을 개발하고자 하였다. 압축 벤토나이트 완충재의 비열은 이중 탐침법을 이용하여 다양한 포화도와 건조밀도에 따라 측정하였으며, 총 33개의 실험 데이터를 토대로 회귀분석을 이용하여 경주 압축 벤토나이트의 비열을 추정할 수 있는 모델을 제시하였다.

심층 처분 시설의 수리 역학적 해석을 통한 벤토나이트 버퍼의 역학적 영향 인자 중요도 평가 (A Coupled Hydro-Mechanical Analysis of a Deep Geological Repository to Assess Importance of Mechanical Factors of Bentonite Buffer)

  • 전윤수;이승래;김민섭;전준서;김민준
    • 터널과지하공간
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    • 제29권6호
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    • pp.439-455
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    • 2019
  • 완충재는 심지층 고준위 방사성 폐기물 저장소의 주요 구성 요소이다. 벤토나이트는 높은 열전도율과 낮은 수리투과성의 특성으로 완충재의 핵심 구성 요소로 다수의 국가에서 채택되었다. 심층 처분은 지하수 유입을 일으키고 이는 완충재 및 뒷채움재의 팽윤압을 초래한다. 완충재에서 발생하는 고압의 팽윤압은 처분용기에 영향을 줄 수 있기에 정밀한 완충재의 팽윤압 예측은 안전한 처분 시스템 구축에 있어서 필수적이다. 따라서 본 연구에서는 MX-80 벤토나이트의 수리역학적 거동에 대한 팽윤압 예측 모델을 세우고, 그 결과를 토대로 민감도 분석을 시행하였다.

생물개스 발생시스템을 위한 지하매설콘크리트 다이제스터의 열전달에 관한 연구 (Study on the Heat Transfer Phenomenon around Underground Concrete Digesters for Bigas Production Systems)

  • 김윤기;고재균
    • 한국농공학회지
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    • 제22권1호
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    • pp.53-66
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    • 1980
  • The research work is concerned with the analytical and experimental studies on the heat transfer phenomenon around the underground concrete digester used for biogas production Systems. A mathematical and computational method was developed to estimate heat losses from underground cylindrical concrete digester used for biogas production systems. To test its feasibility and to evaluate thermal parameters of materials related, the method was applied to six physical model digesters. The cylindrical concrete digester was taken as a physical model, to which the model,atical model of heat balance can be applied. The mathematical model was transformed by means of finite element method and used to analyze temperature distribution with respect to several boundary conditions and design parameters. The design parameters of experimental digesters were selected as; three different sizes 40cm by 80cm, 80cm by 160cm and l00cm by 200cm in diameter and height; two different levels of insulation materials-plain concrete and vermiculite mixing in concrete; and two different types of installation-underground and half-exposed. In order to carry out a particular aim of this study, the liquid within the digester was substituted by water, and its temperature was controlled in five levels-35。 C, 30。 C, 25。 C, 20。C and 15。C; and the ambient air temperature and ground temperature were checked out of the system under natural winter climate conditions. The following results were drawn from the study. 1.The analytical method, by which the estimated values of temperature distribution around a cylindrical digester were obtained, was able to be generally accepted from the comparison of the estimated values with the measured. However, the difference between the estimated and measured temperature had a trend to be considerably increased when the ambient temperature was relatively low. This was mainly related variations of input parameters including the thermal conductivity of soil, applied to the numerical analysis. Consequently, the improvement of these input data for the simulated operation of the numerical analysis is expected as an approach to obtain better refined estimation. 2.The difference between estimated and measured heat losses was shown to have the similar trend to that of temperature distribution discussed above. 3.It was found that a map of isothermal lines drawn from the estimated temperature distribution was very useful for a general observation of the direction and rate of heat transfer within the boundary. From this analysis, it was interpreted that most of heat losses is passed through the triangular section bounded within 45 degrees toward the wall at the bottom edge of the digesten Therefore, any effective insulation should be considered within this region. 4.It was verified by experiment that heat loss per unit volume of liquid was reduced as the size of the digester became larger For instance, at the liquid temperature of 35˚ C, the heat loss per unit volume from the 0. 1m$^3$ digester was 1, 050 Kcal/hr m$^3$, while at for 1. 57m$^3$ digester was 150 Kcal/hr m$^3$. 5.In the light of insulation, the vermiculite concrete was consistently shown to be superior to the plain concrete. At the liquid temperature ranging from 15。 C to 350 C, the reduction of heat loss was ranged from 5% to 25% for the half-exposed digester, while from 10% to 28% for the fully underground digester. 6.In the comparison of heat loss between the half-exposed and underground digesters, the heat loss from the former was fr6m 1,6 to 2, 6 times as much as that from the latter. This leads to the evidence that the underground digester takes advantage of heat conservation during winter.

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온실내 근권부의 지중냉각부하 추정 (Estimation of Soil Cooling Load in the Root Zone of Greenhouses)

  • 남상운
    • 생물환경조절학회지
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    • 제11권4호
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    • pp.151-156
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    • 2002
  • 지중냉각이나 양액냉각과 같은 근권부 냉각은 뿌리의 활력 증진, 양수분 흡수력의 향상, 작물체온의 강하 및 고온스트레스의 감소 등에 효과가 있는 것으로 알려져 있으며, 또한 온실 전체를 냉방하는것 보다 경제적이다. 따라서 본 연구에서는 지중냉각시스템을 경제적인 고온극복 방법중의 하나로 생각하고, 기술을 체계화하기 위한 시도로 지중냉각시스템의 열전달 특성을 분석하여 냉각부하를 산정하기 위한 실험을 수행하였다. 지중열류 측정자료로부터 힘수비에 따른 토양의 열전도율을 분석하였으며, 함수비 19~36%의 범위에서 열전도율은 0.83~0.96W.m$^{-}$.$^{\circ}C$$^{-}$로 직선적인 증가를 보였다. 일사량, 지표온도 및 기온의 관측치로부터 일사량에 따른 지표온도 상승을 회귀분석한 결과 거의 직선적인 관계를 보였으며, 지표온도는 실내 수평면 일사량 300~800W.m$^{-2}$ 범위에서 작물이 없는 경우 3.5~7.$0^{\circ}C$,작물이 지표면을 거의 덮고 있는 경우 1.0~2.5$^{\circ}C$ 정도 기온보다 상승하는 것으로 나타났다. 실험자료를 이용하여 온실의 설계기온과 냉각설정 지온, 일사량 및 토양의 함수비에 따른 지중냉각시스템의 냉각부하를 구하였다. 실내일사량 300~600W.m$^{-2}$ , 토양함수비 20~40%의 범위에서 기온과 지온의 차이를 1$0^{\circ}C$로 유지하기 위해서는 46~59W.m$^{-2}$ 의 냉각열량이 필요한 것으로 나타났다. 보다 정확한 설계자료의 구축을 위해서는 다양한 조건별 실험을 추가로 수행해야 할 것으로 생각된다.EX>$\mu$$_{r}$′) and the dielectric loss ($\varepsilon$$_{r}$"/$\varepsilon$$_{r}$′) were increased. It was caused that the absorption characteristics of the absorber were improved. The conduction loss and magnetic loss were expected to be occurred together because two matching frequencies were shown with carbon addition. It was confirmed that the matching frequency of the microwave absorber could be controlled by controlling heat-treatment temperatures and carbon additions.ons.tions.加的)으로 되거나 과가황(過加黃)이 될 우려가 있는 제조공정(製造工程)에서는 흔히들 이 방법(方法)을 무시(無視)하고 있다. 여기서 강조(强調)해 두어야 할 것은 항상 제품(製品)의 외부(外部)를 완전(完全)히 가황(加黃)시킬 필요(必要)는 없다는 것이다. 다공성(多孔性)이나 기포생성(氣泡生成)을 조장(助長)하는 불량가황상태(不良加黃狀態)와 표면(表面)에서의 과가황상태간(過加黃狀態間)의 균형(均衡)을 취(取)해 줘야 하는데 물론(勿論) 이때는 가황시간(加黃時間)을 단축(短縮)시켜야 한다는 경제적(經濟的)인 측면(側面)도 아울러 고려(考慮)해야 한다. 이것은 고무기술자(技術者)가 당면(當面)해야할 과제(課題)