• 설비공학논문집
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• 제15권6호
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• pp.510-517
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• 2003

An experimental study on the pressure drop during flow boiling for pure refrigerants R134a and Rl23, and their mixture was carried out in a uniformly heated horizontal tube. Tests were run at a pressure of 0.6 MPa and in the ranges of heat flux 5~50 kW/m$^2$, vapor quality 0~100 percent and mass velocity of 150~600 kg/m$^2$s. Generally, the two-phase frictional multiplier is used to predict the frictional pressure drop during the two-phase flow boiling. The obtained results have been compared to the existing various correlations for the two-phase multiplier. Also, the frictional pressure drop was compared to a few available correlations; The Lockhart-Martinelli correlation considerally overpredicted the frictional pressure drop data for mixture as well as pure components in the entire mass velocity ranges employed in the present study, while the Chisholm correlation underpredicted the present data. The Friedel correlation was found to satisfactorily correlate the frictional pressure drop data except for a low quality region.

• 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.

• 수산경영론집
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• 제43권3호
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• pp.31-41
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• 2012

This paper was conducted to study the economic valuation for Nursery-Phase production of the tidal flat oyster in Korea. Benefit-cost(B/C) model used to indicate the effects of economic valuation. Using discounting rates(i.e., 4.5%, 6.5% and 8.5%), the model compared revenues and costs that occur at different times from 2012 to 2018. This study also estimated various submodels, which are Benefit Cost Ratio(B/C ratio), Net Present Value(NPV), Internal Ration of Return(IRR), to compare profit of Nursery-Phase production styles and analyzed returns to evaluate the scenarios. Sensitivity analysis were conducted for various scenarios. The results suggest as follows. First, the oyster spat to the shell height of 3~5cm was more profit than the shell height of 1~3cm. Second, all of sensitivity analysis with submodels were economic valuation such that B/C ratio > 1, NPV > 0 and IRR > discounting rate. Third, the payback period was about 3years after installed Nursery-Phase production system.

• 한국전산유체공학회지
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• 제14권4호
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• pp.13-22
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• 2009

A two-phase (gas and liquid) flow analysis solver, named CUPID, has been developed for a realistic simulation of transient two-phase flows in light water nuclear reactor components. In the CUPID solver, a two-fluid three-field model is adopted and the governing equations are solved on unstructured grids for flow analyses in complicated geometries. For the numerical solution scheme, the semi-implicit method of the RELAP5 code, which has been proved to be very stable and accurate for most practical applications of nuclear thermal hydraulics, was used with some modifications for an application to unstructured non-staggered grids. This paper is concerned with the effects of interpolation schemes on the simulation of two-phase flows. In order to stabilize a numerical solution and assure a high numerical accuracy, the second-order upwind scheme is implemented into the CUPID code in the present paper. Some numerical tests have been performed with the implemented scheme and the comparison results between the second-order and first-order upwind schemes are introduced in the present paper. The comparison results among the two interpolation schemes and either the exact solutions or the mesh convergence studies showed the reduced numerical diffusion with the second-order scheme.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 C
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• pp.1426-1427
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• 2006

Chalcogenide based phase-change memory has a high capability and potential for the next generation nonvolatile memory device. Fast writing speed, low writing voltage, high sensing margin, low power consume and long cycle of read/write repeatability are also good advantages of nonvolatile phase-change memory. We have been investigated the new material for the phase-change memory. Its composition is consists of chalcogenide $Ge_{1}Se_{1}Te_2$ material. We made this new material to solve problems of conventional phase-change memory which has disadvantage of high power consume and high writing voltage. In the present work, we are manufactured $Ge_{1}Se_{1}Te_{2}/Ge_{2}Sb_{2}Te_{5}/Ge_{1}Se_{1}Te_{2}$ and $Ge_{2}Sb_{2}Te_{5}/Ge_{1}Se_{1}Te_{2}/Ge_{2}Sb_{2}Te_{5}$ sandwich triple layer structure devices are manufactured to investigate its electrical properties. Through the present work, we are willing to ensure a potential of substitutional method to overcome a crystallization problem on PRAM device.

• 전기학회논문지
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• 제66권3호
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• pp.587-592
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• 2017

In the three-phase four-wire low-voltage power distribution equipment, single-phase and three-phase load have been used mainly mixed. Also linear and nonlinear loads have been used together in the same conditions. In a three-phase four-wire distribution line, the current distribution of three-phase linear load is almost constant in each phase during driving or stopping, but the single-phase load is different from each other for each phase in accordance with the operation and stop. So that the voltage unbalance is caused by the current difference of each phase. In the three-phase four-wire distribution system, non-linear load is used with linear load. The presence of single-phase nonlinear loads can produce an increase in harmonic currents in three-phase and neutral line. It can also cause voltage unbalance. In the present study, we analyzed for the voltage unbalance fluctuations by the operation pattern of the single and three-phase linear and non-linear load in three-phase four-wire low voltage distribution system.

• 한국전산유체공학회지
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• 제6권4호
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• pp.8-14
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• 2001

The phenomena of two-phase suspension flows appear widely in nature and industrial processes. Hence, it is of great importance to understand the mechanism of the gas-solid two-phase flows. In the present study, the numerical simulation has been approached by utilizing the Eulerian-Lagrangian methodology for describing the characteristics of the fluid and particulate phases in a vertical pipe and a 90°square-sectioned bend. The continuous phase(gas phase) is described by the Eulerian formulation and a κ-ε turbulence model is employed to find mean and turbulent properties of the gas phase. The particle properties(velocity and trajectory) are then described by a Lagrangian approach and computed using the mean velocity and turbulent fluctuating velocity of the gas phase. The predictions are compared with measurements by laser-Doppler velocimeter for the validation. As a result, the calculated results show good agreements.

• 열처리공학회지
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• 제21권1호
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• pp.26-32
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• 2008

Effects of annealing treatment on microstructure and mechanical property of co-sputtered TiNi thin films were studied. As-deposited films showed amorphous state. However, above annealing temperature of $500^{\circ}C$ martensite phase (B19'), precipitate phase ($Ti_2Ni$) and a small amount of parent phase ($B_2$) were present, and phase transformation behaviors were three multi-step phase transformations $B19^{\prime}{\rightarrow}B_2$ and $B_2{\rightarrow}R-phase$ and $R-phase{\rightarrow}B19^{\prime}$. Increase of martensite transformation temperature, increase of microhardness and Young's modulus of TiNi films annealed above $500^{\circ}C$ were discussed in terms of precipitate phase.

• International Journal of Precision Engineering and Manufacturing
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• 제2권4호
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• pp.81-88
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• 2001

We present a new digital phase measuring method for heterodyne optical interferometry, which providers high measuring speed up to 6 m/s with a fine displacement resolution of 0.1 nanometer. The key idea is combining two distinctive digital phase measuring techniques with mutually complementary characteristics to earth other one is counting the Doppler shift frequency counting with 20 MHz beat frequency for high-velocity measurement and the other is the synchronous phase demodulation with 2.0 kHz beat frequency for extremely fine displacement resolution. The two techniques are operated in switching mode in accordance wish the object speed in a synchronized way. Experimental results prove that the proposed dual mode phase measuring scheme is realized with a set of relatively simple electronic circuits of beat frequency shifting, heterodyne phase detection. and low-pass filtering.

• 한국통신학회논문지
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• 제31권3C
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• pp.237-244
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• 2006

본 논문에서는 2차원 결합 가우시안 Q-함수(Two-dimensional joint Gaussian Q-function)를 이용하여 AWGN(Additive White Gaussian Noise) 환경에서 M-PSK(M-ary Phase Shift Keying) 신호의 I/Q 위상 불균형(Phase unbalance) 존재 시 수치 적분이 필요 없는 정확하고 일반화된 closed-form 형태의 비트 오류율(Bit Error Rate) 표현을 유도한다. 새롭게 유도된 표현은 평균 BER 뿐만 아니라 k-번째 비트의 BER에 대하여도 일반화된 식으로 되어 있어 다양한 환경으로의 적용이 용이하여 M-PSK를 적용하는 많은 디지털 통신 시스템에서 복조 시 발생할 수 있는 I/Q 위상 불균형에 의한 시스템 성능 변화에 대하여 정확한 이론적 성능 기준을 제공할 것으로 기대된다.