• 태양에너지
• /
• 제8권2호
• /
• pp.57-65
• /
• 1988

The coefficients of convective heat transfer were investigated when air is jetted to surface of the heated side-wall. The temperature on the side-wall was measured when the offsets changed from 1.5 to 10.5 as 7 steps at the state of fixed Reynolds numbers that were 35000, 29000 and 23000. The experimental results are as follows: 1. The mean Nusselt number is very high on the surface of reattached flow region. 2. The offset and the recirculation flow region decreased, while the mean Nusselt number increased between the outlet of nozzle and the region of reattachment flow. 3. The local Nusselt number is not concerned with Reynolds number on the recirculation flow and on the reattached flow region when the offset decrease. But the Nusselt number increased only when Reynolds numbers on the wall jet flow region increased. 4. The mean and the maximum Nusselt number decreases linearly, and in particular its values rapidly decrease in accordance with changing of the offset from 1.5 to 3 in inverse proportion.

• 대한기계학회논문집B
• /
• 제37권11호
• /
• pp.991-998
• /
• 2013

본 연구에서는 $6Ra=10^6$ 일 때, 사각 밀폐계 내부에 고온의 원형 실린더가 존재하는 자연대류에 대한 수치해석을 수행하였다. 밀폐계는 상부 벽면을 통해 냉각되고 양측 벽면과 고온의 국소 영역을 제외한 하부 벽면은 단열 조건이다. 하부 벽면에서 고온 영역이 차지하는 비를 w 로 정의 하였다. 반경이 밀폐계 한 변의 길이의 0.2 배인 원형 실린더를 구현하기 위해 유한체적법(FVM)에 기초한 가상 경계법(IBM)을 사용하였다. 본 연구에서는 w 가 고온의 원형 실린더를 갖는 밀폐계 내부의 자연대류에 미치는 영향을 $10^6$의 Rayleigh 수에 대해 2 차원 해를 구하였다. $10^6$의 Rayleigh 수에서는 유동장과 온도장은 시간에 따라 변하는 특성을 보였다.

• 에너지공학
• /
• 제21권3호
• /
• pp.254-264
• /
• 2012

원자력발전소 중대사고시 노심용융물의 Rayleigh-Benard 자연대류 문제에 대한 예비실험으로 두 평판 사이의 거리, 측면벽의 유무 및 평판의 기하구조가 열전달에 미치는 영향에 대해 실험적 연구를 수행하였다. 열전달 실험을 대신하여 상사성의 원리를 이용한 황산-황산구리 수용액의 전기도금계를 물질전달계로 채택하였다. 실험은 $Ra_s$는 $1.06{\times}10^7{\sim}2.91{\times}10^{10}$의 범위에서 실험적 조건을 변화시켜가며 열전달을 측정하였다. 실험결과 단일 수평평판에서 측정한 열전달은 McAdams의 수평평판 자연대류 열전달 상관식과 일치하였고 두 평판에서 측정한 열전달은 Dropkin과 Somerscales, Globe와 Dropkin의 Rayleigh-Benard 자연대류 열전달 상관식과 매우 유사한 경향을 보였다. 두 평판 사이의 거리가 작을 경우 열전달이 높다가 거리가 증가하면 단일 수평평판에서의 자연대류 열전달과 같아졌다. 평판에 설치된 휜(Fin)은 열전달을 향상시켰다. 모든 경우에서 측면벽이 없는 경우의 열전달이 측면 벽이 있는 경우보다 항상 높았다.

• 에너지공학
• /
• 제24권1호
• /
• pp.149-163
• /
• 2015

본 연구에서는 전산유체역학(Computational Fluid Dynamics, CFD) 해석코드를 사용하여 마스트집합체의 열수력적 안전성에 대한 연구를 수행하였다. 이를 위해 자연대류 벤치마크 문제를 선정하여 CFD 코드의 물리모델을 선정 및 해석 능력을 검증하고 이를 이용하여 마스트집합체에 대한 자연대류 열전달 해석을 수행하였다. 본 연구에서는 Betts et al.의 사각 수직공동에서 난류 자연대류 실험결과를 대상으로 CFD 해석을 수행하여 자연대류 조건에 적용하기 위한 난류 모델로 표준 $k-{\omega}$ 모델을 선정하였다. 이렇게 도출된 난류모델을 CFD코드에 적용하여 Bates et al.에 의해 수행된 PNL(Pacific Northwest Laboratory)의 $2{\times}6$ 번들 실험과 이에 대한 Kwon et al.의 MATRA, Fluent 코드의 해석과 비교 계산을 수행하여 CFD코드의 부수로조건 자연대류 열전달 해석 능력을 검증하였다. 최종적으로 도출된 $k-{\omega}$ 난류 모델을 사용하여 마스트집합체 및 핵연료 집합체에 대한 자연대류 해석을 수행하였다. 해석 결과 수조 내부 및 부수로 내에서 안정적인 자연대류 유동이 발생함을 확인하였으며, 본 유동 조건에서 핵비등이탈비를 계산함으로써 열수력적 안전성을 정량적으로 평가하였다.

• 한국자동차공학회논문집
• /
• 제14권6호
• /
• pp.151-159
• /
• 2006

A one-dimensional numerical analysis is carried out to investigate the effects of inlet gas humidities, inlet gas pressures, and thicknesses of membrane on the performance of a proton exchange membrane fuel cell. It is found that the relative humidity of inlet gases at anode and cathode sides has a significant effect on the fuel cell performance. Especially, the desirable fuel cell performance occurs at low relative humidity of the cathode side and at high humidity of the anode side. In addition, an increase in the pressure ranging from 1 atm to 4 atm at the cathode side results in a significant improvement in the fuel cell performance due to the convection effect by a pressure gradient toward the anode side, and with decreasing the thickness of membrane, the fuel cell performance is enhanced reasonably.

• Journal of Advanced Marine Engineering and Technology
• /
• 제24권2호
• /
• pp.17-23
• /
• 2000

Experimental investigations were conducted to study the forced convection of fully-developed turbulent flow in horizontal equilateral duct fabricated with the same length and equivalent diameter, but different surface roughness pitch ratio(P/e) of 4, 8 and 16 on the one side wall only. The experiments were performed with the hydraulic diameter based Reynolds number ranged from 70,000 to 10,000. The entire bottom wall of the duct was heated uniformly and the other surfaces were thermally insulated. To understand the mechanisms of the heat transfer enhancement, measurements of the heat transfer were done to investigate the contributive factor of heat transfer promotion, namely, the fin effect. And the results were compared with those of previous investigations for similarly configured channels, at which they were roughened by regularly spaced transverse ribs in the rectangular and circular channels.

• 한국전산유체공학회지
• /
• 제3권2호
• /
• pp.27-38
• /
• 1998

Rotating flow of a stratified fluid contained in a circular cylinder with unstable temperature gradient imposed on the side wall of it has been numerically studied. The temperatures at the endwall disks are constant. The top disk of the container is coider than that of the bottob disk, as much as the temperature difference n${\Delta}$T, (0${\leq}$n${\leq}$3). Flows in the vessel are driven by an impulsive rotation of the hot bottom disk with respect to the central axis of the cylinder. Flow details have been acquired. For this flow, the principal balance in the interior core is characterized by a relationship between the radial temperature gradient and the vertical shear in the azimuthal velocity. As the buoyancy effect becomes appreciable, larger portions of the meridional fluid transport are long-circuit from the bottom disk to the interior region via the side wall.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 춘계학술대회논문집B
• /
• pp.65-70
• /
• 2000

Experimental investigations were conducted to study the forced convection of fully-developed turbulent f)on· in horizontal equilateral duct fabricated with the same length and equivalent diameter, but different surface roughness Pitch ratio(P/e) of 4, 8 and 16 on the one side wall only The experiments were performed with the hydraulic diameter based Reynolds number ranged from 70.000 to 10,000 The entire bottom wall of the duct was heated uniformly and the other surfaces were thermally insulated. To understand the mechanisms of the heat transfer enhancement. measurements of the heat transfer were done to investigate the contributive factor of heat transfer promotion. namely the fin effect. And the results were compared with those of Previous investigations for similarly configured channels, at which they were roughened by regularly spaced transverse ribs in the rectangular and circular channels.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2006년도 하계학술발표대회 논문집
• /
• pp.627-632
• /
• 2006

An experimental study is conducted to investigate the effect of the tube row and fin spacing on the air-side heat transfer and friction characteristics of fin-tube heat exchangers with slit fin pattern. A total of twelve samples of fin-tube heat exchangers with the nominal tube diameter of 7 mm, transverse tube pitch of 19 mm and longitudinal tube pitch of 12.5 mm are tested. The thermal fluid measurements are made using a psychometric calorimeter. The raw data are reduced to the desired heat transfer coefficient in terms of j-factor and friction factor of f for various frontal air velocities, fin pitches and number of tube rows.

• Advances in materials Research
• /
• 제8권2호
• /
• pp.117-135
• /
• 2019

The lifetime of a gas turbine combustor is typically limited by the durability of its liner, the structure that encloses the high-temperature combustion products. The primary objective of the combustor thermal design process is to ensure that the liner temperatures do not exceed a maximum value set by material limits. Liner temperatures exceeding these limits hasten the onset of cracking which increase the frequency of unscheduled engine removals and cause the maintenance and repair costs of the engine to increase. Hot gas temperature prediction can be considered a preliminary step for combustor liner temperature prediction which can make a suitable view of combustion chamber conditions. In this study, the temperature distribution of ceramic panels for a V94.2 gas turbine combustor subjected to realistic operation conditions is presented using three-dimensional finite difference method. A simplified model of alumina ceramic is used to obtain the temperature distribution. The external thermal loads consist of convection and radiation heat transfers are considered that these loads are applied to flat segmented panel on hot side and forced convection cooling on the other side. First the temperatures of hot and cold sides of ceramic are calculated. Then, the thermal boundary conditions of all other ceramic sides are estimated by the field observations. Finally, the temperature distributions of ceramic panels for a V94.2 gas turbine combustor are computed by MATLAB software. The results show that the gas emissivity for diffusion mode is more than premix therefore the radiation heat flux and temperature will be more. The results of this work are validated by ANSYS and ABAQUS softwares. It is showed that there is a good agreement between all results.