• 대한기계학회논문집B
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• 제27권7호
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• pp.963-972
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• 2003

Performance characteristics of the planar-type solid oxide fuel cell (SOFC) are investigated by the analysis of flow fields coupled with heat and mass transfer phenomena in anode and cathode channels. For these purposes, performance analysis of the SOFC is conducted based on electrochemical reaction phenomena in electrodes and electrolyte coupled with flow fields in anode and cathode channels. In the present study, the isothermal model adopted in the previous paper prepared by the same authors is extended to the non-isothermal model by solving energy equation additionally with momentum and mass transfer equations using CFD technique. It is found that the difference between isothermal and non-isothermal models come from non-uniform temperature distribution along anode and cathode electrodes by solving energy equation in non-isothermal model. Non-uniform temperature distribution in non-isothermal model contributes to the increase of average temperature of the fuel cell and influences its performance characteristics.

• 한국자동차공학회논문집
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• 제18권3호
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• pp.133-142
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• 2010

The present work focuses on the characterization of material parameters of the Overlay(multilinear hardening) model for analyzing the non-isothermal cyclic deformation. In the previous study, all the parameters were especially based on the Overlay theories, and a simple method was suggested to find out the best material parameters for the isothermal cyclic deformation analysis. Based on the previous research this paper f dther improves the isothermal parameters and suggests how to apply the isothermal parameters to the non-isothermal conditions especially for the description of TMF(Thermo-Mechanical Fatigue) hysteresis behavior. The parameters are determined and calibrated using 400 series stainless steel test data in the reference papers. For the implementation into ABAQUS, a user subroutine is developed by means of ABAQUS/UMAT. The finite element results show good agreement with test for the case of uniaxial non-isothermal cyclic loading, signifying the proposed method can be used in the TMF analysis of the converter-inserted heavy duty muffler system and the stainless steel exhaust-manifold system which are to be done in our future research.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.59-59
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• 2009

The influences of B and Si in the filler metals on microstructure and isothermal solidification during transient liquid-phase (TLP) bonding of a nitrogen-containing duplex stainless steel with MBF-30 (Ni-4.5wt.%Si-3.2wt.%B) and MBF-35 (Ni-7.3wt.%Si-2.2wt.%B), were studied at the temperature range of $1030-1090^{\circ}C$ with various times from 60 s to 3600 s under a vacuum of approximately $10^{-5}$ Torr. In case of the former, BN, $Ni_3B$ and $Ni_3Si$ precipitates were formed in the bonding region. BN and $Ni_3Si$ secondary phases were present in the joint for the latter case. The formation of $Ni_3B$ within the joint centerline is dependent on B content. The morphology of $Ni_3Si$ is dominated by Si concentration. A difference between the times for complete isothermal solidification obtained by the experiments and the conventional TLP bonding diffusion model was observed when using MBF-35. According to the simulated results, the isothermal solidification completion time for MBF-35 case was smaller than that in MBF-30. However, this experimental value obtained using MBF-35 was notably larger than that obtained using MBF-30. Isothermal solidification of liquid MBF-30 is controlled by the first isothermal solidification regime dependent on B diffusion model, whereas that of liquid MBF-35 experiences two isothermal solidification regimes and is mainly controlled by the second isothermal solidification dependent on Si diffusion model. In addition, only if Si content exceeds a critical value, the slower 2nd solidification regime will commence.

• 한국화재소방학회논문지
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• 제23권6호
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• pp.111-115
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• 2009

아세톤 LIF와 Rayleigh 산란법 등 두 가지 레이저 측정 기법을 이용하여 Re수가 1,000 미만의 부력제트 노즐근처에서의 공기 유입을 실험적으로 조사하였다. 아세톤 LIF 실험결과 전체적인 혼합기구는 경계면에서의 불안정성에 의한 거대와구조로 판단되고, Re 수가 커질수록 유입되는 시점이 상류로 이동하며 그 양 또한 증가되었다. 또한 Rayleigh 산란법 결과는 상류에서도 혼합이 제트의 내부까지 이루어지고, 노즐에서 분사방향으로 진행할수록 주위공기의 유입이 제트 내부로 진행되고 있음을 알 수 있다. 이 실험결과로서 기존 등온기체모델에서 제트의 주위공기 유입을 고려하여야 한다는 사실을 입증할 수 있다. 또한, 이상적 플룸식에서 복사열손실을 0.35로 고려하였을 경우에 기존의 연기량 및 온도 예측과 근사한 결과를 얻을 수 있으며, 주위공기 유입효과를 고려하여 보다 간단하면서 정확한 등온기체 모델링 방법을 얻을 수 있다.

• Computers and Concrete
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• 제9권3호
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• pp.179-193
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• 2012

The hydration of cement contributes to the performance characteristics of concrete, such as strength and durability. In order to improve the utilization efficiency of cement and its early properties, the particle size distribution (PSD) of cement varies considerably, and the effects of the particle size distribution of cement on the hydration process should be considered. In order to evaluate effects of PSD separately, experiments testing the isothermal heat generated during the hydration of cements with different particle size distributions but the same chemical composition have been carried out. The measurable hydration depth for cement hydration was proposed and deduced based on the experimental results, and a PSD hydration model was developed in this paper for simulating the effects of particle size distribution on the hydration process of cement. First, a reference hydration rate was derived from the isothermal heat generated by the hydration of ordinary Portland cement. Then, the model was extended to take into account the effect of water-to-cement ratio, hereinafter which was referred to as PSD hydration model. Finally, the PSD hydration model was applied to simulate experiments measuring the isothermal heat generated by the hydration of cement with different particle size distributions at different water-to-cement ratios. This showed that the PSD hydration model had simulated the effects of particle size distribution and water-to-cement ratio on the hydration process of cement with satisfactory accuracy.

• 동력기계공학회지
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• 제14권5호
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• pp.71-75
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• 2010

Leak detection technology is a challenging research until nowadays, because it has wide and various applications in industry. Furthermore pneumatic component reliability test based on ISO requires air leakage measurement. The conventional measurement methods need a complex operation and the calibration of leak detector. Tracing the history of our study, we proposed a new method for measurement of leak flow rate using isothermal chamber. In this study, propose a simulation model of isothermal chamber by infinitesimal flow -rate, such as a leak flow-rate. The effectiveness of the proposed simulation model is proved by simulation and experimental results. Base on the comparison results, proposed simulation model is good agreement with experimental results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.783-788
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• 2001

Choosing the most suitable mathematical model and relating this to turbulent tangential tensions model are very important in the investigations of turbulent two-phase flow. This paper considers two-fluid scheme. According to it, two phases have their own densities, velocities, and temperatures at any spatial point and at any moment. The equations of motion and heat transfer for each phase are linked with the forces of interaction between two phases. These forces are considered as predominant for the flow. As a closure in the system of motion equations, one modification of $K - {\epsilon}$ turbulent model is worked out. The modification uses two equations for turbulent kinetic energy of the phases and one - for the turbulent energy loss of main phase. This model can be set as a $K_g - K_p -{\epsilon}$ model. The modified model has been tested for both a two-phase non-isothermal flat jet and axially symmetrical jet. The numerical results are compared with the reference data revealing a good agreement between them.

• 폴리머
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• 제24권1호
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• pp.105-112
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• 2000

본 연구에서는 항공기 구조용 재료로 쓰이는 탄소섬유/에폭시 복합재료 프리프레그(DMS 2224)를 모델시스템으로 하여 등온환경과 등속도 가열환경에서 경화반응 속도를 연구하였다. 이 복합재료의 공정온도에서의 가공공정을 묘사할 수 있는 현상학적인 반응속도 모델을 differential scanning calorimetry (DSC)와 이론을 통하여 제안하였다. 등온환경에서의 실험으로부터 반응특성곡선을 관찰한 결과 경화반응이 1차 반응함수임을 확인하였고, 활성화 에너지는 78.43 kJ/mo1을 얻었다. 이 프리프레그는 경화온도에 따라 한계경화도를 보여주어 유리화가 존재함을 확인하였고 이를 1차 반응속도 모델에 적용시킨 결과, 유리화 이후의 확산우세현상을 포함한 반응속도 모델을 제안하였다. 제안된 모델식을 이용하여 등온/등속도 가열환경을 포함한 실제 경화공정을 성공적으로 표현할 수 있었다.

• 한국자동차공학회논문집
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• 제4권5호
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• pp.130-141
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• 1996

Numerical study of a confined, swirling, isothermal and spray-combusting flows has been presented. The pressure-velocity coupling in the Eulerian gas-phase equation is handled by the improved PISO algorithm. The droplet dispersion by turbulence is introduced by a Stochastic Separated Flow(SSF) model. The k-$\varepsilon$ turbulence model and the eddy dissipation model are employed to account for turbulence-combustion interaction. The detailed comparison with experimental data has been made for the isothermal jet swirling flows and the nearly monodisperse spray-combusting flow in the swirl combustor.

• 대한기계학회논문집A
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• 제30권7호
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• pp.757-764
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• 2006

Isothermal cyclic stress-strain deformation and thermomechanical deformation (TMD) of 429EM stainless steel were analyzed using a rheological model employing a bi-linear model. The proposed model was composed of three parameters: elastic modulus, yield stress and tangent modulus. Monotonic stress-strain curves at various temperatures were used to construct the model. The yield stress in the model was nearly same as 0.2% offset yield stress. Hardening relation factor, m, was proposed to relate cyclic hardening to kinematic hardening. Isothermal cyclic stress-strain deformation could be described well by the proposed model. The model was extended to describe TMD. The results revealed that the hi-linear thermomechanical model overestimates the experimental data under both in-phase and out-of-phase conditions in the temperature range of $350-500^{\circ}C$ and it was due to the enhanced dynamic recovery effect.