• Tunnel and Underground Space
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• v.21 no.4
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• pp.297-306
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• 2011

In this paper, we performed thermodynamic energy balance analysis of the underground lined rock cavern for compressed air energy storage (CAES) using the results of multi-phase heat flow analysis to simulate complex groundwater-compressed air flow around the cavern as well as heat transfer to concrete linings and surrounding rock mass. Our energy balance analysis demonstrated that the energy loss for a daily compression and decompression cycle predominantly depends on the energy loss by heat conduction to the concrete linings and surrounding rock mass for a sufficiently air-tight system with low permeability of the concrete linings. Overall energy efficiency of the underground lined rock caverns for CAES was sensitive to air injection temperature, and the energy loss by heat conduction can be minimized by keeping the air injection temperature closer to the ambient temperature of the surroundings. In such a case, almost all the heat loss during compression phase was gained back in a subsequent decompression phase. Meanwhile, the influence of heat conductivity of the concrete linings to energy efficiency was negligible.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2009.11a
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• pp.449-450
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• 2009

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.2
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• pp.55-60
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• 2014

The present study has been conducted to develope a heating system for a green house with heat from underground air at Jeju Island. The temperature of the air deposited in the underground is $16{\sim}18^{\circ}C$ throughout the year, and it also has a large amount of moisture. Therefore, the air could not directly used for the heating of a green house. In this study, a heat pump with dehumidification function has been developed, which consisted of three evaporators, where the moisture removal occurs, accompanied by temperature drop. The dropped temperature is recovered, while passing through a series condenser. The air temperature increased from $17^{\circ}C$ to 35 with a 2.1 kg/h of moisture removal rate. The developed system moisture removal performance shows 0.91 kg/kWh.

• Tunnel and Underground Space
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• v.21 no.5
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• pp.394-405
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• 2011

In this paper, we applied coupled non-isothermal, multiphase fluid flow and geomechanical numerical modeling using TOUGH-FLAC coupled analysis to study the complex thermodynamic and geomechanical performance of underground lined rock caverns (LRC) for compressed air energy storage (CAES). Mechanical stress in concrete linings as well as pressure and temperature within a storage cavern were examined during initial and long-term operation of the storage cavern for CAES. Our geomechanical analysis showed that effective stresses could decrease due to air penetration pressure, and tangential tensile stress could develop in the linings as a result of the air pressure exerted on the inner surface of the lining, which would result in tensile fracturing. According to the simulation in which the tensile tangential stresses resulted in radial cracks, increment of linings' permeability and air leakage though the linings, tensile fracturing occurred at the top and at the side wall of the cavern, and the permeability could increase to $5.0{\times}10^{-13}m^2$ from initially prescribed $10{\times}10^{-20}m^2$. However, this air leakage was minor (about 0.02% of the daily air injection rate) and did not significantly impact the overall storage pressure that was kept constant thanks to sufficiently air tight surrounding rocks, which supports the validity of the concrete-lined underground caverns for CAES.

• Tunnel and Underground Space
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• v.19 no.1
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• pp.11-18
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• 2009

Use of nuclear energy inevitably brings the problem of radioactive waste disposal. Repositories for disposing radioactive waste use underground space that is unconnected with the outside and the diagonal system, which allows the waste to be deposited. Ventilation if necessary because high-level radioactive waste generates heat. In this study, the air velocity through diagonal branches with regulators of different sizes and in different locations, was measured. The air velocity is determined by the size of the first and last regulators, regardless of the size of other regulators. In the diagonal system. Consequently, once the desired total airflow rate has been achieved by installing the appropriate first and last regulators, the other regulators fan be evenly installed to maintain the minimum air velocity needed.

• Tunnel and Underground Space
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• v.21 no.4
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• pp.287-296
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• 2011

We performed a numerical modeling study of thermodynamic and multiphase fluid flow processes associated with underground compressed air energy storage (CAES) in a lined rock cavern (LRC). We investigated air tightness performance by calculating air leakage rate of the underground storage cavern with concrete linings at a comparatively shallow depth of 100 m. Our air-mass balance analysis showed that the key parameter to assure the long-term air tightness of such a system was the permeability of both concrete linings and surrounding rock mass. It was noted that concrete linings with a permeability of less than $1.0{\times}10^{-18}\;m^2$ would result in an acceptable air leakage rate of less than 1% with the operational pressure range between 5 and 8 MPa. We also found that air leakage could be effectively prevented and the air tightness performance of underground lined rock cavern is enhanced if the concrete lining is kept at a higher moisture content.

• Tunnel and Underground Space
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• v.21 no.6
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• pp.518-525
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• 2011

In this study, the natural ventilation pressure resulting from the large altitude difference which is a characteristic of high radioactive waste repository and the caloric value of the heat emitted by wastes was calculated and based on the results, natural ventilation quantities were calculated. A high radioactive waste repository can be considered as being operated through closed cycle thermodynamic processes similar to those of thermal engines. The heat produced by the heating of high radioactive wastes in the underground repository is added to the surrounding air, and the air goes up through the upcast vertical shaft due to the added heat while working on its surroundings. Part of the heat added by the work done by the air can be temporarily changed into mechanical energy to promote the air flow. Therefore, if a sustained and powerful heat source exists in the repository, the heat source will naturally enable continued cyclic flows of air. Based on this assumption, the quantity of natural ventilation made during the disposal of high radioactive wastes in a deep geological layer was mathematically calculated and based on the results, natural ventilation pressure of $74{\sim}183$Pa made by the stack effect was identified along with the resultant natural ventilation quantity of $92.5{\sim}147.7m^3/s$. The result of an analysis by CFD was $82{\sim}143m^3/s$ which was very similar to the results obtained by the mathematical method.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.1
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• pp.29-39
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• 2017

In this research, thermal design data such as heat transfer coefficient on the wall surface required for ventilation system design which is to prevent the temperature rise in the underground utility tunnel that three sides are adjoined with the ground was investigated in numerical analalysis. The numerical model has been devised including the tunnel lining of the underground utility tunnel in order to take account for the heat transfer in the tunnel walls. The air temperature in the tunnel, wall temperature, and the heating value through the wall based on heating value(117~468 kW/km) of the power cable installed in the tunnel and the wind speed in the tunnel(0.5~4.0 m/s) were calculated by CFD simulation. In addition, the wall heat transfer coefficient was computed from the results analysis, and the limit distance used to keep the air temperature in the tunnel stable was examined through the research. The convective heat transfer coefficient at the wall surface shows unstable pattern at the inlet area. However, it converges to a constant value beyond approximately 100 meter. The tunnel wall heat transfer coefficient is $3.1{\sim}9.16W/m^2^{\circ}C$ depending on the wind speed, and following is the dimensionless number:$Nu=1.081Re^{0.4927}({\mu}/{\mu}_w)^{0.14}$. This study has suggested the prediction model of temperature in the tunnel based on the thermal resistance analysis technique, and it is appraised that deviation can be used in the range of 3% estimation.

• Tunnel and Underground Space
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• v.24 no.2
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• pp.166-175
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• 2014

In this study, the thermal environment in a large scale coal mine located in Taebaek, Gangwondo was assessed by a field survey. In order to estimate the thermal environment, various heat stress indices such as WBGT, HSI, ESI, KATA index and effective temperature were investigated. Correlation analysis was also conducted. It was found that the thermal environment in most workplace was high. In particular, the correlation coefficient between HSI reflected in physiological fatigue characteristic and the maximum sweat evaporation heat was -0.834. This shows that the correlation coefficient have the most influence on HSI index. The factor which has the most influence on the maximum sweat evaporation heat is velocity of air. The thermal environment of high-depth coal mines is likely to be improved by installing a structure that enables the maximum prevention of extended digging, air doors, or the leakage of the inflow of air in the first shaft.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.04a
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• pp.14-14
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• 1999

비활성 가스제너레이터는 가스터빈 추진기관 및 기타 열기관을 이용하여 연소가 되지 않는 저온의 공기를 생산하는 기계장치를 말하며 이러한 저온의 비활성 기체를 화재 지역에 분사하는 경우 기존의 소방수를 이용한 화재 진압방식보다 매우 효율적으로 화재진압에 사용되어 질 수 있다. 일반적으로 민항기 등의 가스터빈 추진 기관에서 배기되는 기체내에는 터빈입구온도(TIT : Turbine Inlet Temperature)및 초과공기지수(Excess Air Coefficient)에 따라 다르게 나타나지만 TIT가 1500$^{\circ}$K인 경우 약 13-14%정도의 산소가 잔존하는 것으로 알려져 있다. 따라서 본 연구에서는 가스터빈 및 열교환 시스템 그리고 터빈 1단 등의 시스템 조합율을 통하여 대기 중의 기체의 온도를 영하 2$0^{\circ}C$ 및 산소함유량을 약 5%수준까지 낮춤으로서 이를 대형 화재 진압에 사용하기 위한 연구이다. 비활성 가스제너레이터에 사용하는 연료로는 Kerosene 및 CNG(Compressed Natural Gas)등이 사용될 수 있으며, 유량이 8.1kg/sec인 터보축 가스터빈 엔진을 사용하는 경우 18750㎥ 부피의 비활성기체를 생산하는데 Kerosene 연료가 약 1톤(200＄ 이하)이 필요한 것으로 계산되며 이에 소요되는 시간도 약 52분에 지나지 않는 것으로 계산되었다. 만일 50kg/sec의 보다 큰 가스터빈 엔진을 사용하는 경우 약 9분 정도가 필요한 것으로 계산되었다. 사용되는 가스터빈은 압축비가 15, 열교환기의 효율이 $\varepsilon$=0. 그리고 최종 터빈 1단의 팽창비가 1.25가 적합한 것으로 계산된다. 연구 분석 결과 기술적 문제점으로는 배기 가스온도가 낮은데 따른 출구 부분의 Bearing, Sealing이 문제가 될 수 있다고 판단되며 배기 가스 자체에 대기 공기중에 함유되어 있던 습기가 얼어붙는(Icing화) 문제가 발생하기 때문에 배기가스의 Icing을 방지하기 위하여 압축기 끝단에서 공기를 추출하여 배기부분에 송출할 필요성이 있는 것으로 판단되었다. 출구가스의 기체 유동속도가 매우 빠르므로 (100-l10m.sec) 이를 완화하기 위한 디퓨저의 설계가 요구된다고 판단된다. 또 연소기 후방에 물을 주입하는 경우 열교환기 및 기타 부분품에 발생할 수 있는 부식 및 열교환 효율 저하도 간과할 수 없는 문제로 파악되었다. 이러한 기술적 문제가 적절히 해결되는 경우 비활성 가스 제너레이터는 민수용으로는 대형 빌딩, 산림, 유조선 등의 화재에 매우 적절히 사용되어 질 수 있을 뿐 아니라 군사적으로도 군사작전 중 및 공군 기지의 화재 그리고 지하벙커에 설치되어 있는 고급 첨단 군사 장비 등의 화재 뿐 아니라 대간첩작전 등에 효과적으로 활용될 수 있을 것으로 판단된다.