• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 춘계 학술대회논문집
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• pp.79-84
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• 2005

The numerical solutions are examined on the effect of a centered heat conducting body on natural convection in a 2-D square cavity. The influences of the Rayleigh number, the dimensionless conducting body size, and the ratio of the thermal diffusivity of the body to that of the fluid have been investigated on the natural convection heat transfer in overall concerned region. The analysis reveals that the fluid flow and heat transfer processes are governed by all of them. Results for isotherms, vector plots and wall Nusselt numbers are reported for Pr = 0.71 and relatively wide ranges of the other parameters. Heat transfer across the cavity, in comparison to that in the absence of a body, are enhanced (reduced) in general by a body with a thermal diffusivity ratio less (greater) than unity. The heat transfer are also found to attain a minimum as the body size is increased.

• 한국항공우주학회지
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• 제44권12호
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• pp.1062-1070
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• 2016

본 연구에서는 전산해석을 통해 냉각 터빈 블레이드 팁 간극의 유동 및 열전달 특성을 연구하였다. 1단 고압터빈 노즐 출구에서 획득한 속도, 온도 프로파일을 로터의 입구에 적용하여 로터 도메인을 대상으로 전산해석을 하였다. 스퀼러 팁이 적용된 블레이드의 팁 간극을 스팬의 1%부터 2.5%로 조절하여 팁 간극의 공력 손실, 열전달 계수와 막냉각 효율의 영향을 고찰했다. 팁 간극이 커질수록 출구에서 공력 손실과 블레이드 끝단 표면에서 열전달 계수는 증가하였다. 특히 팁 간극이 스팬의 2%일 때 평균 열전달 계수가 급격히 증가하였다. 팁 영역의 막냉각 효율은 팁 간극이 작을수록 높았고, 캐비티 내부 냉각 홀 근처의 막냉각 효율이 높았다.

• 대한기계학회논문집B
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• 제33권1호
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• pp.17-27
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• 2009

Water jet impingement cooling is used to remove heat from high-temperature surfaces such as hot steel plates in the steel manufacturing process (thermo-mechanical cooling process; TMCP). In those processes, uniform cooling is the most critical factor to ensure high strength steel and good quality. In this study, experiments are performed to measure the heat transfer coefficient together with the inverse heat conduction problem (IHCP) analysis for a plate cooled by planar water jet. In the inverse heat transfer analysis, spatial and temporal variations of heat transfer coefficient, with no information regarding its functional form, are determined by employing the conjugate gradient method with an adjoint problem. To estimate the two dimensional distribution of heat transfer coefficient and heat flux for planar waterjet cooling, eight thermo-couple are installed inside the plate. The results show that heat transfer coefficient is approximately uniform in the span-wise direction in the early stage of cooling. In the later stage where the forced-convection effect is important, the heat transfer coefficient becomes larger in the edge region. The surface temperature vs. heat flux characteristics are also investigated for the entire boiling regimes. In addition, the heat transfer rate for the two different plate geometries are compared at the same Reynolds number.

• 설비공학논문집
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• 제5권4호
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• pp.265-277
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• 1993

Recently, underground transmission system is growing continuously according to the electric power demand increase in the downtown area. Even if domestic cable makers are manufacturing 154kV oil filled cable and joint, the design technology of cable-joint has not been fully self-reliance. This study is aimed at the detail heat transfer analysis of 154kV cable-joint. So, that is cut into the five sections in order to analyze a conjugate natural convection in two dimensional $r-{\theta}$ coordinate. The streamline and temperature distributions are obtained for each sections. Also the changes of those are analyzed with respect to the variation of transmission currents and cable-joint surface heat transfer coefficients. The same analyses are also shown in view point of the maximum temperature of conductor and local equivalent conductivity.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.121-125
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• 2008

In this study, the characteristics of internal flow and the heat transfer performance of dimpled plate heat exchanger were numerically investigated. For the numerical analysis, conjugate heat transfer method between cold fluid - plate - hot fluid was studied with appropriate boundary conditions. Velocity magnitude, temperature and pressure distribution were obtained from the simulation. Correlations for fanning f-factor and Colburn j-factor were obtained from numerical results and compared to the experimented data.

• International Journal of Aeronautical and Space Sciences
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• 제18권2호
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• pp.279-289
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• 2017

In this study, a series of conjugate heat transfer (CHT) analyses are conducted for a stage of a fully cooled high-pressure turbine (HPT) at elevated levels of free stream turbulence (Tu = 5% and 25.7%). The goal of the analyses is to investigate the influence of high turbulence intensity on the fluid-thermal characteristics of a nozzle guide vane (NGV). The turbine inlet temperature is defined by considering a typical radial temperature distribution factor (RTDF). The Unsteady Reynolds Average Navier-Stokes (URANS) CHT simulations are carried out using CFX 15.0, a commercial CFD package. The presented CFD modeling approach for high turbulence intensity is verified with the experimental data from two types of NASA C3X NGVs with films. The computation grid is generated for both the fluid and solid domains. The fluid domain grid is created using a tetrahedral grid system with prism layers because of its complex geometry, and the solid domain grid is composed of only tetrahedral elements. The analytical results are compared to understand the effect of turbulence on flow characteristics and metal temperature distributions. The results obtained in this study provide useful insights on the effects of high free stream turbulence and unsteadiness. The results also lead to the proposal of meaningful turbine design guidelines.

• 오토저널
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• 제9권4호
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• pp.69-76
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• 1987

A conjugate conduction-convection analysis has been made for a plate fin which exchanges heat with its fluid environment by forced convection. The analysis is based on a one- dimensional model for the plate fin whereby the transient heat conduction equation for the fin is solved simultaneously with the conservation equations for mass, momentum, and energy in the fluid boundary layer adjacent to the fin. The forced convection heat transfer coefficient is not specified in advance but is one the results of the numerical solutions. Numerical results of the overall heat transfer rate, the local heat transfer coefficient, the local heat flux, the fin efficiency and the fin surface temperature distribution for Pr=0.7 are presented for a wide range of operating conditions.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.194-198
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• 2006

In this study, numerical modeling was performed to analyze air flow including radiation heat transfer inside a small chamber. Characteristics of heat transfer between source plate and target through glass are investigated for various surface temperature of heat source plate with buoyancy effect due to gravity force. Conduction heat transfer through the glass is considered and heat source plate is assumed to be a black body. Target surface temperature is largely affected by the radiation heat transfer. It can also be seen that as the source temperature increases target surface is dominated by radiation rather than convective heat transfer by air.

• 한국전산유체공학회지
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• 제21권1호
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• pp.1-9
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• 2016

Atmospheric icing may have significant effects not only on safety of aircraft in air, but also on performance of wind turbine and power networks on ground. Thus, ice protection measure should be developed to protect these systems from icing hazards. A very efficient method is the electro-thermal de-icing based on a process by which ice accretion is melted and blown away through aerodynamic forces. In this computational study, a state-of-the-art icing code, FENSAP-ICE, was used for the analysis of electro thermal de-icing system. Computational results including detailed conjugate heat transfer analysis were then validated with experimental data. Further, the computational model was applied to the DU21 airfoil section of NREL 5MW wind turbine with calculated heater parameters.

• 한국항공우주학회지
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• 제38권4호
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• pp.395-402
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• 2010

배플 분사기는 연소실 안으로 돌출되어 횡 방향 모드로 발생하는 고주파 연소불안정을 억제하는 배플을 형성한다. 고온의 연소가스에 노출되기 때문에 배플 분사기는 케로신 유로를 통해 자체 냉각이 가능하도록 설계한다. 20개의 나선형 냉각 채널을 갖는 배플 분사기가 개발되어 30톤급 연소기에 성공적으로 적용되어 왔으며, 별도의 외부 냉각을 필요로 하는 내열재 배플이 갖던 성능 감소 문제를 해결하였다. 본 연구는 케로신 냉각유로의 설계를 개선함으로서, 냉각 성능을 만족하는 범위 내에서 제작성을 향상시켜 연소기 대형화로 인해 증가하는 배플 분사기의 제작 비용을 절감하는 데 목적을 두었다. 이를 위해 배플 분사기에 대한 복합열전달 해석을 수행하였으며, 설계 수정된 배플 분사기는 75톤급 실물형 연소기에 적용하기 전에 축소형 연소기의 연소시험을 통해 열 내구성을 검증하였다.