• Journal of Magnetics
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• 제12권2호
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• pp.72-76
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• 2007

We investigate the spin transfer torque in metallic multilayer system by employing Keldysh non-equilibrium Green function method. We study the dependences of the spin transfer torque on the detailed energy configuration of ferromagnetic, spacer, and lead layers. With Keldysh non-equilibrium Green function method applied to a single band model, we explore spin transfer torque effect in various layer structures and for various material parameters.

• Journal of Mechanical Science and Technology
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• 제17권4호
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• pp.581-589
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• 2003

Film absorption involves simultaneous heat and mass transfer in the gas-liquid system. While the non-absorbable gas does not participate directly In the absorption process. its pretence does affect the overall heat and mass transfer. An experimental study was performed to investigate the heat and mass transfer characteristics of LiBr-H$_2$O solution flow ing over 6-row horizontal tubes with the water vapor absorption in the pretence of non-absorbable gases. The volumetric concentration of non-absorbable gas, air, was varied from 0.17 to 10.0%. The combined effects of the solution flow rate and its concentration on the heat and mass transfer coefficients were also examined. The presence of 2％ volumetric concentration of air resulted in a 25% reduction in the Nusselt number and 41% reduction in the Sherwood number Optimum film Reynolds number was found to exist at which the heat and mass transfer reach their maximum value independent of air contents. Reduced Nusselt and Sherwood numbers. defined as the ratio of Nusselt and Sherwood numbers at given non-absorbable gas content to that with pure water vapor, were correlated to account for the reduction in the heat and mass transfer due to non-absorbable gases in a falling film absorption process.

• International Journal of Air-Conditioning and Refrigeration
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• 제6권
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• pp.56-66
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• 1998

The absorption process of water vapor in a liquid film is an important process in LiBr-Water absorption system. The composition of the gas phase, in which a non-absorbable gas is combined with the absorbate, influences the transport characteristics. In the present work, the absorption processes of water vapor into aqueous solutions of lithium bromide in the presence of non-absorbable gas are investigated. The continuity, momentum, energy and diffusion equations for the solution film and gas are formulated in integral forms and solved numerically. It is found that the mass transfer resistance in gas phase increases with the concentration of non-absorbable gas. However the primary resistance to mass transfer is in the liquid phase. As the concentration of non-absorbable gas in the absorbate increases, the interfacial temperature and concentration of absorbate in solution decrease, which results in the reduction of absorption rate. The reduction of mass transfer rate is found to be significant for the addition of a small amount of non-absorbable gas to the pure vapor, especially at the outlet of tube where the non-absorbable gas accumulates. At higher non-absorbable gas concentration, the decrease of absorption rate seems to be linear to the concentration of non-absorbable gas.

• 대한기계학회논문집
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• 제19권10호
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• pp.2586-2594
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• 1995

Two phase flow phenomena are observed in many industrial facilities and make much importance of optimum design for nuclear power plant and various heat exchangers. This experimental study has been investigated the classification of the flow pattern, the local void distribution and convective heat transfer in swirl and non-swirl two phase flow under the isothermal and nonisothermal conditions. The convective heat transfer coefficients in the single phase water flow were measured and compared with the calculated results from the Sieder-Tate correlation. These coefficients were used for comparisons with the two-phase heat transfer coefficients in the flow orientations. The experimental results indicate, that the void probe signal and probability density function of void distribution can used into classify the flow patterns, no significant difference in voidage distribution was observed between isothermal and non-isothermal condition in non-swirl flow, the values of two phase heat transfer coefficients increase when superficial air velocities increase, and the enhancement of the values is observed to be most pronounced at the highest superficial water velocity in non-swirl flow. Also two phase heat transfer coefficients in swirl flow are increased when the twist ratios are decreased.

• 기록학연구
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• 제66호
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• pp.69-104
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• 2020

기록관은 처리과에서 생산한 기록물을 영구기록물관리기관으로 이관하기 전까지 관리의 연속성을 보장하는 핵심 기관이며, 기록물의 이관은 매년 이루어지는 기록관의 주요 업무이다. 2008년 업무관리시스템 도입으로 기록물의 전자적 생산·관리체계가 구축되었고, 비전자기록물은 업무관리시스템에 등록하여 전자적으로 관리하게 되었다. 이 연구는 함양교육지원청 기록관의 2017~2019년 비전자기록물 이관업무 프로세스와 이관목록 분석을 통해 비전자기록물의 전자적 관리실태를 파악하고 이관업무 개선방안을 제시하였다.

• 대한기계학회논문집B
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• 제22권4호
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• pp.489-498
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• 1998

Among the heat/mass exchange units composing an absorption system, the absorber, where the refrigerant vapor is absorbed into the liquid solution is the one least understood. In the present study, the effects of non-absorbable gas on the absorption process of aqueous lithium bromide solution falling film inside a vertical tube were experimentally investigated. In the range of film Reynolds number of 30 ~ 195, heat and mass transfer characteristics were investigated as a function of non-absorbable gas volumetric concentration, 0.2 ~ 20%. An increase of non-absorbable gas volumetric concentration degraded the mass transfer rate dramatically in the absorption process. The reduction of mass transfer rate was significant for the addition of small amount of non-absorbable gas to the pure vapor. At film Reynolds number of 130, an increase of non-absorbable gas concentration from 0.2 to 6.0% resulted in the decrease of mass transfer rate by 36% and 20% of non-absorbable gas by 59%. However the decrease of film Nusselt number with the increase of volumetric concentration of non absorbable gas was relatively smaller than the decrease of Sherwood number. Critical film Reynolds number was identified to exist for the maximum heat and mass transfer regardless of the volumetric concentration of non-absorbable gases.

• 설비공학논문집
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• 제24권7호
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• pp.553-559
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• 2012

A plate-fin heat exchanger is a type of heat exchanger widely used in air conditioners, and tubes and fins are tightly assembled by the mechanical expansion process of tubes. The tube expansion process deforms the grooves inside the tube, and the groove shapes also affect the adhesion between tubes and fins. In this study, the adhesion and heat transfer performance affected by the tube expansion of the non-uniform groove shape tube with different heights are investigated by both analysis and experiments. From the analysis method, it was shown that the contact pressure of non-uniform groove tube is higher than that of the uniform groove tube, and the most appropriate high groove number of the non-uniform groove tube is designed for the maximum contact pressure. From the experimental results, the decreasing rate of the condensation heat transfer coefficient is smaller in the non-uniform groove tube with different heights, compared to the conventional uniform groove tube. Also, the air-side heat transfer coefficient of the non-uniform groove tube with different heights is higher than that of the uniform groove tubes.

• 대한기계학회논문집B
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• 제22권4호
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• pp.499-509
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• 1998

In the absorption process of water vapor in a liquid film, the composition of the gas phase, in which a non-absorbable gas is combined with the absorbate influences the transport characteristics remarkably. In the present study, the absorption processes of water vapor into aqueous solution of lithium bromide in the presence of non-absorbable gases were investigated analytically. The continuity, momentum, energy and diffusion equations for the solution film and gas phase were formulated in integral forms and solved numerically. It was found that the mass transfer resistance in gas phase increased with the concentration of non-absorbable gas. However the primary resistance to mass transfer was in the liquid phase. As the concentration of non-absorbable gas in the absorbate increased, the liquid-vapor interfacial temperature and concentration of absorbate in solution decreased, which resulted in the reduction of absorption rate. The reduction of mass transfer rate was found to be significant for the addition of a small amount of non-absorbable gas to the pure vapor, especially at the outlet of an absorber where non-absorbable gases accumulated. At higher non-absorbable gas concentration, the decrease of absorption flux was almost linear to the volumetric concentration of non-absorbable gas.

• 디지털융복합연구
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• 제12권12호
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• pp.449-456
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• 2014

본 연구에서는 관할구역 인구분포와 대비하여 출동건수를 파악하였으며, 출동하여 실제 병원으로 이송한 비율을 파악함으로서, 실제 인구현황과 출동건수와 병원 이송환자의 비율 관계를 분석하였다. 본 연구를 위해, 우리는 2010년 1월부터 2012년 12월까지 3년 동안 대상 지역인 D광역시 소재 5개 소방서별 출동건수를 파악하였으며, 출동현황을 병원 이송과 미 이송으로 데이터를 분석했다. J 소방서에서 출동건수가 가장 높게 나타났으며, 병원 이송건수와 미 이송 건수에서도 가장 높게 나타나는 경향을 볼 수 있었다. 반대로, B 소방서에서 가장 낮게 나타났다. 관할구역 인구수에서는 S소방서 관할구역 인구수가 가장 많았으며, D소방서 관할구역 인구수가 가장 적게 나타났다. 결론적으로 총 출동건수에 의해 병원 이송 건수와 병원 미 이송건수가 유의하게 증감하는 것을 확인하였으며, 인구수에 의한 상관관계는 없는 것으로 나타났다.

• 대한기계학회논문집
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• 제19권7호
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• pp.1770-1779
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• 1995

A combined convective heat transfer study for non-Newtonian fluids was experimentally performed in uniformly heated horizontal tubes with laminar flow in the thermal entry region. Velocity profiles were fully developed at the entrance of the heated sections in the tubes. Aqueous solutions of sodium carboxymethylcellulose(CMC ) were used; their behavior showed a reasonably good fit into the power-law model, .tau.=K.gamma.$^{n}$ . The test sections were made of copper with inside diameters of 3.23 cm and 5.042 cm and lengths of approximately 300 cm. Most experimental runs displayed noticeable secondary flows caused by buoyancy ; when present, secondary flows caused significant increase in the rate of heat transfer over the purely forced-convection case. A correlation, which relates the rate of heat transfer for flows with temperature-dependent properties, free convection effects, and non-newtonian effects, was suggested.