• Nuclear Engineering and Technology
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• 제38권3호
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• pp.251-258
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• 2006

This study presents an idea of using analogy concept to the heat transfer studies regarding the HTGR development. Theoretical backgrounds regarding the idea were reviewed. In order to investigate the predictability of a mass transfer system for heat transfer system phenomenology, an electroplating system coupled with a limiting current technique was adopted. Test facilities for laminar forced convection and natural convections under laminar and turbulent conditions were constructed, for which heat transfer correlations are known. The test results showed a close agreement between mass transfer and heat transfer systems, which is an encouraging indication of the validity of the analogy theory and the experimental methodology adopted. This paper shows the potential of the experimental method that validates the little-understood heat transfer phenomena, even in complex geometries such as HTGR.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.145-148
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• 2003

Thermal characteristics according to the bearing preload arc studied for the four type spindles with high frequency motor. For the analysis. three dimensional models are built considering heat transfer characteristics such as natural and forced convection coefficients, Bearing and motor are main heat generation, and heat generation by ball bearings as a function of load. viscosity and gyroscopic moment effect are considered. Unsteady-state temperature distributions and thermal displacements according to the bearing preload are analyzed by using the finite clement method.

• 대한설비공학회지:설비저널
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• 제11권2호
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• pp.10-15
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• 1982

An experimental study on the storage tank which uses sensible heat of water is done. The influence of inlet flow rate (Re), the difference between initial temperature and inlet water temperature(Gr) and the location of inlet and outlet on the performance of storage tank is studied. Development of stratification is examined by measuring the transient temperatures of 36 points inside the tank. Measured values are transformed to the dimensionless parameters in order to calculate the temperature efficiency of storage tank. In the presence of combined natural and forced convection, the development of stratification becomes clearer and thus the efficiency becomes higher, as $Gr/Re^2$ increases.

• 한국정밀공학회지
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• 제19권8호
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• pp.92-99
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• 2002

This work investigated the optimal condition for an uniform deposition growth rate in the vertical cylindric CVD chamber. Heat transfer, surface chemical reaction and mass diffusion in the flow field of CVD chamber h,id been computed using Fluent v5.3 code. A SIMPLE based finite Volume Method (FVM) was adopted to solve the fully elliptic equations for momentum, temperature and concentration of a chemical species. The numerical analysis results show good agreements with the measurements obtained by N. Yoshikawa. The results obtained by the numerical analysis showed that the film growth rate in the center of a susceptor is increasing, as the inner flow approaches to the forced convection. To the contrast, as it approaches to the natural convection, that in the outside of a susceptor is increasing. As the Reynolds number increases, the uniformity may not hold due to the larger temperature gradient at a susceptor surface. Therefore, when the temperature gradient on the surface of a susceptor is zero, the film growth rate becomes uniform on most surface.

• 대한기계학회논문집B
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• 제41권10호
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• pp.693-698
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• 2017

원통형 리튬이온 배터리를 이용한 배터리 팩의 냉각을 위한 해석을 수행하였다. 파우치형에 비해서 원통형 셀을 이용한 배터리 팩은 저렴하면서 신뢰도가 우수한 것으로 알려져 있다. 단지 부피가 파우치 타입에 비해서 크고 디자인적으로 제약이 있다라는 단점을 가지고 있다. 본 논문에서는 18650 배터리를 이용한 배터리팩의 냉각성능을 해석을 통하여 예측하였다. 배터리팩의 온도 안정성은 자동차용 배터리 팩에서 가장 중요한 부분이기 때문이다. 해석을 수행하기 전에 발열 시험을 수행하였으며 열화상 카메라를 이용하여 온도를 측정하고 해석을 통해서 이에 해당하는 발열량 값을 예측하였다. 이를 바탕으로 배터리 팩의 자연대류와 강제대류 해석을 진행하였으며 각각의 냉각 성능을 비교하였다. 배터리 셀을 직접 냉각하는 직접냉각 방식, 배터리 케이스 상하면을 냉각하는 방식, 배터리 케이스 상하면에 공기 통로를 설치하는 세 가지 방식에 대해서 냉각 성능을 비교하였고, 공기채널 방식이 안정성과 냉각성능 면에서 우수함을 해석을 통하여 입증하였다.

• 한국전산유체공학회지
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• 제20권1호
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• pp.65-76
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• 2015

In this study, the natural convection phenomenon of the air side and the forced convection phenomenon of the oil side were simulated in the radiator through a 3-D numerical analysis, and the total heat released by the oil side into the radiator heating plate and then to the air side was evaluated. Also, a quantitative analysis was carried out on the effect of each thermal resistance on the overall heat transfer coefficient through a 1-D thermal circuit analysis on the heat transfer mechanisms of the radiators considered in this study. In addition, for the diverse shapes of the heating plates considered in this study, the pressure drops of the oil side were quantitatively compared and evaluated. The temperatures at the air side and the oil side outlets of the radiators with 8 different fin shapes considered in this study had almost similar values showing a difference of +/-3% and, accordingly, the total heat transfer also showed similar heat dissipation performance in all the models. As a result of the 1-D thermal circuit analysis, in all the models considered in this study, while the thermal resistance of the air side accounted for 92% to 96% of the total, that of the oil side was 5 to 7%, and that of the heating plate showed a very small value of 0.02%.

• 한국전자통신학회논문지
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• 제19권3호
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• pp.589-602
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• 2024

열전 발전기(TEG)는 일반적으로 열 변환 효율이 높지 않다. 열전 발전기 모듈의 성능은 재료의 특성, 다리의 개수 외에도 다리의 형상에 따라 달라진다. 본 연구에서는 폐열을 효율적으로 수확할 수 있도록 열전소자의 다리 형상을 원통형, 큐브형 등 다양한 기하학적 구조로 모델링하여 전기적 특성을 수치상으로 비교하였다. 다리 형상에 따른 온도분포 및 발전량을 비교하였고 기존 Cube 모양이 가장 높게 나타났다. 냉각효과를 적용한 발전량을 비교한 결과 자연대류에서는 Cone, 강제대류에서는 Hourglass 모양이 가장 높았다. 본 연구 결과에 따르면 기하학적 구조가 열전 발전기의 효율에 영향을 미칠 수 있음을 확인하였다

• 태양에너지
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• 제20권3호
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• pp.39-50
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• 2000

Radiant barrier systems(RES) constructed with low emissivity materials bounded by an open air space can be used to reduce the net radiation transfer between two surfaces. To analyze the heat transfer characteristics of the radiant barrier systems which consist of a single-glass and radiation barriers, a simple theoretical model based on energy balances was suggested. And the model was validated by means of the experimental results. Using a guarded hot box, the temperatures of layers in selected RES and energy use for each cases were measured. The results show that the model well explained the heat transfer characteristics of those RES. Also, the heat transfer coefficient correlations considering natural and forced convection heat transfer ware suggested. It is found that the heat transfer efficiency of a RBS with aluminium surface improved up to 66.6% over that of a single glazing system.

• 대한설비공학회지:설비저널
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• 제17권4호
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• pp.382-394
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• 1988

Dynamic characteristics of thermally-forced stratification process in a square enclosure with a linear temperature profile at the side walls have been investigated through flow visualization experiment and numerical analysis. The experiment was performed on air with the Rayleigh numbers of order $10^5$. A particle tracer method is used for the flow visualization and to obtain a sudden linear temperature profile at the side walls copper blocks which already have a linear temperature profile are come into contact with the thin copper plates of the test section. Immediately a meridional circulation is developed and heat transfer takes place from the wall to the interior region by circulation of fluid and finally a thermal stratification is achieved. In the numerical study, QUICK scheme for convective terms, SIMPLE algorithm for pressure correction, and the implicit method for the time marching are adopted for the integration of conservation equations. Comparison of flow visualization and numerical results shows that the developing flow patterns are very similar in dynamic nature even though there is a time lag due to the inevitable time delay in setting up a linear temperature profile. For high Rayleigh numbers, the oscillatory motion is likely to take place and stratified region is extended. However, initial temperature adjustment process is much slower than that for low Rayleigh numbers.

• 한국안전학회지
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• 제35권3호
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• pp.96-104
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• 2020

The numerical simulations were conducted to investigate the thermal-fluid phenomena occurred inside the experimental apparatus during a PCCS, used to remove heat released in accidents from a containment of light water nuclear power plant, operation. Numerical simulations of the flow and heat transfer caused by wall condensation inside the containment simulation vessel (CSV), which equipped with 18 vertical heat exchanger tubes, were conducted using the commercial computational fluid dynamics (CFD) software ANSYS-CFX. Shear stress transport (SST) and the wall condensation model were used for turbulence closure and wall condensation, respectively. The simulation using the actual size of the apparatus. However, rather than simulating the whole experimental apparatus in consideration of the experimental cases, calculation resources, and calculation time, the simulation model was prepared only in CSV. Selective simulation was conducted to verify the effects of non-condensable gas(NC gas) concentration, CSV internal pressure, and wall sub-cooling conditions. First, as a result of the internal flow of CSV, it was observed that downward flow due to condensation occurred surface of the vertical tube and upward flow occurred in the distant place. Natural convection occurred actively around the heat exchanger tube. Due to this rising and falling internal flow, natural circulation occurred actively around the heat exchanger tubes. Next, in order to check the performance of built-in condensation model using according to the non-condensable gas concentration, CSV internal flow and wall sub-cooling, the heat flux values were compared with the experimental results. On average, the results were underestimated with and error of about 25%. In addition, the influence of CSV internal pressure and wall sub-cooling was small, but when the condensate was highly generated due to the low non-condensable gas concentration, the error was large compared to the experimental values. This is considered to be due to the nature of the condensation model of the CFX code. However, in spite of the limitations of CFD, it is valid to use the built-in condensation model of CFD for PCCS performance prediction from a conservative perspective.