• 태양에너지
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• 제18권3호
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• pp.205-215
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• 1998

Entrainment in thermosyphons and heat pipes was characterized in view of the interfacial stability associated with the critical Weber number and the entrainment limit at the onset of liquid entrainment from the liquid or wicked interface. Both literature review and theoretical analysis on the entrainment models were peformed in order to evaluate accuracy of the predicted value. For this purpose, the models were categorized in two groups according to their entrainment mechanism and interfacial configurations, i.e., the wave-induced entrainment and the shear-induced entrainment, respectively. Thus, the twelve models(five models for the wave-induced entrainment and seven for the shear induced entrainment) were examined to obtain individual trends and their discrepancies from the general tendency of the overall models. As a result, the critical Weber numbers and entrainment limits were calculated and represented as a function of vapor temperature for the chosen characteristic dimensions of the interface.

• 대한기계학회논문집
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• 제12권3호
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• pp.599-606
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• 1988

본 연구에서는 공기와 물을 사용한 근사수평 반류성층유동에서의 계면파 구조 를 측정하였다. 3차원파 영역내의 유동조건하에서 탐침접촉법을 이용하여 계면파의 액막분포도를 구하였으며 Gauss 모델과 비교분석하였다. 또 이 분포도에서 파의 구 조와 관련된 통계치, 즉 평균액막두께, 파진폭, 파고 교란강도등을 계산하여 유동조건 에 따른 경향을 분석하였다. 본 연구와 병행하여 계면전단응력과 계면마찰계수에 관 한 실험을 수행하였는데 이 결과와 계면파 구조와의 상호연관성도 고찰하였다.

• 대한기계학회논문집A
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• 제25권7호
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• pp.1055-1063
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• 2001

When the interfacial crack of isotropic/orthotropic bi-materials is propagated with constant velocity along the interface, stress and displacement components are derived in this research. The dynamic photoelastic experimental hybrid method for the bimaterial is introduced. It is assured that stress components and dynamic photoelastic hybrid developed in this research are valid. Separating method of stress components is introduced from only dynamic photoelastic fringe patterns. Crack propagating velocity of interfacial crack is 69∼71% of Rayleigh wave velocity of epoxy resin. The near-field stress components of bonded interface of bimaterial are similar with those of pure isotopic material and two dissimilar isotropic bimaterials under static or dynamic loading, but very near-field stress components of bonded interface of bimaterial are different from those.

• 설비공학논문집
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• 제10권4호
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• pp.431-439
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• 1998

Falling film absorption process is an important problem in application such as absorption chillers. The presence of waves on the film affects the absorption process significantly. In the present study the characteristics of heat and mass transfer in laminar-wavy falling film were studied numerically. The wavy flow behavior was incorporated in the energy and diffusion equation. The numerical solution indicated that the interfacial wave increased the transfer rates remarkably. Interfacial shear stress and wave frequency seemed to be the dominant factors on the film Nusselt number and Sherwood number in the wavy film. A comparison of the transfer rates of the wavy film to that of the smooth film showed that the mass transfer rate could be increased by more than 50%.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1286-1291
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• 2004

In order for studying pressure-coupled dynamic responses of droplet vaporization, open-loop experiment of an isolated droplet vaporization exposed to pressure perturbations in stagnant gaseous environment is numerically conducted. Governing equations are solved for flow parameters at gas and liquid phases separately and thermodynamic parameters at the interfacial boundary are matched for problem closure. For high-pressure effects, vapor-liquid interfacial thermodynamics is rigorously treated. A series of parametric calculations in terms of mean pressure level and wave frequencies are carried out employing a n-pentane droplet in stagnant gaseous nitrogen. Results show that wave instability in view of pressure-coupled vaporization response seems more susceptible at higher pressures and higher wave frequencies. Mass evaporation rate responding to pressure waves is amplified with increase in pressure due to substantial reduction in latent heat of vaporization. Augmentation of perturbation frequency also enhances amplification due to the reduction of phase differences between pressure perturbation and surface temperature fluctuation.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.155-164
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• 2004

In order for studying pressure-coupled dynamic responses of droplet vaporization, open-loop experiment of an isolated droplet vaporization exposed to pressure perturbations in stagnant gaseous environment is numerically conducted, Governing equations are solved for flow parameters at gas and liquid phases separately and thermodynamic parameters at the interfacial boundary are matched for problem closure. For high-pressure effects, vapor-liquid interfacial thermodynamics is rigorously treated. A series of parametric calculations in terms of mean pressure level and wave frequencies are carried out employing a n-pentane droplet in stagnant gaseous nitrogen. Results show that wave instability in view of pressure-coupled vaporization response seems more susceptible at higher pressures and higher wave frequencies. Mass evaporation rate responding to pressure waves is amplified with increase in pressure due to substantial reduction in latent heat of vaporization. Augmentation of perturbation frequency also enhances amplification due to the reduction of phase differences between pressure perturbation and surface temperature fluctuation.

• 비파괴검사학회지
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• 제28권6호
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• pp.504-511
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• 2008

This paper proposes an ultrasonic measurement method for measurement of linear interfacial stiffness of contacting surface between two steel plates subjected to nominal compression pressures. Interfacial stiffness was evaluated by using shear waves reflected at contact interface of two identical solid plates. Three consecutive reflection waves from solid-solid surface are captured by pulse-echo method to evaluate the state of contact interface. A non-dimensional parameter defined as the ratio of their peak-to-peak amplitudes are formulated and used to calculate the quantitative stiffness of interface. Mathematical model for 1-D wave propagation across interfaces is developed to formulate the reflection and transmission waves across the interface and to determine the interfacial stiffness. Two identical plates are fabricated and assembled to form contacting surface and to measure interfacial stiffness at different states of contact pressure by means of bolt fastening. It is found from experiment that the amplitude of interfacial stiffness is dependent on the pressure and successfully determined by employing pulse-echo ultrasonic method without measuring through-transmission waves.

• Journal of Advanced Marine Engineering and Technology
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• 제38권8호
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• pp.981-994
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• 2014

Density currents formed by buoyancy discharges from rivers are numerically studied using non-dimensional two layer model including Coriolis acceleration, bottom stress, interfacial friction. Some typical numbers such as Froude number, densimetric Froude number and Kelvin number are obtained and some characteristic scales are defined as a result of non-dimensionalization of the governing equations. Besides the Coriolis effect, the configurations of bottom topography, bottom friction coefficient and interfacial friction are found to significantly affect the propagation of the warm water plume. Frontal position can fastly propagate in the case of large density difference between the two layers and small interfacial friction. Left side boundary current is easily formed under the small interfacial friction. With large Kelvin number, both right and left side boundary currents are formed. Wave-like disturbances and eddies are easily formed under the high Froude number.

• 대한기계학회논문집A
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• 제25권3호
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• pp.434-442
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• 2001

When the interfacial crack of two dissimilar isotropic bi-materials is propagated with constant velocity along the interface, stress and displacement components are derived in this research. The dynamic photoelastic experimental hybrid method for bimaterial is introduced. It is assured that stress components and dynamic photoelastic hybrid method developed in this research are valid. Separating method of stress component is introduced from only dynamic photoelastic fringe patterns. Crack propagating velocity of interfacial crack is 80∼85% (in case of aluminum, 24.3∼25.9%) of Rayleigh wave velocity of epoxy resin. The near-field stress components of crack-tip are similar with those of pure isotropic material under static or dynamic loading, but very near-field stress components of crack-tip are different from those.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2007년도 The 1st International Symposium on Advanced Magnetic Materials
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• pp.160.2-160.2
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• 2007