• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2002.02a
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• pp.151-157
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• 2002

화석에너지에 대한 경제적 부담과 환경오염문제를 줄이기 위하여 열펌프의 성능계수향상을 위하여 냉온 공기열교환기(HEEVA)를 고안하였고, 이 열교환기의 열특성과 성능계수향상에 미치는 영향을 분석하기 위하여 냉.난방 실험을 수행하였다. HEEVA에 의한 찬 공기와 더운 공기의 온도변화, 전열량 및 냉온 공기열교환기 효율, 총열전달계수등을 측정분석하였고, 냉난방시 외기온에 따른 열펌프의 성능계수, 소비전력, 응축기.증발기 출구 공기토출 온도 변화를 측정 분석함으로서 다음과 같은 결과를 얻을 수 있었다. 1. 외기온이 -4~11$^{\circ}C$로 변할 때 열펌프의 난방과정에서 HEEVA 찬공기 입출구 온도차는 4.5$^{\circ}C$에서 9.$0^{\circ}C$로 증가하였으며, HEEVA에 의한 영향으로 2~6$^{\circ}C$상승된 공기가 증발기 입구로 유입되어 냉매증발을 촉진하였다. 2. 실온이 4~22$^{\circ}C$일 때 HEEVA 더운공기 입출구 온도차는 3$^{\circ}C$에서 7$^{\circ}C$로 증가하였으며, 응축기에 유입되는 공기온도를 3~8$^{\circ}C$낮게 함으로서 압축기 소모전력을 감소시켜 COP 상승 효과를 나타냈다. 3. 외기온과 실온변화에 따라 풍량 346m$^3$/hr의 찬 공기가 받은 열량과 풍량 747m$^3$/hr의 더운 공기가 준 열량간의 차는 50~150kcal/hr로 나타났으며, 더운 공기가 준열량과 찬 공기가 받은 열량의 비가 83~98% 이었으므로 HEEVA의 열 교환율은 91% 을 보였다. 4. 총합열전달계수는 이론값이 실험 값보다 1~3W/m$^2$K 크게 나타났으며, 이 결과는 두 값 사이에 10% 내.외의 편차로서 Nusselt수를 구하기 위한 Petukhov상관식의 자체오차 15%에 비해 크지 않은 오차범주에 속하며, 이론상의 총합열전달계수 유도식의 타당성을 입증한 것이라 하겠다. 5. HEEVA를 작동함으로서 난방시 COP가 HEEVA를 작동하지 않았을 경우보다 0.3~0.5 향상된 것으로 나타났다. 이것은 HEEVA가 겨울철 난방에 효율을 높일수 있는 것으로 판단된다.

• Solar Energy
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• v.12 no.3
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• pp.28-36
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• 1992

The performance of a latent heat storage system using a thermosyphon as the heat transfer device between the heat source and the phase change material was investigated experimentally. In order to increase the effective conductivity of the phase change material, layers of copper wire mesh were immersed in the paraffin wax(Sunoco P-116) in such a way that they also may be considered as fins of the thermosyphon. The important results are as follows : (1) The void space of the wire mesh allowed the convection to occur, thus enhanced the performance of the system : (2) The increase of the number of layer of wire mesh increased the conduction heat transfer. However, it also had adverse effect of subduing convective motion of liquid wax : and (3) Overall heat transfer coefficient and thermosyphon conductance increased with the increase of the number of layer of wire mesh, whereas the heat transfer coefficient between the thermosyphon and the wax decreased.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.391-396
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• 1996

내부부수로, 벽면부수로, 모서리부수로를 포함하는 가압경수로형 원자로의 핵연료집합체를 모의하는 3$\times$3 봉다발을 모델로 수치해석을 통해 봉다발 주변의 유동특성을 알아보고 각 봉에서의 원주방향 위치에 따른 국소열전달 특성에 관해 고찰하였다. 봉다발에서 열전달계수의 분포는 벽면영향으로 인한 각 부수로에서의 유속분포와 밀접한 관계가 있으며 내부부수로에 인접한 봉에서 가장 높았고, 그 다음이 벽면부수로, 모서리부수로에 인접한 봉에서는 가장 작게 나타났다. 현재 핵연료의 열수력 설계시에 적용하고 있는 부수고 내의 모든 열수력학적 변수가 일정하다고 가정하는 부수로 해석방법은 봉다발내의 실제 열전달 현상과는 상당한 차이가 있음을 보여주었다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.04a
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• pp.29-29
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• 1998

고체 추진제 연소불안정에 관한 해석은 준-정상 1차원 해석인 QSHOD(Quasi-Steady Homogcneous One-Dimension)에 의하여 단순화된 지배방정식을 이용하여 응축영역을 해석하는 것이 일반적이다. 이때 외부교란에 대한 기체영역과 표면반응 영역의 응답은 화학반응이 발생하지 않는 고체영역의 응답에 비하여 매우 빠르므로 준-정상적인 거동을 한다. 본 연구에서는 복사열전달에 의한 열속(heat flux)이 고체 추진제의 표면에 존재하며 이 중의 일부가 고체영역에서 흡수될 때 표면에서의 선형교란을 고려한 ZN(Zeldovich-Novozhilov) 방법을 이용하여 연소불안정 현상을 이론적으로 해석하여 연소불안정 현상을 설명할 수 있는 연소 응답함수를 구하였다. 본 연구에서 얻어진 응답함수를 해석함으로써, Zebrowski등$^{(5)}$ 에 의하여 얻어진 복사열 교란에 대한 응답함수가 과소 평가된 응답특성을 나타내고 있음을 알았다. 또한 응답함수의 고유불안정성을 판별하는 민감계수 r과 k의 영역의 해석으로부터 SOn등$^{(6)}$ 에 의하여 밝혀진 안정 경계선의 안정한 영역보다 본 연구에서 구한 안정 경계영역이 줄어드는 경향을 보여주고 있다. 이것은 (6)에서 과소 평가된 복사열전달의 영향을 수정한 결과 때문이다.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.2
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• pp.52-60
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• 2002

Line heating is a forming process which makes the curved surface with the residual strain created by applying heat source of high temperature to steel plate. in order to control the residual strain, it is necessary to understand not only conductive heat transfer between heat source and steel plate, but also temperature distribution of steel plate. In this paper we attempted to analyze is temperature distribution of steel plate by simplifying a line heating process to collision-effusive flux of high temperature and high velocity, and conductive heat transfer phenomenon. To analyze this, combustion in the torch is simplified to collision effusive phenomenon before analyzing turbulent heat flux. The distribution of temperature field between the torch and steel plate is computed through turbulent heat flux analysis, and the convective heat transfer coefficient between effusive flux and steel plate is calculated using approximate empirical Nusselt formula. The velocity of heat flux into steel plate is computed using the temperature distribution and convective heat transfer coefficient, and temperature field in the steel plate is obtained through conductive heat transfer analysis in which the traction is induced by velocity of heat flux. In this study, Finite Element Method is used to accomplish turbulent heat flux analysis and conductive heat transfer analysis. FEA results are compared with empirical data to verify results.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.59-60
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• 2017

Combustion instability of gas turbine is performed by adopting dynamic mode decomposition (DMD). The unstable frequencies are calculated and compared with FFT results. The damping coefficient derived from the DMD technique and FFT results were compared and analyzed. OH radical is measured by experimental work and fluctuation field is extracted and FTF was calculated at various points with DMD. The gains of FTF are changed depending on the extraction position of the heat release fluctuation field.

• Applied Chemistry for Engineering
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• v.19 no.3
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• pp.338-344
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• 2008

The improvement of energy conservation is mandatory to decrease consumption of fossil fuels and to minimize negative impacts on the environment which originates from large cooling and heating demand. The absorption heat pump technology has a large potential for energy-saving in this respect. Absorption heat pump is a means to upgrade waste heat without the addition of extra thermal energy. The higher performance of absorber is of great importance for absorption heat pump cycle. In this study, in order to improve the performance of absorber, the absorber of tangential feed of a liquid phase with spiral tube has been investigated using methanol-glycerine as a working fluid. The spiral tube and tangential feeding generate the turbulence into the liquid flow while increasing the mass and heat transfer coefficients. The simultaneous heat and mass transfer were found to take place in a liquid turbulent film in the absorber with the spiral tube during the process of gas absorption. By calculating mass and heat transfer coefficients by measurement of the concentration and the temperature of each position in the absorber, the entrance was found to be more effective in enhancing mass and heat transfer.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.12
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• pp.1079-1088
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• 2015

Parallelism and performance enhancement of calculating view factors in KSDS developed by KARI is introduced in this paper. View factor is an essential parameters of radiation thermal analysis for a spacecraft, and the amount of computation of them is not negligible. Especially, independent integration of view factors at each position of the orbit because the relative displace between solar panel and main body of a satellite varies with the position on the orbit. This paper introduces a range of parallelism of computing view factor and their performance, detection of obstructions by spatial search algorithm based on KD-Tree, and the reduction of the calculation of view factors of a satellite with relative motion between solar panel and main body, called updating fractional view factor matrix, for satellite thermal analysis.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.4
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• pp.395-404
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• 2013

In this study, R-410A evaporation heat transfer tests were conducted in flattened tubes made from 5-mm round tubes. The test range covered a saturation temperature of $15^{\circ}C$, heat flux of $5{\sim}15kW/m^2K$, and mass flux of $200-400kg/m^2s$. The results showed that both the condensation heat transfer coefficient and the pressure drop increased as the aspect ratio increased, with a pronounced increase for an aspect ratio of 4. A comparison of the flattened tube data with existing correlations revealed that the heat transfer coefficients were reasonably predicted by the Shah correlation, and the pressure drops were reasonably predicted by the Jung and Radermacher correlation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.12
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• pp.1111-1119
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• 2010

In this study, condensation heat transfer coefficients of R-410A were obtained in flattened tubes made from round tubes with an inner diameter of 5.0 mm. The saturation temperature was $45^{\circ}C$; the heat flux, 10 kW/$m^2K$; the mass flux, 100-400 kg/$m^2s$; and the quality, 0.2-0.8. The results showed that the effect of the aspect ratio on the condensation heat transfer coefficient depended on the flow pattern. For annular flow, the heat transfer coefficient increased as the aspect ratio increased. For stratified flow, however, the reverse was true: the pressure drop increased as the aspect ratio increased. Existing correlations adequately predicted the heat transfer coefficients and pressure drops of the flattened tubes.