• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1997년도 추계 학술대회논문집
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• pp.120-125
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• 1997

In the present work the influence of various physical parameters on the two-phase flow behavior in a self-heated porous medium has been studied using a numerical model, that is, the effects of heat generation rate, of porosity, of particle size, and of system pressure on the dryout process. To analyze the effect of these parameters, the variation of both liquid volumetric fraction (i.e., liquid saturation) and liquid axial velocity is evaluated at the steady state or at the onset of a first boiled-out region. The analysis of computational results indicate that a qualitative tendency exists between the parameters such as heat generation rate, porosity, effective particle diameter and the temporal development of the liquid volumetric fraction field up to dryout. In addition to these parameters, a variation of fluid properties such as phase density, phase viscosity due to a change of system pressure can be used for gaining insight into the nature of two-phase flow behavior up to dryout.

• 한국화재소방학회논문지
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• 제12권2호
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• pp.61-68
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• 1998

가축사료 분진의 열적 안정성 실험결과 본 연구에서 사용한 시료 입도의 경우 발열개시온도 및 발열 량에는 별 차이가 없었으나, 숭온속도가 충가함에 따라 발열개시온도가 낮아지고, 입도가 미세해질수 록 분해열이 증가함을 알 수 있었다. 한편, 분위기 기체룰 조연성 기체인 Oz로 사용할 경우 불활성 기 체인 Nz를 사용하는 경우보다 발열개시온도는 현저히 낮아지며, 반면에 발열량도 20배 이상 중가하였 다. 또한 본 연구에서 사용한 시료중 비교적 미세업자가 대기중에 부유하기 쉽고, 외부에서 점화에너지 가 주어질 경우 공기중의 산소와 쉽게 순간적으로 반용하여 폭발하는 것올 볼 수 있다. 본 연구에서의 시료입도중 80/100 mesh의 경우 평균 최대폭발압력은 6.88 Kgf / cm2 로 구해졌다.

• 연구논문집
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• 통권28호
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• pp.137-143
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• 1998

In the case of a boiler, scale is made in the tube by the chemical reactions of Ca and Mg ions contained in the water, and heat transfer rate is reduced because of increasement of heat resistance in the pipe of the heat flow. Thus it brings to reduce the energy efficiency and to make environmental pollution by the use of chemicals for the prevention and removement of scale. In this paper, we discussed the design of electronic generator for dual ultrasonic transmitters and analyzed the effect of scale prevention by ultrasound.

• 설비공학논문집
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• 제10권4호
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• pp.440-448
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• 1998

This paper considers the influence of circumferential wall heat conduction for the case of forced convection around a circular cylinder in cross flow of air. Keeping uniform heat generation from the inner surface of the cylinder in radial direction, heat is transferred by wall conduction in the circumferential direction due to the asymmetric nature of the temperature distribution of the cylinder and by convection around the perimeter of the cylinder. The wall conduction depends on conductivity of the cylinder and size of the cylinder radius and thickness and affects the local convective heat transfer rate significantly for geometrically similar surfaces and flow conditions. A nondimensional conjugation parameter K. (=k$_t$R/k$_w$b) has been used to characterize the effect of the circumferntial wall heat conduction. The small values of conjugation parameter K are found to be associated with large effect of wall conduction on the local convective heat transfer rate.

• 한국식품과학회지
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• 제20권3호
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• pp.303-309
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• 1988

Extruder 조작조건에 따른 extruder 내부물질의 온도변화는 제품의 물리화학적인 특성에 큰 영향을 미치는 요소이다. 자가발열형 single screw extruder를 사용하여 원료의 종류, 입자크기 수분함량과 같은 사입원료 조건과 사출구의 형태, breaker의 형태등과 같은 extruder의 구조적인 요소 및 냉각방법과 스크류 회전속도와 같은 작동조건을 달리했을 때의 작동초기 단계에서 열발생 속도와 평형상태에서 내부온도 분포를 관찰하였다. 쌀가루, 보리가루, 밀가루, 탈지대두분을 원료로 하여 각각 압출성형했을 때 바렐내부 발열상태를 보면 탈지대두분이 가장 급격한 온도증가를 나타내었으며 쌀가루가 가장 낮게 나타났다. 수분함량이 감소함에 따라 각 부위 온도 및 동력요구량은 증가했고, 입자크기가 작을 수록 표면적이 증가하여 압축부위 온도가 높았다. 스크류 회전속도가 증가함에 따라 각 부위의 온도가 높아졌다. 또한 바렐내부 온도분포가 계량부위>사출구부위>압축 부위 순서로 이루어질 때 extruder 작동상태가 가장 양호하였다.

• 환경위생공학
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• 제14권4호
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• pp.93-98
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• 1999

We had investigated combustion properties of rice bran dusts. Decomposition of rice bran dusts with temperature were investigated using DSC and the weight loss according to temperature using TGA in order to find the thermal hazard of rice bran dusts, and the properties of dust explosion in variation of their dust with the same particle size. Using Hartman's dust explosion apparatus which estimate dust explosion by electric ignition after making dust disperse by compressed air, dust explosion experiments have been conducted by varying concentration and size of rice bran dust.According to the results for thermodynamic stability of rice bran dust, there are little change of initiation temperature of heat generation and heating value for used particle size. But initiation temperature of heat generation decreased with high heating rate whereas decomposition heat increased with particle size. Average maximum explosion pressure was $10kgf/cm^2$ for 60/70 mesh and $1.5mg/cm^2$ dust concentration.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.228-233
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• 2000

The Korean Next Generation Reactor(KNGR) is a Pressurized Water Reactor adopting direct vessel injection(DVI) to optimize the performance of emergency core cooling system(ECCS). In a certain accident, however, pressurized thermal shock(PTS) of the vessel due to the sudden contact with the injected cold water is expected. In this paper, an accident of Main Steam Line Break(MSLB) has been numerically investigated with direct vessel injections and an increased volume flow rate in some cold legs. Using FLUENT code, temperature distributions of the fluid in the downcomer and of reactor vessel including the core region have been calculated, together with the distribution of convective heat transfer coefficient(CHTC) at the cladding surface of the reactor vessel. The result shows that some parts of the core region of the reactor vessel have higher temperature gradient expressing higher thermal stress.

• 한국초전도ㆍ저온공학회논문지
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• 제1권1호
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• pp.48-55
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• 1999

thermodynamic cycle analysis has been performed for the power generation systems to utilize the cold energy of liquefied natural gas (LNG). The power cycle used the air or water at room temperature as a heat source and the LNG at cryogenic temperature as a heat sink. Among manypossible configurations of the cycle. the open Rankine cycle. and the closed Brayton cycle, and the closed Rankine cycle are selected for the basic analysis because of their practical importance. The power output per unit mass of LNG has been analytically calculated for various design parameters such as the pressure ratio. the mass flow rate. the adiabatic efficiency. the heat exchanger effectiveness. or the working fluid. The optimal conditions for the parameters are presented to maximize the power output and the design considerations are discussed. It is concluded that the open Rankine cycle is the most recormmendable both in thermodynamic efficency and in practice.

• Nuclear Engineering and Technology
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• 제52권12호
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• pp.2771-2788
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• 2020

Experiments are conducted to study bubble flow behavior during the instability of subcooled boiling under uniform and non-uniform transverse heating. The non-uniform heat distribution introduces nonuniform bubble generation and condensation rates on the heated surface, which is different from the uniform heating. These bubble generation and condensation characteristics introduce a non-uniform local pressure distribution in the transverse direction, which creates an extra non-uniform pressure on the flowing bubbles. Therefore, different bubble flow behavior can be observed between uniform and non-uniform heating conditions. In the uniform heating, bubble velocity fluctuations are low, and the bubbles travel straight along the axial direction. In the non-uniform heating, more fluctuation in the bubble velocity occurs at low mass flow rate and high subcooled inlet temperatures, and reverse flow is observed. Additionally, the bubbles show a zigzag trajectory when they pass through the channel, which indicates the existence of cross flow in the transverse direction.

• 한국태양에너지학회 논문집
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• 제34권3호
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• pp.57-65
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• 2014

As the environmental regulations is more strengthened, the study of the renewable energy system and waste heat for electricity production is being accelerated. In this study, the performance and power generation rate of solar power generation by using R134a Rankine cycle was analyzed with solar radiation and mass flow rate of R134a. As a result, the maximum and minimum collected heat of solar collector was 20.4 kW and 13.6 kW at October and December, respectively. Besides, the highest generator power was generated at October and it was 0.91 kW/day, while the lowest generator power is occurred at December and it was about 0.85 kW/day.