• 대한기계학회논문집B
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• 제21권4호
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• pp.551-561
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• 1997

Mixed convection of air in a horizontal concentric cylindrical annulus is investigated numerically. Isothermal boundary conditions are prescribed at the inner and outer cylinders, with the inner cylinder being warmer. The forced flow is induced by the outer cylinder which is rotating slowly with constant angular velocity with its axis at the center of the annulus. The effect of the forced flow on the flow pattern and heat transfer of natural convection is investigated for the annulus of (inner-cylinder radius/gap width) = 1. There appear two eddies, one eddy or no eddy according to the Rayleigh and Reynolds numbers. Map of the three flow regimes is constructed on the Ra-Re plane. (author). 28 refs., 9 figs., 2 tabs.

• 설비공학논문집
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• 제2권1호
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• pp.63-73
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• 1990

A numerical analysis of initial unsteady state flow and heat transfer in an enclosed cavity has been performed by the Modified QUICK Scheme. The stable QUICK Scheme which modified the coefficient always to be positive is included in this numerical analysis. The implicit method is applied to solve the unsteady state flow; between iterations the PISO (Pressure - Implicit with Splitting of Operators) algorithm is employed to correct and update the velocity and pressure fields on a staggered grid. The accuracy of the Modified QUICK Scheme is proved by applying fewer grid systems than those which Ghia et al. and Davis applied. The initial unsteady mixed convection in an enclosed cavity is analyzed using the above numerical procedure. This study focuses on the development of the large main vortex and secondary vortex in forced convection, the effects of the Rayleigh Number in natural convection and the relative direction of the forced and natural convection.

• 한국추진공학회지
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• 제13권1호
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• pp.51-57
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• 2009

이 연구 논문에서는 위상최적화 방법을 사용하여 강제대류를 이용한 열소산하는 구조물을 설계하는 방법을 개발한다. 전기 부품이나 기계구조물에서 발생하는 열을 낮추기 위해서 자연 대류와 강제 대류가 넓게 사용되고 있다. 또한 현재에는 화학전지(Fuel cell)나 로켓의 추진기관 등에서 발생한 열을 낮추기 위해서 강제 대류를 사용하고 있다. 현재에 이런 시스템을 효과적으로 열을 소산시키기 위해서 유동의 채널을 설계하는 것이 아주 중요한 이슈로 다루어지고 있다. 따라서 이 논문에서는 위상최적화 기법을 사용하여 최적의 채널을 설계하는 연구를 수행한다. 대류 현상을 고려하기 위해서 비압축성 N-S 방정식의 해석을 수행하였다. 이 논문에서는 열과 유체가 연계되어 있는 시스템을 수치적으로 연구하고 강제대류를 고려하는 최적의 채널 설계 결과를 제시한다.

• 한국식품과학회지
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• 제46권5호
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• pp.660-664
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• 2014

본 연구는 최근 매우 우수한 가열 매체로 인정받고 있는 저온스팀(soft steam) 열처리 공정의 natural convection (NC) 방식과 forced convection-boiler (FC-b) 및 forced convection-fan (FC-f) 방식을 이용하여 처리온도(60, 70, $80^{\circ}C$) 및 시간(0-60분)에 따른 감자의 전처리 특성을 비교 평가하고자 하였다. 스팀처리 방식에 따른 가열실 내부의 온도변화와 감자 내 외부의 온도변화, 감자의 cook value, ascorbic aicd 및 수분의 함량과 중량감소율의 변화를 관찰한 결과, 모든 처리조건에서 FC-b 및 FC-f의 강제대류 방식에 비해 자연대류의 NC 방식이 이들 전처리 특성에 대해 우수한 결과를 나타냄을 확인할 수 있었다. 따라서, 본 연구의 결과들은 감자의 가공 및 전처리를 위해 현재 사용되고 있는 기존의 열처리 공정에 대한 대안으로써 NC 방식 스팀처리의 높은 효율성 및 산업적 적용에 대한 가능성을 제시하고 있다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.1920-1925
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• 2007

A transformer is a device that changes the current and voltage by electricity induced between coil and core steel, and it is composed of metals and insulating materials. In the core of the transformer, the thermal load is generated by electric loss and the high temperature can make the break of insulating. So we must cool down the temperature of transformer by external radiators. According to cooling fan's usage, there are two cooling types, OA(Oil Natural Air Natural) and FA(Oil Natural Air Forced). For this study, we used Fluent 6.2 and analyzed the cooling characteristic of radiator. we calculated 1-fin of detail modeling that is similar to honeycomb structure and multi-fin(18-fin) calculation for OA and FA types. For the sensitivity study, we have different positions(side, under) of cooling fans for forced convection of FA type. The calculation results were compared with the measurement data which obtained from 135.45/69kV ultra transformer flowrate and temperature test. The aim of the study is to assess the Fluent code prediction on the radiator calculation and to use the data for optimizing transformer radiator design.

• 설비공학논문집
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• 제13권4호
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• pp.271-287
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• 2001

This paper has been made to investigate the thermal performance characteristics for the several types of layered aluminum heat sinks with offset-strip fin. Heat sinks with different fin height, fin length, number of fin layer and slanted fin are prepared and tested for natural convection as well as forced convection. The experimental results for layered heat sink(LHS) are compared to those for advanced pin fin heat sink (PHS) so that the appropriate heat sink can be designed or chosen according to the heating conditions. The overall heat transfer performances for LHS are almost comparable to those of PHS under natural convection, and become 1.2∼1.5 times as high as those of PHS under forced convection situation. This study shows that fin height and number of fin layer re important parameters, which have a serious influence on thermal performance for layered heat sinks.

• 한국안전학회지
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• 제14권3호
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• pp.33-39
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• 1999

In a compartment fire with openings, convective heat transfer consists of natural convection from the hot bodies and forced convection by airflow through the openings. The same finite volume method that was applied to pure natural convection in part I was utilized without modification to the square cavity with two openings. The objective of this study is to investigate effects of the openings on temperature distribution. Flow patterns, temperature distribution and heat transfer were compared for different Rayleigh numbers and with and without the openings.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.124-128
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• 2011

The heat transfer rate in an oven is very important for the quality of cooking food. For a robust performance design in an electric oven, forced convection has been used rather than natural convection, in bake and convection mode. Forced convection heat trans for in a vented electric oven has been numerically evaluated using the commercial software FLUENT. CFD modeling of the electric oven involves three-dimensional, steady state, MRF fan model and DO radiation model. In this study, the electric oven cavity and fan modules are not simplified. Other research shows that the boundary condition can often lead to non-physical solutions, such as reverse flaw at the top vent. To remove this non-physical solution, control volume has been expanded at the nearby vent. This numerical analysis has been performed with dedicated experimental support. The results show that there is less than a 2.2% difference between the simulation and experimental data for the temperature profile of food. From this research we can use this oven simulation technique to make a better convection system in an electric oven.

• 대한기계학회논문집B
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• 제31권9호
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• pp.807-813
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• 2007

Recent research on nanofluids under forced convection experiment shows that there is little relationship between convective heat transfer and thermal conductivity increase of nanofluids. This kind of new findings are totally different from the traditional theory of nanofluids, which says that the higher thermal conductivity is a prerequisite for convective heat transfer enhancement. To elucidate this controversial issue in a very comprehensible manner, simple natural convection experiment has been carried out for the water- and oil-based nanofluids. ($water-Al_2O_3$, transformer $oil-Al_2O_3$) Present research shows that there exists strong dependence between natural convection performance and thermal conductivity increase of nanofluids.

• 한국분무공학회지
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• 제1권1호
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• pp.35-43
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• 1996

A vaporization model for single component fuel droplet has been developed for applying to sub- and supercritical conditions. This model can account for transient liquid heat ins and circulation effect inside the droplet, forced and natural convection, Stefan flow effect, real gas effect and ambient gas solubility into the liquid droplet in high-pressure conditions. Thermodynamic and transport properties are calculated as functions of temperature and pressure in both phases. Numerical calculations are carried out for several validation cases with the detailed experimental data. Numerical results confirm that this supercritical vaporization model is applicable to the high-pressure conditions encountered in the combustion processes of diesel engine.