• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.4
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• pp.920-926
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• 1990

본 연구에서는 Fig.1과 같은 2상 자연순환 회로의 1차원 해석을 수행하고, 액 상의 과냉정도와 각 상 영역에서의 밸브 마찰저항이 순환유속에 미치는 영향을 살펴보 므로써 정적 불안정의 조건을 알아보는데 있다. 본 모델에서는 유한 길이를 갖는 증 발기와 응축기를 고려하였으며, 정적 불안정의 가능성을 해석적으로 보여주기 위해 간 단한 모델(point-heat-source/sink)도 함께 다루었다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.6
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• pp.465-474
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• 2014

To validate the accuracy of the boiling heat flux partitioning model, an experiment was performed to investigate how the wall heat flux is divided into the three heat transfer modes of evaporation, quenching, and single-phase convection during subcooled nucleate boiling on a vertical wall. For the experimental partitioning of the wall heat flux, the wall heat flux and liquid-vapor distributions were simultaneously obtained using synchronized infrared thermometry and the total reflection technique. Boiling experiments of water with subcooling of $10^{\circ}C$ were conducted under atmospheric pressure, and the results obtained at the wall superheat of $12^{\circ}C$ and average heat flux of $283kW/m^2$were analyzed. There was a large difference in the heat flux partitioning results between the experiment and correlation, and the bubble departure diameter and bubble influence factor, which account for a portion of the surrounding superheated liquid layer detached by the departure of a bubble, were found to be important fundamental boiling parameters.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.132-137
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• 2006

Supercooled type ice slurry system is hard to keep a proper supercooling degree when solution becomes supercooling state. This is the reason of the ice blockage in pipe or cooling part due to an unstable cooling state. In this study, a cooling experiment was performed to pressurized solution in a stationary state. The behaviors during the supercooled aqueous solution were investigated at fixed flow rate of brine and aqueous solution of ethylene glycol 7 mass%. Also the effect to the freezing point of supercooled aqueous solution was investigated to the different pressure 101, 202, 303, and 404 kPa. At results, the pressure of the aqueous solution in the cylinder increased the supercooling degree increased and dissolution of supercooled point decreased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.1
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• pp.81-88
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• 2014

An experimental study is performed to obtain an average heat transfer coefficient around the perimeter of a near horizontal tube. For the test a stainless steel tube of 50.8 mm diameter submerged in water at atmospheric pressure is used. Both subcooled and saturated pool boiling conditions are considered and the inclination angle of the tube is changed from the horizontal position to $9^{\circ}$ in steps of $3^{\circ}$. In saturated water, the local boiling heat transfer coefficient at the azimuthal angle of $90^{\circ}$ from the tube bottom can be regarded as the average of the coefficients regardless of the tube inclination angles. However, when the water is subcooled the location for the average heat transfer coefficient depends on the inclination angle and the heat flux. It is explained that the major mechanisms changing the heat transfer are closely related with the intensity of the liquid agitation and the generation of big size bubbles through bubble coalescence.

• Journal of the Korean Ceramic Society
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• v.39 no.5
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• pp.498-502
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• 2002

Pure-yttrium iron garnet($Y_3Fe_5O_{12}$2, YIG) thick films were grown from a $PbO/B_2O_3$ flux onto (111) SGGG substrate using liquid phase epitaxy. The effect of substrate rotation speed and supercooling on crystallinity, chemical composition and growth rate of the thick films was investigated. The FWHM of films decreased with increasing of growth temperature from 860 to 910${\circ}C$. A substrate rotation speed of 120 rpm at 910${\circ}C$ lead to growth rates up to $60{\mu}m/h$.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.9
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• pp.1021-1026
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• 2014

In this paper, among various systems applying hot-gas bypass control, outdoor temperature, outlet temperature of water cooler, superheating and subcooling degree, which are the factors affecting the performance of the system bypassing hot-gas to evaporator inlet were analyzed. The main results were summarized as following. Frist of all, performance of refrigeration system bypassing hot-gas to evaporator inlet was affected by outdoor temperature, outlet temperature of water cooler, superheating and sub cooling degree. Thus, providing basic planning date of refrigeration system obtained through optimization of variables is expectable. Thus, providing the basic design data of refrigeration system can be offered by performing the optimization of these variables. Also, the feasibility of this refrigeration system proposed in this paper was obtained by analyzing operating characteristics of the system bypassing hot-gas to evaporator inlet.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.13 no.3
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• pp.141-147
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• 1984

2차원 채널 입구에서의 꿰떼 난류 유동하는 찬 물 위를, 같은 방향으로 빠르게 난류 유동하는 수증기의 응축은 액체필름 초기상태의 과냉 정도에 의하여서 응축능력이 정하여진다. 수증기와 액체의 채널 입구에서의 균일한 속도 및 온도, 그리고 채널 입구에서 액체와 증기가 차지하는 체적비, 즉 액체필름과 채널 높이를 알고 있을 때, 하류로 유동하면서 응축이 일어나는 현상을 예측하는 모델을 제안하고, 실험치와 비교한 것이다. 채널 입구에서 윗쪽으로는 더운 기체, 아래쪽으로는 찬 액체가 평행한 방향으로 유동하면서 접촉하고 평균적인 액체필름의 두께와 단열된 채널 벽체를 가정하여서, 기본방정식으로 연속방정식, 운동방정식을 세우고. 에너지와 운동량 전달 메카니즘 사이에 유사성이 존재한다고 가정하였으며, 전단응력의 크기는 필자의 모델을 적용하였다. 기본방정식을 기체 속도, 액체 속도, 필름의 두께, 압력에 대해서 수치해를 구하여서 동일조건 하에서 실험한 데이터와 비교하였다. 수증기와 액체 경계면에서의 전단응력은 매우 좋은 일치를 보여주고 있다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.6
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• pp.1487-1493
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• 2008

In order to investigate the cooling capacity of multi-heat pump applying an inverter compressor, the experiment on the cooling performance characteristics of heat pump with 3 indoor units was performed under the cooling standard and cooling low-temperature conditions. The system data were measured by the psychrometric calorimeter. The operation characteristics and the behavior of the cooling cycle of the heat pump with 3 indoor units were understood from the cooling capacity, COP, and P-h diagram by indoor-unit combination. The operating load and performance of the multi-heat pump depends on the indoor-unit combination. The cooling capacity and COP of the low temperature condition were larger than those of the standard one. Also the cycle was analyzed by using P-h diagram.

• Journal of the Korean Magnetics Society
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• v.10 no.1
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• pp.1-6
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• 2000

Amorphous Fe$_{79.7}$Si$_{9.3}$B$_{9.7}$Ni$_{1.4}$ ribbon alloys were fabricated by a single roll method. To enhance D. C. bias properties, the magnetic and micro-structural changes have been investigated as the variation of annealing time and condition. The D. C. bias properties were found to be directly related to micro-structural changes. Primary ${\alpha}$-Fe dendrites with 200∼300 nm showed the best D. C. bias properties, which resulted from the magnetic domain wall pinning effect. Due to the differences of cooling rate, the growth shape and distribution of the dendrites is divided into two areas.

• Journal of Energy Engineering
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• v.25 no.1
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• pp.69-75
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• 2016

Bubble size is a key parameter for an accurate prediction of bubble behaviours in the multi-dimensional two-phase flow. In the current STAR CCM+ CFD code, a mechanistic bubble size model $S{\gamma}$ is available for the prediction of bubble size in the flow channel. As another model, Yun model is developed based on DEBORA that is subcooled boiling data in high pressure. In this study, numerical simulation for the gas-liquid two-phase flow was conducted to validate and confirm the performance of $S{\gamma}$ model and Yun model, using the commercial CFD code STAR CCM+ ver. 10.02. For this, local bubble models was evaluated against the air-water data from DEDALE experiments (1995) and Hibiki et al. (2001) in the vertical pipe. All numerical results of $S{\gamma}$ model predicted reasonably the two-phase flow parameters and Yun model is needed to be improved for the prediction of air-water flow under low pressure condition.