• Journal of Advanced Marine Engineering and Technology
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• 제35권2호
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• pp.224-231
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• 2011

핀-휜 구조물이 삽입된 채널은 열전달이 향상되는 것으로 알려져 있다. 복잡한 핀-휜 구조물은 다공성 매체로 모사할 수 있을 만큼 매우 불규칙적인 유동을 보여준다. 본 연구는 수치해석을 통하여 핀-휜 구조물이 삽입된 채널의 열전달과 압력강하의 특성을 분석하였다. 유효유동공간비가 높고 직경이 큰 경우 실험데이터를 잘 예측 하였지만, 유효유동공간비가 낮은 경우 비교적 오차가 큰 편이었다. 유효유동 공간비가 낮을수록 유동교란이 강해져서 열전달이 증가하지만 압력강하도 증가하여 팬의 동력이 증가하기 때문에 최적점을 찾아서 설계하여야 한다. 본 연구에서는 전면유속이 5m/s 일 때, D25 모델에서는 유효유동공간비가 0.5인 지점에서, D05 모델에서는 0.9에서 압력강하가 급격하게 늘어나기 때문에 이보다 더 작은 유효유동공간비에서의 작동은 바람직하지 않다.

• 대한기계학회논문집B
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• 제28권8호
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• pp.961-967
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• 2004

An inclined jet impinging on a pin fin heat sink is proposed and investigated experimentally. To investigate the flow pattern, flow visualization using fluorescence and velocity measurement using particle image velocimetry(PIV) are conducted with water. The jet impinges over a wide span of the heat sink with a large recirculation in the upper free space and occasionally with another smaller one in the upstream corner. Further, thermal experimentation is conducted using air to obtain temperature profiles using a thermocouple rake in the air and using thermal image on the heat sink back plate, with impinging angles of 35, 45 and 55 degrees. The Reynolds number range based on the nozzle slot is varied from 1507 to 6405. The results show that impinging angle of 55 degree shows the largest heat transfer capability. The results of thermal experiment are compared and discussed with those of flow visualization.

• 설비공학논문집
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• 제10권6호
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• pp.743-752
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• 1998

Experiments were performed to characterize single-phase heat transfer behavior of submerged liquid jet with multiple nozzle normally impinging on the smooth and extended surfaces. Arrays of 9 and 36 nozzles were used, with diameters of 0.5 to 2.0mm providing nozzle area ratio (AR) from 0.05 to 0.2. The square pin fin arrays were chosen as extended surfaces and the effects of geometrical parameters such as fin height, the ratio of fin width to channel width on heat transfer enhancement were examined. Single nozzle characteristics were also evaluated for comparison. The results clearly showed that heat transfer enhancement could be realized by using multiple nozzles at the constant volume flow rate. The average Nusselt number of multiple nozzle impingement on the smooth surface was correlated by the following equation : Nu/$Pr\frac{1}{3}=0.94 Re^{0.56}N^{-0.12}AR^{0.50}$The average heat transfer coefficients of multiple nozzle impingement on the extended surfaces decreased with increasing fin height and the ratio of fin width to channel width. The effectiveness of ex-tended surfaces ranged from 1.5 to 3.5 depending on the fin height, the ratio of fin width to channel width of pin fin arrays, nozzle number and nozzle area ratio.

• 설비공학논문집
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• 제15권10호
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• pp.860-869
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• 2003

Design optimization of the heat sink with 7${\times}$7 square pin-fins is performed numerically using the Computational Fluid Dynamics (CFD) and the Computer Aided Optimization (CAO). In the pin-fins heat sink, the optimum design variables for fin height (h), fin width (w), and fan-to-heat sink distance (c) can be achieved when the thermal resistance ($\theta$$_{j}$) at the junction and the overall pressure drop ($\Delta$p) are minimized simultaneously. To complete the optimization, the finite volume method for calculating the objective functions, the BFGS method for solving the unconstrained non-linear optimization problem, and the weighting method for predicting the multi-objective problem are used. The results show that the optimum design variable for the weighting coefficient of 0.5 are as follows: w=4.653 mm, h=59.215 mm, and c=2.667 mm. In this case, the objective functions are predicted as 0.56K/W of thermal resistance and 6.91 Pa of pressure drop. The Pareto optimal solutions are also presented.re also presented.d.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2012년도 제45회 KOSCO SYMPOSIUM 초록집
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• pp.115-118
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• 2012

The configurations of the heat exchanger of the boiler can be determined from the trade-off between the heat transfer area which is related to the capital cost and the pressure drop which is related to operating cost. In this study, 3.5 ton/hr small size marine boiler having concentric annuli tubes is the design boiler. To determine the optimizing point, according to diameter, number, length of tube, heat transfer, pressure drop, operating cost and capital cost have been calculated. Also, when the fin tube is replaced by the bare tube design parameters changed have been calculated.

• 융복합기술연구소 논문집
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• 제7권1호
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• pp.1-6
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• 2017

The Heat exchanger for deep geothermal system is very important to enhance the efficiency of the system. The co-axial heat exchanger is used due to the limitation of digging space. The heat transfer on the external surface of outer pipe should be high to receive a large amount of heat from the ground. However, the inner pipe should be insulated to reduce the heat loss and increase the temperature of discharge water. This study made experiment apparatus to describe the co-axial heat exchanger and measure the heat transfer coefficients on the internal and external surface. And the pin-fin was designed and fixed on the internal surface to increase the efficiency of heat exchanger. Finally, we calculated the temperature of discharge water using the heat transfer circuit of co-axial heat exchanger and heat transfer coefficient which from experimental results. The water temperature was reached the ground temperature at -500 m and following the ground temperature. When the water return to the ground surface, the water temperature was decreased due to heat loss. As the pin-fin case, the heat transfer coefficient on the internal surface was decreased by 30% and it mean that the pin-fin help to insulate the inner pipe. However, the discharge water temperature did not change although pin-fin fixed on the inner pipe.

• 한국유체기계학회 논문집
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• 제13권5호
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• pp.43-53
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• 2010

This study investigates a design optimization of a rotating two-pass rectangular cooling channel with staggered arrays of pin-fins. The radial basis neural network method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer with shear stress transport turbulent model. The ratio of the diameter to height of the pin-fins and the ratio of the streamwise spacing between the pin-fins to height of the pin-fin are selected as design variables. The optimization problem has been defined as a minimization of the objective function, which is defined as a linear combination of heat transfer related term and friction loss related term with a weighting factor. Results are presented for streamlines, velocity vector fields, and contours of Nusselt numbers, friction coefficients, and turbulent kinetic energy. These results show how fluid flow in a two-pass square cooling channel evolves a converted secondary flows due to Coriolis force, staggered arrays of pin-fins, and a $180^{\circ}$ turn region. These results describe how the fluid flow affects surface heat transfer. The Coriolis force induces heat transfer discrepancy between leading and trailing surfaces, having higher Nusselt number on the leading surface in the second pass while having lower Nusselt number on the trailing surface. Dean vortices generated in $180^{\circ}$ turn region augment heat transfer in the turning region and in the upstream region of the second pass. As the result of optimization, in comparison with the reference geometry, thermal performance of the optimum geometry shows the improvement by 30.5%. Through the optimization, the diameter of pin-fin increased by 14.9% and the streamwise distance between pin-fins increased by 32.1%. And, the value of objective function decreased by 18.1%.

• 정보보호학회논문지
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• 제27권4호
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• pp.843-853
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• 2017

"공인인증서 의무 사용" 폐지에 따라 모바일 기반 금융 서비스의 자율성이 높아지면서 다양한 인증 수단이 제공되고 있다. 대표적인 인증 수단으로는 SMS, ARS, PIN, 텍스트 패스워드, 지문 등이 있다. 본 연구에서는 통일된 모바일 환경에서 인증수단의 사용성, 안전성을 분석하였다. 사용성 평가에 있어서 SUS (System Usability Scale), 인터뷰를 통해 평가를 진행하였으며, NIST에서 제시한 전자인증가이드라인을 이용하여 각 인증 수단에 대한 안전성을 평가하였다. 연구 결과 지문 인식 기반 인증 수단이 가장 높은 사용성 등급을 나타내는 Excellent로 평가되었으며, 안전성 분석 결과에서도 지문 인식 기반 인증 수단이 Security Level 4를 획득하여 가장 안전한 인증 수단으로 평가되었다.

• Nuclear Engineering and Technology
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• 제26권2호
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• pp.237-246
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• 1994

KMRR 노심의 열수력 설계 및 안전 해석을 위한 고유량 CHF 상관식을 개발하였다. 상관식 개발에는 fin이 부착된 경우와 부착되지 않은 경우의 가열봉에 대한 단일봉 CHF 실험 자료를 사용하였다. 상관식은 Reynolds 수, 열역학 평형 건도, 액상과 기상의 밀도비 및 등가수력 직경비 등의 무차원 변수로 이루어져 있으며, fin이 있는 경우와 없는 경우의 가열 둘레비를 사용하여 fin의 영향을 고려하였다. 이처럼 단일봉에 대하여 개발된 상관식의 KMRR 핵연료 집합체에 대한 적용 타당성을 보이기 위하여 비가열면 및 축방향 비균일 출력 분포의 영향을 논의하였다. CHF 실험 자료 분석 결과, 상관식 한계 DNBR은 1.44로 결정되었다.

• International Journal of Air-Conditioning and Refrigeration
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• 제13권2호
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• pp.71-82
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• 2005

The shape of $7\times7$ pin-fins heat sink is optimized numerically to obtain the minimum pressure drop and thermal resistance. In this study, the fin height (h), fin width (w), and fan-to-heat sink distance (c) are chosen as the design variables and the pressure drop $({\Delta}P)$ and thermal resistance $(\theta_j)$ are adopted as the objective functions. To obtain the optimum design values, we used the finite volume method for calculating the objective functions, the BFGS method for solving the unconstrained non-linear optimization problem, and the weighting method for predicting the multi-objective problem. The results show that the optimum design variables for the weighting coefficient of 0.5 are as follows: W=4.653 mm, h=59.215mm, and c=2.667mm. The objective functions corresponding to the optimal design are calculated as ${\Delta}P=6.82$ Pa and $(\theta_j)=0.56K/W$. The Pareto solutions are also presented for various weighting coefficients and they will offer very useful data to design the pin-fins heat sink.