• Korean Chemical Engineering Research
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• 제45권1호
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• pp.17-24
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• 2007

본 연구의 목적은 제지공정에서 건조 실린더의 모델을 규명하고 입력변수들에 대한 공정의 응답 특성을 분석하는 것이다. 모델의 규명은 실제 공장의 운전 데이터에 근거하였는데 건조공정에서는 실린더로 공급되는 수증기의 압력이 주요 변수가 된다. 수증기 응축액으로부터 캔버스로의 열전달 계수는 실린더 및 웹과 펄프의 열 전도도와 운전 데이터에 근거하는 실험식으로 나타낼 수 있음이 밝혀졌다. 실린더 모델은 측정되는 수분함량과 웹 온도를 이용하여 검증하였으며 건조 공정의 안정성은 실린더 모델로부터 얻은 전달함수로부터 확인하였다.

• 한국연소학회지
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• 제16권2호
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• pp.1-8
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• 2011

As one of the main technologies for carbon capture and storage in power generation, oxy-coal combustion is being developed for field demonstration in Korea. This study presents the results of numerical simulation for combustion in a single-wall-fired 100 $MW_e$-scale boiler proposed for the initial design of the demonstration plant. Using a commercial CFD code, the detailed combustion, flow and heat transfer characteristics were assessed both for air-mode and oxy-mode combustion. The results show that stable combustion can be achieved in the dual mode operation with the current boiler configuration. However, the differences in the flow pattern and heat transfer between the two combustion modes need to be considered in the design and operation which is mainly due to the larger density and specific heat of $CO_2$ compared to $N_2$. Further development of the boiler design is required using improved numerical modeling for radiative heat transfer and combustion.

• 설비공학논문집
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• 제18권5호
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• pp.384-392
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• 2006

Reported are the heat transfer characteristics of a two-phase loop thermosyphon (TLT) with nanofluids consisted of nano-size silver particles and distilled water as the working fluid. The nanofluids used in the present study are dispersed solutions with various amount of silver nanoparticle in distilled water. It is seen from the present study that the heat transfer performance of the test TLT with nanofluids increased as much as about 2 times higher than that of a TLT with pure water as the working fluid based on same heat flux. The study also showed that there was no deterioration of the TLT performance with time, up to a period of 8 days of continuous operation which implies that there was no coagulation of nanoparticles within the working nanofluid during the operation of the test TLT.

• Journal of Power Electronics
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• 제19권3호
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• pp.655-664
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• 2019

In order to analyze the nonlinear phenomena of the bifurcation and chaos caused by the switching of nonlinear switching devices in inductively coupled power transfer (ICPT) systems, a Jacobian matrix model, based on discrete mapping numerical modeling, is established to judge the system stability of the periodic closed orbit and to study the nonlinear behavior of Hopf bifurcation in a system under full resonance. The general flow of the parameter design, based on the stability principle for ICPT systems, is proposed to avoid the chaos and bifurcation phenomena caused by unreasonable parameter selection. Firstly, based on the state equation of SS-type compensation, a three-dimensional bifurcation diagram with the coupling coefficient as the bifurcation parameter is established with a numerical simulation to observe the nonlinear phenomena in the system. Then Filippov's method based on a Jacobian matrix model is adopted to deduce the boundary of stable operation and to judge the type of the bifurcation in the system. Then the general flow of the parameter design based on the stability principle for ICPT systems is proposed through the above analysis to realize stable operation under the conditions of weak coupling. Finally, an experimental platform is built to confirm the correctness of the numerical simulation and modeling.

• Nuclear Engineering and Technology
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• 제56권2호
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• pp.762-769
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• 2024

The TMSR-SF0 simulator is an integral effect thermal-hydraulic experimental system for the development of thorium molten salt reactor (TMSR) program in China. The simulator has two heat transport loops with liquid FLiNaK. In literature, the 95% level confidence uncertainties of the thermophysical properties of FLiNaK are recommended, and the uncertainties of density, heat capacity, thermal conductivity and viscosity are ±2%, ±10, ±10% and ±10% respectively. In order to investigate the effects of thermophysical properties uncertainties on the molten salt heat transport system, the uncertainty and sensitivity analysis of the heat transfer characteristics of the simulator system are carried out on a RELAP5 model. The uncertainties of thermophysical properties are incorporated in simulation model and the Monte Carlo sampling method is used to propagate the input uncertainties through the model. The simulation results indicate that the uncertainty propagated to core outlet temperature is about ±10 ℃ with a confidence level of 95% in a steady-state operation condition. The result should be noted in the design, operation and code validation of molten salt reactor. In addition, more experimental data is necessary for quantifying the uncertainty of thermophysical properties of molten salts.

• 방송공학회논문지
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• 제27권1호
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• pp.104-123
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• 2022

신경망 기반 스타일 전이 기법은 영상의 고차원적 구조적 특징을 반영하여 높은 품질의 스타일 전이 결과를 제공함으로써 최근 크게 주목받고 있다. 본 논문은 이러한 신경망 기반 스타일 전이의 GPU 메모리 제한에 따른 해상도 한계에 대한 문제를 다룬다. 신경망 출력이 가진 제한적 수용장 특징을 바탕으로, 부분 영상 기반의 스타일 전이 손실함수 경사도 연산이 전체 영상을 대상으로 구한 경사도 연산과 동일한 결과를 생성할 수 있을 것으로 기대할 수 있다. 이러한 아이디어를 기반으로, 본 논문에서는, 스타일 전이 손실함수의 각 구성 요소에 대한 경사도 연산 구조를 분석하고, 이를 통해 부분 영상의 생성 및 패딩에 대한 필요조건을 구하고, 전체 영상의 신경망 출력에 좌우되는 경사도 연산 요구 데이터를 확인하여 구조화함으로써 재귀적 초고해상도 스타일 전이 알고리즘을 개발하였다. 제안된 기법은, 사용하는 GPU 메모리가 처리할 수 있는 크기로 초고해상도 입력을 분할하여 스타일 전이를 수행함으로써, GPU 메모리 한계에 따른 해상도 제한을 받지 않으며, 초고해상도 스타일 전이에서만 감상할 수 있는 독특한 세부 영역의 전이 스타일 특징을 제공할 수 있다.

• Journal of Mechanical Science and Technology
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• 제17권11호
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• pp.1739-1745
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• 2003

The boiling heat transfer characteristics of two-phase closed thermosyphons with internal grooves are studied experimentally and a simple mathematical model is developed to predict the performance of such thermosyphons. The study focuses on the boiling heat transfer characteristics of a two-phase closed thermosyphons with copper tubes having 50, 60, 70, 80, 90 internal grooves. A two-phase closed thermosyphon with plain copper tube having the same inner and outer diameter as those of grooved tube is also tested for comparison. Methanol is used as working fluid. The effects of the number of grooves, the operating temperature, the heat flux are investigated experimentally. From these experimental results, a simple mathematical model is developed. In the present model, boiling of liquid pool in the evaporator is considered for the heat transfer mechanism of the thermosyphon. And also the effects of the number of grooves, the operating temperature, the heat flux are brought into consideration. A good agreement between the boiling heat transfer coefficient of the thermosyphon estimated from experimental results and the predictions from the present mathematical model is obtained. The experimental results show that the number of grooves and the amount of the working fluid are very important factors for the operation of thermosyphons. The two-phase closed thermosyphon with copper tubes having 60 internal grooves shows the best boiling heat transfer performance.

• 대한교통학회지
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• 제32권3호
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• pp.179-186
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• 2014

본 연구에서는 대구시의 지하철과 버스간의 환승통행을 대상으로 환승통행특성을 분석하고 또한 다중회귀분석을 통해 버스와 지하철간의 환승통행량에 영향을 미치는 요인을 분석하여 이를 통한 대중교통환승센터에서 보다 많은 환승통행량이 처리될 수 있는 방안에 대해 모색하였다. 그 결과 환승시간은 환승통행량과 반비례하는 반면, 연계버스 노선수, 지하철역의 공간적 위치, 버스노선의 연계지수는 비례관계가 있는 것으로 나타났다. 또한 표준화계수로부터 지하철역과 연계되는 버스노선의 특성을 반영한 버스노선의 연계지수가 가장 많은 영향을 미친다는 것을 알 수 있었다.

• Journal of Mechanical Science and Technology
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• 제16권9호
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• pp.1102-1111
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• 2002

The study focuses on the heat transfer performance of two-phase closed thermosyphons with plain copper tube and tubes having 50, 60, 70, 80, 90 internal grooves. Three different working fluids(distilled water, methanol, ethanol) are used with various volumetric liquid fill charge ratio from 10 to 40%. Additional experimental parameters such as operating temperature and inclination angle of zero to 90 degrees are used for the comparison of heat transfer performance of the thermosyphon. Condensation and boiling heat transfer coefficients, heat flux are obtained using experimental data for each case of specific parameter. The experimental results are assessed and compared with existing correlations. The results show that working fluids, liquid fill charge ratio, number of grooves and inclination angle are very important factors for the operation of thermosyphons. The relatively high rate of heat transfer is achieved when the thermosyphon with internal grooves is used compared to that with plain tube. The optimum liquid fill charge ratio for the best heat transfer performance lies between 25% and 30%. The range of the optimum inclination angle for this study is 20$^{\circ}$～30$^{\circ}$ from the horizontal position.

• 전력전자학회논문지
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• 제24권4호
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• pp.279-285
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• 2019

This study proposes an enhanced switching pattern that can improve energy transfer efficiency in an active cell-balancing circuit using a multiwinding transformer. This balancing circuit performs cell balancing by transferring energy stored in a specific cell with high energy to another cell containing low energy through a multiwinding transformer. The circuit operates in flyback and buck-boost modes in accordance with the energy transfer path. In the conventional flyback mode, the leakage inductance of the transformer and the stray inductance component of winding can transfer energy to an undesired path during the balancing operation. This case results in cell imbalance during the cell-balancing process, which reduces the energy transfer efficiency. An enhanced switching pattern that can effectively perform cell balancing by minimizing the amount of energy transferred to the nontarget cells due to the leakage inductance components in the flyback mode is proposed. Energy transfer efficiency and balancing speed can be significantly improved using the proposed switching pattern compared with that using the conventional switching pattern. The performance improvements are verified by experiments using a 1 W prototype cell-balancing circuit.