• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1997년도 추계 학술대회논문집
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• pp.23-28
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• 1997

A parallel implementation is made of a two-dimensional finite volume model based on the SIMPLER. The solution domain is decomposed into several subdomains and the solution at each subdomain is acquired by parallel use of multiple processors. Communications between processors are accomplished by using the standard MPI and the Cray-specific SHMEM. The parallelization method for the overall solution procedure to the Navier-Stokes equations is described in detail, The parallel implementation is validated on the Cray T3E system for a benchmark problem of natural convection in a sidewall-heated cavity. The parallel performance is assessed and the issues encountered in achieving a high-performance parallel model are elaborated.

• 한국막학회:학술대회논문집
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• 한국막학회 1995년도 춘계 총회 및 학술발표회
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• pp.6-10
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• 1995

An inevitable problem feature of membrane processing is concentration polarization (CF) which is a result of the accumulation of retained solutes at the membrane surface. In ultrafiltration (UF), this accumulation can lead to fouling due to the irreversible deposition of macromolecules both at the membrane surface and in the membrane pores. To reduce or control CP and folding, many possible methods have been considered [1]. One of the most effective approaches is to induce fluid instability near the membrane surface by using pusation flow [2, 3], Taylor [4] and Dean [5, 6] vortex flows. Winzeler and Belfort [6] have comprehensively reviewed several possible attempts to use fluid instabihties for improved membrane performance.

• International Journal of Air-Conditioning and Refrigeration
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• 제8권2호
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• pp.11-22
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• 2000

Holographic interferometric tomography can provide reconstruction of instantaneous three-dimensional gross flow fields. The technique however confronts ill-posed reconstruction problems in practical applications. Experimental data are usually limited in projection and angular scanning when a field is captured instantaneously or under the obstruction of test models and test section enclosures. An algorithm, based on a series expansion method, has been developed to improve the reconstruction under the ill-posed conditions. A three-dimensional natural convection flow around two interacting isothermal cubes is experimentally investigated. The flow can provide a challenging reconstruction problem and lend itself to accurate numerical solution for comparison. The refractive index fields at two horizontal sections of the thermal plume with and without an opaque object are reconstructed at a limited view angle of 80$\circ$. The experimental reconstructions are then compared with those from numerical calculation and thermocouple thermometry. It confirms that the technique is applicable to reconstruction of reasonably complex, three-dimensional flow fields.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2524-2529
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• 2008

The thermal system like a combustion chamber is believed to experience a significant instability problem with vibration in case that the thermal energy or the acoustic energy are transformed into a different form through a relevant path. This study deals with a numerically- predicted, Thermoacoustic instability in a Rijke tube by using a non-linear model for a heat source. The heating part where the energy transformation occurs actively is modeled after simulating two-dimensional cylinder case with constant surface temperature, and a nonlinear model that accounts for the transfer function of magnitude- and phase-characteristics is properly implemented so as to be dependent on the pulsation strength in the tube. The heat source model is observed to result in equivalent Thermoacoustic instabilities in the Rijke tube except low flow-rate cases in which the natural convection is dominant.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 B
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• pp.993-995
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• 2005

Recently, the efficiency of power transformer is improved as well as the size is becoming smaller. So, it is very important that temperature characteristics of the transformer should be estimated and predicted precisely. This paper deals with the temperature distribution of power transformer by simplified 2-D hybrid mesh model. The temperature distribution of model transformer was obtained by CFD algorithm considering natural convection. Heat sources are calculated first by magnetic field analysis based on F.E.M. and are usedas the input data for thermal field problem based on computational fluid dynamics(CFD) algorithm. The calculated temperature distribution of the simplified 2-D power transformer model shows good results in accuracy as well as in computing time.

• 대한설비공학회지:설비저널
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• 제14권3호
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• pp.200-211
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• 1985

The paper discusses the problem of the reduction in Coefficient of Performance (COP) in a refrigerator due to the inadequate position or some flow obstacles such as shelves in a room. The propriety of the present numerical method has teen proved by experiments using the flow visualization technique. The COP are calculated from the temperature rise of the condenser whose temperature indicates the condensing temperature of refrigerant The temperature rise is predicted by the theory of the steady two-dimensional laminar natural convection. In a room size of $2m\;{\times}\;2m$ the COP are decreased by 0.3 when the gap between the wall and condenser are decreased from 10cm to 2cm. While the COP are decreased by 0.55 as the shelf length increases from 0 to 75cm.

• 한국산학기술학회논문지
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• 제10권5호
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• pp.955-961
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• 2009

현재 소형 휴대용 배터리의 용량 증가에 따라 배터리 부피가 커지는 문제를 가지고 있다. 이러한 문제를 해결하기 위해 직접 메탄올 연료전지가 대안으로 떠오르고 있다. 본 논문에서는 직접 메탄올 연료전지를 상온 상태에서 자연 대류 방식으로 공기를 공급하고, 메탄올의 농도와 유량의 변화에 대한 특성을 분석하였다. 분석 결과 저 농도의 메탄올에서는 수소 이온의 확산 속도 지연에 따른 분극현상이 발생하였고, 메탄올의 공급량이 높을수록 전지 Cell의 냉각 효과가 발생하여 출력이 감소한다.

• 한국태양에너지학회 논문집
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• 제33권6호
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• pp.85-91
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• 2013

It is essential to reduce the amount of fossil fuel because facing with the natural problem such as a global warming. To achieve this goal, many of interests in the use of renewable energy is growing. Especially, as one of these renewable energy systems, a solar air heater invention has been conducted for enhancing the efficiency of solar air heater. According to this trend, scale-down sized experiment apparatus was constructed and performed for searching a proper fin and confirming the heat transfer performance by fin shape on constant heat condition to enhance efficiency of solar air heater. In this experiment, heat gain, convection heat transfer coefficient, number of transfer units, Nusselt number, Reynold's number, friction factor, performance factor were investigated in order to evaluate the thermal characteristics based on the real data obtained. By comparison with the each fin performance, a zigzag shape keeping a right angle to the plate had the highest value among them.

• 대한기계학회논문집B
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• 제22권12호
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• pp.1657-1668
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• 1998

In the analysis of a mushy solidification system with natural convection using a fixed grid method, the enthalpy method has been used to account for the release of latent heat. The variable viscosity, Darcy source, and hybrid methods have been employed for the velocity suppression in a mushy region. The choice of the values of solid viscosity and permeability constant in conjunction with the Darcy source term plays an important role in forming the location and shape of the phase boundaries. In this work the effects of these major parameters related to steady-state behavior in the system of mushy solidification are investigated through a simple test problem. The effective specific heat based on the spatial gradients of the enthalpy and temperature is adopted for the treatment of the release of latent heat. The effects of the Prandtl and Rayleigh numbers on the shape of mushy region are examined using the hybrid method.

• Nuclear Engineering and Technology
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• 제41권7호
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• pp.929-944
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• 2009

The present study is concerned with the extension of the Effective Convectivity Model (ECM) to the phase-change problem to simulate the dynamics of the melt pool formation in a Light Water Reactor (LWR) lower plenum during hypothetical severe accident progression. The ECM uses heat transfer characteristic velocities to describe turbulent natural convection of a melt pool. The simple approach of the ECM method allows implementing different models of the characteristic velocity in a mushy zone for non-eutectic mixtures. The Phase-change ECM (PECM) was examined using three models of the characteristic velocities in a mushy zone and its performance was compared. The PECM was validated using a dual-tier approach, namely validations against existing experimental data (the SIMECO experiment) and validations against results obtained from Computational Fluid Dynamics (CFD) simulations. The results predicted by the PECM implementing the linear dependency of mushy-zone characteristic velocity on fluid fraction are well agreed with the experimental correlation and CFD simulation results. The PECM was applied to simulation of melt pool formation heat transfer in a Pressurized Water Reactor (PWR) and Boiling Water Reactor (BWR) lower plenum. The study suggests that the PECM is an adequate and effective tool to compute the dynamics of core melt pool formation.