• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1147-1152
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• 2009

The objectives of this paper are to study the characteristics of heat transfer and pressure drop of the zigzag channel PCHE using diffusion bonding technology by numerical analysis. PCHE of five types are designed, which are zigzag channel angle $180^{\circ}$, $160^{\circ}$, $140^{\circ}$, $120^{\circ}$ and $100^{\circ}$. The zigzag PCHE was numerically investigated for Reynolds number in a range of $150{\sim}800$. The temperatures of the hot side were performed at $80^{\circ}C$ while that of the cold side was conducted at $20^{\circ}C$. The results show that the performance of heat transfer rate for zigzag channel $100^{\circ}$ increases about 11.5% compared to that of zigzag channel $180^{\circ}$. On the other hand, the performance of pressure drop for zigzag channel $100^{\circ}$ is remarkably higher than that of zigzag channel $180^{\circ}$, about 1.4 times.

• 전기학회논문지
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• 제65권6호
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• pp.1007-1012
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• 2016

Induction motors are used widely in driving load of a fluid, such as a pump or a fan in the industry. Induction motor has been generated the voltage drop by the occurrence of a high current during startup. In addition, high start-up current can act as a mechanical stress on the shaft of the motor. So there is need a way to reduce the starting current. Soft start method is one of the many ways to reduce the starting current. This method uses silicon-controlled rectifiers(SCRs) for varying value of the voltage applied to the motor. There is a case for fixing or changing the thyristor firing angle to adjust the magnitude of the voltage. Starting power factor of induction motor is very low compared to the normal operation. Soft starting with the firing angle fixed needs to be considered a low power factor at startup. In this study, we compared the direct start characteristics and soft start characteristics considering the low power factor at the time of start-up. It was possible to confirm that the starting current and the voltage drop is present differently according to the firing angle.

• 한국항공우주학회지
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• 제40권7호
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• pp.601-607
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• 2012

착륙장치는 완충장치를 이용하여 항공기 착륙 시의 충격을 흡수하는 역할을 한다. 군용 헬기를 비롯한 일부 항공기에서는 비상 착륙시 탑승원의 생존성과 안전성을 향상시키기 위해, 착륙장치에 내추락 요구조건을 부여하기도 한다. 이 논문에서는 관련 규정에서 요구하고 있는 내추락 요구조건을 충족하는 착륙장치 설계 개념을 제시하고, 성능해석 및 낙하시험을 통한 입증 과정을 소개한다. 추락 시 착륙장치 충격흡수 능력과 거동은 낙하시험 시 측정한 다양한 센서 데이터 및 고속 카메라로 촬영한 동영상 분석을 통해 확인할 수 있다.

• 한국표면공학회지
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• 제41권2호
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• pp.63-68
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• 2008

Traditionally and generally used calcined clay was carburized, and its characteristics were studied. Carburization treatment was performed by the thermally decomposed carbon and the deposit carbon which occur in a so called 'Boudouard reaction $(2CO{\rightarrow}CO_2+C)'$ at fuel combustion process in a closed-type furnace. The color of the carburized calcine clay changed from yellow to black, and the carbon component revealed as crystalline graphite by the X-ray diffraction test. The weight of the carburized calcine clay decreased to about 4 wt.% by the 1st heating to $1400^{\circ}C$ in air but it does not decreased by the 2nd heating of the same conditions. By the carburization treatment, the water absorption changed from 13 wt.% to 6 wt.%, and the contact angle for water drop changed, too, from 0 to $87^{\circ}$ which was tested by the photograph of one minute after a water drop contact. It means the carburized calcine clay does not absorb water drop so it has a hydrophobic characteristic.

• 설비공학논문집
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• 제10권5호
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• pp.619-629
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• 1998

An experimental work was conducted to investigate a feasibility of simultaneous measurement of gas-liquid two-phase flowrates with double orifice plates using air and water. The tests were carried out under the atmospheric pressure and at the ambient temperature using two different tube sizes. Qualities of an air-water flow in the present study have values less than 0.1 and thus the mixed flow showed bubbly, plug, slug flow regimes. The probability density function (PDF) and the power spectral density function (PSDF) of the instantaneous pressure drop traces for the flow regimes were obtained. It is found that some distinctive features exist in the distribution of these functions, depending upon the two-phase flow pattern. The time-averaged value of the instantaneous pressure drop increases with increasing gas and liquid flowrates, showing a single-valued function for the total mass flowrate and the quality. It is also found that the two-phase discharge coefficient exhibits a consistent trend for variation of dimensionless parameters such as the superficial velocity ratio and the gas Reynolds number. The results indicate that simultaneous measurement of two-phase flowrate may be possible based upon a statistical analysis of the instantaneous pressure drop curves monitored using double orifice plates.

• 설비공학논문집
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• 제7권4호
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• pp.589-599
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• 1995

The frictional pressure drop of a capillary tube flow is experimentally investigated for pure refrigerants such as R32, R125, and R134a and refrigerant mixtures such as R32/R134a(30/70 by mass percent), R32/R125(60/40), R125/R134a(30/70), and R32/R125/R134a(23/25/52). The binary interaction parameters for the calculation of viscosities of refrigerant mixtures are found based upon the data in the open literature. Several homogeneous flow models predicting the viscosity of two-phase region are compared to select the best model. Cicchitti's equation is known to be the most adequate for the prediction of the viscosity for refrigerant mixtures, which is used in the analysis of adiabatic capillary flows. A model for the prediction of the frictional pressure drop of single and two-phase flow is developed for refrigerant mixtures in this study. This model may be used to design and analyze the performance of a capillary tube in the refrigerating system.

• 설비공학논문집
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• 제21권9호
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• pp.475-482
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• 2009

The objectives of this paper are to study the characteristics of heat transfer and pressure drop of the zigzag channel PCHE using diffusion bonding technology by numerical analysis. PCHE of five types are designed, which are zigzag channel angle 180$^{\circ}$, 160$^{\circ}$, 140$^{\circ}$, 120$^{\circ}$ and 100$^{\circ}$. The zigzag PCHE was numerically investigated for Reynolds number in a range of 150$\sim$800. The temperatures of the hot side were performed at 80$^{\circ}$ while that of the cold side was conducted at 20$^{\circ}C$. The results show that the performance of heat transfer rate for zigzag channel 100$^{\circ}$ increases about 11.5% compared to that of zigzag channel 180$^{\circ}$. On the other hand, the performance of pressure drop for zigzag channel 100$^{\circ}$ is remarkably higher than that of zigzag channel 180$^{\circ}$, about 2.4 times.

• Korean Journal of Chemical Engineering
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• 제35권11호
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• pp.2321-2326
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• 2018

We evaluated the optimal conditions for fluidization of nickel oxide (NiO) and its reduction into high-purity Ni during hydrogen reduction in a laboratory-scale fluidized bed reactor. A comparative study was performed through structural shape analysis using scanning electron microscopy (SEM); variance in pressure drop, minimum fluidization velocity, terminal velocity, reduction rate, and mass loss were assessed at temperatures ranging from 400 to $600^{\circ}C$ and at 20, 40, and 60 min in reaction time. We estimated the sample weight with most active fluidization to be 200 g based on the bed diameter of the fluidized bed reactor and height of the stocked material. The optimal conditions for NiO hydrogen reduction were found to be height of sample H to the internal fluidized bed reactor diameter D was H/D=1, reaction temperature of $550^{\circ}C$, reaction time of 60 min, superficial gas velocity of 0.011 m/s, and pressure drop of 77 Pa during fluidization. We determined the best operating conditions for the NiO hydrogen reduction process based on these findings.

• Nuclear Engineering and Technology
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• 제54권3호
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• pp.1098-1108
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• 2022

The effect of the material hardening model of the canister on a finite element vertical cask drop simulation is investigated for the strain-based acceptance evaluation. Three different hardening models are considered in this paper: the isotropic hardening model, the strain rate-dependent Johnson-Cook (J-C) hardening model, and the modified J-C model which are believed to be the most accurate. By comparing the results using the modified J-C model, it is found that the use of the J-C model provides similar or larger stresses and strains depending on the magnitudes of the strain and strain rate. The use of the isotropic hardening model always yields larger stresses and strains. For the strain-based acceptance evaluation, the use of the isotropic hardening model can produce highly conservative assessment results. The use of the J-C model, however, produces satisfactory results.

• 한국시뮬레이션학회논문지
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• 제18권3호
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• pp.91-102
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• 2009

평균 윈도우 크기는 평균 처리율과 많은 관계를 가지고 있다. 제안된 dropper는 fairness를 향상시키기 위해 윈도우 크기를 각 플로우의 레벨에 맞게 제어하도록 한다. 경쟁 패킷 드랍은 플로우가 많은 양의 대역폭을 차지하기 위해 동작한다. 경쟁 패킷 드랍 때문에 플로우는 전송 속도를 반으로 줄이게 되며, 이에 따라 코어 링크의 여유 용량이 존재하게 된다. 다른 플로우는 이 새로운 용량을 사용하게 되고, 따라서 다른 플로우는 좋은 처리율을 가지게 된다. 이런 방식으로 TCP의 전송속도를 제어하는 edge router의 새로운 기능 block인 TRC Dropper(Transmission Rate Control Dropper)를 제안한다. 제안한 TRC Dropper를 통하여 플로우들 간에 공평한 대역폭 분배를 실현하여 상대적으로 차별화된 서비스를 제공할 수 있다.