• Journal of Power System Engineering
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• v.10 no.1
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• pp.25-33
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• 2006

거칠기가 한 벽면과 두 벽면에 설치된 사각채널에서 비압축성 유체유동과 열전달을 조사하기위해 3차원 수치모사를 행하였다. CFX (version 5) software package 를 사용하여 계산하였다. 거친 벽은 $45^{\circ}$경사진 거칠기가 설치되어 있다. 채널의 4 벽면은 일정한 열 유속으로 가열하였다. 수치계산 결과는 실험값과 잘 일치 하였다. 연구의 조건은 거칠기 피치와 높이의 비가 8이고, 거칠기 높이와 채널 수력직경의 비가 0.067이며, 레이놀즈수의 범위는 7,600에서 24,900이었다. 연구의 결과는 열전달계수와 마찰계수는 사각채널에서 거친 벽면의 수가 클수록 증가 함을 보였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.11
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• pp.1073-1079
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• 2012

This study aims to experimentally investigate the heat transfer characteristics of a thermosyphon using nanofluids. A thermosyphon with three individual pipes, which share the internal volume of the evaporator section, was designed, and its performance was tested for various charge amounts, input powers of the evaporator section's heater, and concentrations of working fluids. The optimized charge amount of the thermosyphon using distilled water was 30%, and the thermal resistance of the thermosyphon with $TiO_2$ nanofluid was 18.1% lower than that with Ag nanofluid. In addition, the heat transfer performance of the thermosyphon with $TiO_2-1%$ was optimized at an input power of 300 W at the evaporator section's heater and a charge amount of 30%.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.1
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• pp.41-46
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• 1997

The change of flow field and the effects of convective heat transfer on the shape and location of melt/crystal interface has been studied during the crystal growth by the heat exchanger method. Although the thermal structure is stable in the crucible, the flow due to the natural convection driven by radial temperature gradient is significant, because the thermal stability is broken by the hemispherical melt/crystal interface shape. The maximum interface deflection with convection is smaller than without and the convective heat transfer should be considered to simulate the heat transfer process of heat exchanger method rigorously.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.5
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• pp.1-12
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• 2020

In this paper, the heat transfer characteristics of Jet A-1, which is used as a coolant and fuel in a regeneratively cooled thrust chamber, were experimentally studied. By varying the applied current for heating the cooling channel, the simulated specimen diameter, the specimen outlet pressure and the coolant flow rate, the wall temperatures of the specimen and the Jet A-1 temperatures at the specimen inlet/outlet were measured. It was found that the specimen diameter and the flow rate were important factors for the characteristics of heat transfer and the outlet pressure did not affect the performance of heat transfer. The results of the heat transfer experiments were compared with the previous Nusselt number empirical equations and novel Nusselt number empirical equations were finally derived.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05a
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• pp.584-589
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• 1998

범용 전산유체 해석코드인 CFX 4.1을 사용하여 철재격납용기 표면을 전열면으로 이용하는 피동격납용기냉각계통에 대한 열전달 현상해석을 수행하였다. 철재격납용기 내부와 외부 채널에서 발생하는 열전달 현상을 모사하기 위하여 액막의 유동 및 온도계산 모델을 범용 전산유체해석코드인 CFX4.1에 적용하여 철재격납용기 내.외부의 표면을 흐르는 액막의 높이, 액막내 온도분포, 철재격납용기 내.외부의 온도, 유속 및 부피분율 등을 계산하는 복합 열전달 해석 방법론을 개발하였다. 해석결과는 향후 실험 둥을 통한 검증이 필요하나 피동형 격납용기템각계통에서 발생하는 물리적 현상들의 복합적인 거동 분석에 사용될 수 있는 것으로 평가되었다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.2
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• pp.510-515
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• 2012

The objective of this study is to investigate low temperature performance characteristics of the thermosyphon with/without wick. Thermosyphons using water as the working fluid are tested with variations of wick, charge amount of the working fluid, outdoor temperature, and heat load for the evaporator section at a low temperature. As a result, the heat transfer of thermosyphon was optimized at the charge amount of 40% and increased with the rise of the outdoor temperatures.

• Journal of Energy Engineering
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• v.9 no.4
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• pp.309-318
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• 2000

핀-관 열교환기의 효율을 증대시키기 위하여는 열저항을 결정하는 데 있어서 중요한 역할을 하는 공기측 열전달 특성의 향상이 필요하다. 본 연구에서는 핀-관 열교환기의 공리측 성능을 해석하기 위해서 3차원 비압축성 Navier-Stokes 코드를 개발하였으며 이 코드는 시간항에 스칼라 내재적 근사분해법(scalar implicit approximate factorization)절차, 공간항에 유한체적법과 2차의 풍상차분법(upwind differencing)을 사용한다. 서로 다른 3개의 핀형상(평판핀, 슬릿핀, 파형핀)을 고려하였고 이들의 유동 및 열전달 특성을 연구하였다.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.827-830
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• 2002

A direct numerical simulation is performed for turbulent heat transfer in a concentric annulus at $Re_{Dh}=8900\;and\;Pr=0.71$ for two radius ratios ($R_{1}/R_{2}=0.1\;and\;0.5$) and $q^{\ast}=1.0$. Main emphasis is placed on the transverse curvature effect on near-wall turbulent thermal structures. Near-wall turbulent structures close to the inner and outer walls are scrutinized by computing the lower-order statistics. The fluctuating temperature variance and turbulent heat flux budgets are illustrated to confirm the results of the lower-order statistics. The present numerical results show that the turbulent structures near the outer wall are more activated than those near the inner wall, which may be attributed to the different vortex regeneration processes between the inner and outer walls.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.193-198
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• 2003

A gas turbine blade has an internal cooling passage equipped with ribs, which can be modeled as a ribbed channel. We have studied a flow inside a ribbed channel using large eddy simulaton (LES) with a dynamic subgrid-scale model. The simulation results are compared with the experimental ones. The turbulence intensity and local heat transfer near the rib have not been well captured by the conventional Reynolds averaged Navier-Stokes simulation (RANS). However, these variables obtained by the present LES agree well with those from experiments. From the instantaneous velocity and temperature fields, we explain the mechanisms responsible for the local peaks in the heat transfer distribution along the channel wall. We have also investigated the effect of rotation on the flow and heat transfer in the ribbed channel.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1436-1441
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• 2004

The internal cooling passage of a gas turbine blade can be modeled as a ribbed channel. Most studies have considered square ribs. However, the ribs can be rounded due to improper manufacturing or wear during the operation. Hence, we have studied two different rib geometries in this study, i.e. square and semicircle ribs. We have performed large eddy simulations (LES) and experiments to validate the results from the simulations. LES predicts the detailed flow and thermal features, which have not been captured by simulations using turbulence models. By investigating the instantaneous flow and thermal fields, we propose the mechanisms for the local heat transfer distribution between ribs. For both the geometries, heat transfer is enhanced by the entrainment of the cold fluid by the vortical motions and impingement of the entrained cold fluid on the ribs.