• 설비공학논문집
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• 제17권11호
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• pp.1035-1042
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• 2005

In the present study, the principle of minimum energy is employed to configure the shape of rivulet flowing down an inclined surface. The profile of laminar rivulet is determined by numerical integration. The maximum center thickness, which corresponds to the minimum thickness of falling film, is found to exist regardless of liquid flow rate and is compared with the analytical and experimental data. At small liquid flow rate the center thickness of rivulet and its width increase almost linearly with flow rate. Once the center thickness of rivulet becomes very close to its maximum value, its growth rate retards abruptly. However the width of rivulet increases proportionally to the liquid flow rate and most part of its free surface is as flat as that of stable film. The growth rate of rivulet thickness with respect to liquid flow rate becomes larger at bigger contact angle. The width of rivulet increases rapidly with its flow rate especially at small contact angle, As the liquid-vapor interfacial shear stress increases, the center thickness of rivulet decreases with its flow rate, which is remarkable at small contact angle. However the effect of interfacial shear stress on the width of rivulet is almost negligible.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.175-180
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• 2001

In this study, the minimum heat flux conditions are experimentally investigated for the spray cooling of hot plate. The hot plates are cooled down from the initial temperature of about $900^{\circ}C$, and the local heat flux and surface temperatures are calculated from the measured temperature-time history. The results show that the minimum heat flux point temperatures increase linearly resulting from the propagation of wetting front with the increase of the distance from the stagnation point of spray flow. However, in the wall region, the minimum heat flux point temperature becomes independent of the distance. Also, the experimental results show that the velocity of wetting front increases with the increase of the droplet flow rate.

• 설비공학논문집
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• 제13권10호
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• pp.974-981
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• 2001

In this study, the minimum heat flux conditions are experimentally investigated for the spray cooling of hot plate. The hot plates are cooled down from the initial temperature of about$ 900^{\circ}C$, and the local heat flux and surface temperatures are calculated from the measured temperature-time history. The results show that the minimum heat flux point temperatures increase linearly resulting from the propagation of wetting front with the increase of the distance from the stagnation point of spray flow. However, in the wall region, the minimum heat flux point temperature becomes independent of the distance. Also, the velocity of wetting front increases with the increase of the droplet flow rate.

• Nuclear Engineering and Technology
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• 제51권4호
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• pp.1169-1175
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• 2019

The minimum detectable activity (MDA) value was derived according to the flow rate of the sample and degree of amplification of the device by sending the sample directly from the collection site to the detection part through a pump. This method can lead to reduction in time and cost compared to the existing measurement method that uses a pre-treatment process. In this study, experiments were conducted on $^3H$ and $^{90}Sr$, which are the major pure beta-emitting radionuclides, by setting the sample flow rate and the amplification gain as factors. The MDA values were derived according to the flow rates, considering that the flow rate can affect the MDA values. There were no change in the MDA under different flow rates of 0, 600, 800, and 1000 mL/min. Therefore, it was confirmed that the flow rate may not be considered when collecting samples for monitoring in actual field. As the degree of amplification of the amplifier increased, the time required to reach the target MDA decreased. When the amplification was quadrupled, the detection efficiency increased by approximately 23.4 times, and the time to reach the MDA decreased to approximately 1/550 times. This method offers the advantage of real-time on-site monitoring.

• 상하수도학회지
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• 제19권6호
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• pp.749-757
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• 2005

The present study analyzed actual cases of designed flow estimation method and designed flow rate of sewage pipe lines. In order to examine the effects of peak-hour demand factor estimation with given daily highest peak loading, we analyzed its effects on designed flow rate with changing the peak-hour demand factor from 2.0 to 10.0. The results of this study are as follows. When reviewing the recent designs, we found that 59.4% of pipe line with 250mm and 300mm diameter, which fall under minimum allowable pipeline did not meet the minimum velocity which is specified as 0.6m/sec in design standards. The pipe line that have minimal access population or have very low slope did not satisfy the minimum velocity. In estimating the designed sewage flow, the applied daily highest peak loading and hourly highest peaking loading were the load factor for the entire population of the planned area, and for the peak loading of the initial pipes connected to a very small population, we applied the same factor as that applied to the entire area and, as a result, the hourly highest flow was underestimated. Because, in case of the initial pipes, the method of applying the same peak loading to all subject areas is highly possible to produce underestimated design flow, when estimating the designed flow of the initial pipes connected to a small population need to adopt a rational flow factor according to the size of population. For this, it is considered to investigate and analyze raw data on daily and hourly variation of sewage flow.

• 한국산업융합학회 논문집
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• 제26권1호
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• pp.183-191
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• 2023

This study was conducted experimentally to investigate the surface temperature of the heat sink, the air temperature in the flow channel and the sample temperature by changing the channel number of channel type heat sink and the air flow rate when heating and cooling the bio sample. The target temperature of the sample was 15℃ or less as the minimum value and 82℃ or more as the maximum value. In this study, the channel number of the heat sink(N = 1, 2, 4, 5, 10) and the air flow rate(Q=25, 42, 54m³/min) were varied. The bio sample was replaced with water, and the volume of water is 4mL. The size of the heat sink is 80x73x150mm and the material is aluminum. When cooling the sample, the surface temperature, the air temperature and the sample temperature were highly dependent on the number of channels and the flow rate. However, when the sample is heated, the surface temperature, air temperature and sample temperature do not depend on the number of channels and the flow rate. It was found that the conditions for satisfying the minimum temperature of 15℃ or less when cooling the sample were the number of channels N≥5 and the flow rate Q≥42m³/min. When heating the sample, the conditions to satisfy the maximum temperature of 82℃ or more are the number of channels N≤5 and the air flow rate Q≤42m³/min.

• 한국전산유체공학회지
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• 제17권1호
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• pp.86-93
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• 2012

A numerical investigation is conducted to search for the optimal flow rate for a rotating-disk chemical vapor decomposition reactor operating at a high temperature and a low pressure. The flow of a gas mixture supplied into the reactor is modeled by a laminar flow of an ideal gas obeying the kinetic theory. The axisymmetric two-dimensional flow in the reactor is simulated by employing a CFD package FLUENT. With operating pressure and temperature fixed, numerical computations are performed by varying rotation rate and flow rate. Examination of the structures of flow and thermal fields leads to a flow regime diagram illustrating that there are a stable plug-like flow regime and a few unfavorable flow regimes induced by mass unbalance or buoyancy. The criterion for sustaining a plug-like flow regime is discussed based on a theoretical scaling argument. Interpretation of the flow regime map suggests that a favorable flow is attainable with a minimum flow rate at the smallest rotation rate guaranteeing the dominance of rotation effects over buoyancy.

• 터널과지하공간
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• 제24권2호
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• pp.176-186
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• 2014

절리면의 수리특성에 영향을 미치는 요소는 절리면의 거칠기, 절리면의 틈새, 충진물 등이 있다. 본 연구에서는 절리면의 거칠기에 따른 수리특성을 분석하고자 Barton and Choubey(1977)가 제안한 표준 프로파일을 이용하여 몬테카를로 시뮬레이션을 통해 인공 프로파일을 생성시켰다. 표준 프로파일과 인공 프로파일을 조합하여 유동채널 모델을 제작하였으며, 최소 간극의 변화와 유동채널의 형상에 따른 수리특성을 수치해석적으로 분석하였다. 두 프로파일이 이루는 최소 간극지점을 통과한 이후 유동면적이 증가하는 지점에서 최대 유동률을 나타냈으며, 최소 간극이 증가할수록 최대 유동률은 감소하였다. 또한 유동채널의 형상과 유동채널내의 최소 간극 지점의 위치가 모델마다 상이하기 때문에 단위면적당 최대 유동률은 모델마다 다른 값을 나타내고 있었다. 유동채널 내의 역학적 간극과 수리적 간극은 1.07 ~ 3.00 배 정도의 차이를 나타내고 있으며, 본 수리해석에서 분석된 $A_i$ 값과 역학적 간극은 $e_m=0.519A^{0.7169_i}$의 관계를 나타내고, 수리적 간극은 $e_h=0.6182A^{0.239}_i$의 관계를 나타는 것으로 분석되었다.

• 한국화재소방학회논문지
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• 제28권2호
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• pp.40-47
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• 2014

NFSC103의 배관스케줄방식으로 설계하는 경우, 작동면적 내의 헤드 약 50%가 최소요구량에 못미치는 문제점을 해결하기 위하여 NFSC103과 NFPA13의 배관스케줄방식을 비교, 분석하였으며 NFSC103의 유량부족 문제를 해결할 수 있는 새로운 방법을 제시하였다. 각 헤드에서의 소화수방출량을 기존의 80 L/min의 150%인 120 L/min으로 하면 수리계산한 값을 상회하여 모든 헤드에서 최소기준값인 1 bar, 80 L/min을 충족하게 된다. 이는 누구나 쉽게 배관스케줄방식으로 설계할 수 있으며 설계면적 내의 모든 헤드가 최소요구량을 충족하는 최적의 방법이다.

• Nuclear Engineering and Technology
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• 제8권4호
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• pp.203-207
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• 1976

질칼로이-4에 있어서 flow stress strain rate 의존성을 냉간가공 및 소둔된 시편에 대해 20$0^{\circ}C$-45$0^{\circ}C$ 온도 구간에서 응력이완 실험으로 조사하였다. 전체 실험온도에서 In-3-ln i 관계식은 $10^{-5}$-$10^{-3}$ sec$^{-1}$ strain rate의 구간에 걸쳐 선형관계를 보였다. 냉간 가공된 질칼로이 -4의 strain rate sensitivity, m값은 30$0^{\circ}C$에서 최소값을 보인 반면, 소둔된 시편의 경우 30$0^{\circ}C$와 45$0^{\circ}C$에서 최소값들을 보였다. 최소값의 m이 나타나는 온도는 가공시효값이 극대값을 보이는 온도와 일치한다는 사실이 확인되었다. m값의 감소는 활동자유전위들이 산소원자에 의해 pinning된 결과로 유발되는 가공 시효와 관련된 것으로 고려된다. 그리고 소둔된 시편이 45$0^{\circ}C$에서 가지는 최소 m값은 철 원자들로 인한 가공 시효에서 기인된 것으로 생각된다.