• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1177-1181
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• 2009

Heat loss from a convective rectangular profile annular fin with variable inside fluid heat transfer coefficient and fin height is calculated by using both the one dimensional analytic method and two dimensional variables separation method. Heat loss from the two dimensional method and the relative error of heat loss between the one dimensional method and two dimensional method are presented as a function of the fin length, ambient convection characteristic number and fin height. One of the results shows that the relative error of heat loss between one dimensional method and two dimensional method is within 0.7% in the range of given parameters in this study.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.2
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• pp.689-696
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• 1996

A comparison is made of the heat loss from a hollow cylinder, computed using an one-dimensional analytic method and a two-dimensional separation of variables scheme. For a two-dimensional analysis, the temperature of the inner surface as a boundary condition can be varied along the length of the cylinder by varing the temperature variation factor, b. Comparisons of the heat loss from the hollow cylinder using these two methods are given as a function of non-dimensional cylinder length, the ratio of the outer radius to the inner radius, temperature variation factor and Biot number. The result shows that the value of the heat loss from the hollow cylinder obtained using the one-dimensional analytic method becomes close to the value given by the two-dimensional separation of variables scheme as the value of Biot number and the non-dimensional hollow cylinder length increase and as the ratio of the outer radius to the inner radius decreases.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1992.11a
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• pp.13-18
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• 1992

대형 틸팅패드 저어널베어링은 고속안정성 특성이 우수한 베어링으로서 시스템의 안정성이 매우 중요시되는 터빈발전기 등 대형 고속 회전기계에 많이 사용되고 있다. 그런데 이들 대형 저어널베어링에서는 유막의 온도상승이 매우 많고, 유체의 흐름이 거의 난류영역에 이르기 때문에 베어링의 운전특성을 정확하게 예측하기가 어려운 실정이다. Hopf & Schuler는 대형 틸팅패드 저어널베어링에 대한 실험적 연구에서 유동상태에 따라 베어링의 온도분포가 서로 달라진다고 발표하였다. 대형 틸팅패드 저어널베어링은 구조적으로 유동상태가 복잡할 뿐만 아니라 계산과정도 까다로운 편이어서 온도상승과 난류를 고려하여 엄밀하게 운전특성을 예측한 연구는 거의 없다. 따라서 본 연구에서는 대형 틸팅패드 저어널베어리으이 운전특성을 보다 엄밀하게 예측하기 위하여 3차원 적으로 유막의 점도변화 및 패드에서의 열전달을 고려하고, 와점성계수를 이용한 난류윤활이론을 사용하여 유막의 온도상승 및 난류가 베어링의 온도분포, 부하능력, 마찰손실 등의 운전특성에 미치는 영햐을 보다 엄밀하게 제시하고자 한다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.9
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• pp.855-862
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• 2005

An experimental investigation has been carried out for aluminum foam heat sink inserted into the annulus to examine the feasibility as a heat sink for high performance forced water cooling in the annulus. The local wall temperature distribution, inlet and outlet pressures and temperatures, and heat transfer coefficients were measured for heat flux of 13.6, 18.9, 25.1, 31.4 $kw/m^2$ and Reynolds number ranged from 120 to 2000. Experimental results show that the friction factor is higher than clear annulus without aluminum foam, while the significant augmentation in Nu is obtained. This technique can be used for the compactness of the heat exchanger.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.3
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• pp.52-59
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• 2001

In this study, a technique has been developed to analyze the performance of the launching system using a gas generator of solid propellant. The physical model which described the thermodynamic behaviors of all launching devices from gas generator to canister and the dynamic behavior of missile was established, applying the empirical coefficients in the heat loss model. The processes of combustion, flow, and heat transfer inside the chamber of gas generator and the launching system were simulated by numerical method. The theoretical analysis guided the optimal design of gas generator and system, which made the launching system satisfy the requirements of good performance and high reliability.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.2
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• pp.215-223
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• 1999

Evaporation heat transfer coefficient and pressure loss were measured for three different micro-fin tubes and a smooth tube. The experiments were carried out with R-22 over a wide range of vapor Quality, mass velocity and heat flux. Heat transfer coefficient of the tube with slightly modified fin shape was found to be higher than that of the commercial reference tube by 60%. The improvement of heat transfer has been achieved without noticeable increase of pressure loss. Heat transfer coefficient was increased with increasing quality, refrigerant mass flux, and heat flux. However, the effect of refrigerant mass flux and heat flux was not great. Heat transfer coefficient at bottom was lower than that at top of the tube in low quality region, which suggested the existence of stratification in the micro-fin tube. Pressure drop was linearly increased with increasing refrigerant quality and was proportional to about square of mass flux.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.04a
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• pp.35-35
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• 1998

고체 로켓 추진기관의 노즐을 개발하기 위해서는 주어진 체계 제한 조건내에서 기본적인 가스의 동력학, 내탄도에 의한 형상 설계, 재료 개발 및 적용 기술, 열전달 계산에 의한 열설계 및 해석 등이 종합적으로 적용되며 수많은 반복과정을 거쳐야 한다. 특히 최근에는 알루미늄 함유량을 증가시켜 연소가스의 온도가 300$0^{\circ}C$ 이상이 되는 고성능 추진제가 일반적으로 적용되고 있으므로 고온에 의한 열적문제가 심각하게 대두되고 있으며 이에 견디는 신뢰도가 높은 노즐 설계개발이 요구되고 있다. 노즐목을 노즐내에서 열부하가 가장 심한 곳으로 노즐목 확대에 의한 추력 손실을 최소화하기 위해 내삭마성이 강한 재료를 선정하여야 하며, 그래파이트는 이러한 조건을 만족시키는 소재의 하나로 많이 적용되고 있다.

• Journal of the Korean Solar Energy Society
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• v.24 no.1
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• pp.29-38
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• 2004

자동자 공조용 시스템에 사용되는 평행류형 응축기에 대하여 실제 운전조건에서 성능을 예측할 수 있는 모델링을 개발하였다. 모델링에 사용된 방법은 유효도-전달단위수법이고, 국소구간을 나누어 해석하는 국소구간법을 사용하였다. 모델링에 사용된 작동유체는 HFC134a이며, 응축기를 흐르면서 방생하는 냉매의 압력손실에 대한 물성변화를 포함시켜 보다 실제에 가깝게 해석하였다. 모델링에는 공기측과 냉매측의 열전달계수와 압력손실계수에 관한 상관식들을 포함하고 있다. 모델링의 결과는 실험값과 비교하여 비교적 잘 일치한다.

• Tunnel and Underground Space
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• v.23 no.3
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• pp.241-259
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• 2013

A packed bed thermal energy storage (TES) consisting of solid storage medium of rock or concrete through which the heat transfer fluid is circulated is considered as an attractive alternative for high temperature sensible heat storage, because of the economical viability and chemical stability of storage medium and the simplicity of operation. This study introduces the technologies of packed bed thermal energy storage, and presents a numerical model to analyze the thermal energy balance and the performance efficiency of the storage system. In this model, one dimensional transient heat transfer problem in the storage tank is solved using finite difference method, and temperature distribution in a storage tank and thermal energy loss from the tank wall can be calculated during the repeated thermal charging and discharging modes. In this study, a high temperature thermal energy storage connected with AA-CAES (advanced adiabatic compressed air energy storage) was modeled and analyzed for the temperature and the energy balance in the storage tank. Rock cavern type TES and above-ground type TES were both simulated and their results were compared in terms of the discharging efficiency and heat loss ratio.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.4
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• pp.313-327
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• 2008

Thermo-mechanical coupled behavior of an underground structure during a fire accident have not been fully understood yet. Moreover, when such a thermo-mechanical coupled behavior is not considered in numerical analyses based on conventional heat transfer theory, fire-induced damage zone in an underground structure can be considerably underestimated. This study aims to develop a FEM-based numerical technique to simulate the thermo-mechanical coupled behavior of an underground structure in a fire accident. Especially, an element elimination model is newly proposed to simulate fire-induced structural loss together with a convective boundary condition. In the proposed model, an element where the maximum temperature calculated from heat transfer analysis is over a prescribed critical temperature is eliminated. Then, the proposed numerical technique is verified by comparing numerical results with experimental results from real fire model tests. From a series of parametric studies, the key parameters such as critical temperature, element size and temperature-dependent convection coefficients are optimized for the RABT and the RWS fire scenarios.