• Journal of Welding and Joining
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• v.15 no.5
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• pp.134-143
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• 1997

The formation of thick alloyed layer with high Si content have been investigated on the surface of Al alloy (A5083) plate by PTA process with Si powder. Hardening characteristics and wear resistance of alloyed layer was examined in relation to the microstructure of alloyed layer. Thick hardened layer in mm-order thickness on the surface of A5083 plate can be formed by PTA process with wide range of process condition by using Si powder as alloying element because of eutectic reaction of Al-Si binary alloy. High temperature and rapid solidification rate of molten pool, which are features of PTA process, enable the formation of high Si content alloyed layer with uniform distribution of fine primary Si paticle. High plasma arc current was beneficial to make the alloyed layer with smooth surface appearance in wide range of powder feeding rate, because enough volume of molten pool was necessary make alloyed layer. Uniform dispersion of fine primary Si particle with about 30${\mu}{\textrm}{m}$ in particle size can be obtained in layer with Si content ranging from 30 to 50 mass %. Hardness of alloyed layer increased with increasing Si content, but increasing rate of hardness differed with macrostructure of alloyed layer. Wear resistance of alloyed layer depended on $V_{si}$(volume fraction of primary Si) and was remarkably improved to two times of base metal at 20-30% $V_{si}$ without cracking, but no more improvement was obtained at larger $V_{si}$.

• Journal of the Korean Electrochemical Society
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• v.8 no.4
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• pp.155-161
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• 2005

In this paper, commercial CFD program FLUENT v5.3 is used for simulation of MCFC stack. Besides using conservation equations included in FLUENT by default, mass change, mole fraction change and heat added or removed due to electrochemical reactions and water gas shift reaction are considered by adding several equations using user defined function. The stacks calculated are 6 and 25 kW class coflow stack which are composed of 20 and 40 unit cells respectively. Simulation results showed that pressure drop took place in the direction of gas flow, and the pressure drop of cathode side is more larger than that of anode side. And the velocity of cathode gas decreased along with the gas flow direction, but the velocity of anode gas increased because of the mass and volume changes by the chemical reactions in each electrodes. Simulated temperature profile of the stack tended to increase along with the gas flow direction and it showed similar results with the experimental data. Water gas shift reaction was endothermic at the gas inlet side but it was exothermic at the outlet side of electrode respectively. Therefore water gas shift reaction played a role in increasing temperature difference between inlet and outlet side of stack. This results suggests that the simulation of large scale commercial stacks need to consider water gas shift reaction.

• Nuclear Engineering and Technology
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• v.32 no.4
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• pp.395-409
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• 2000

Parametric studies were performed to assess the sensitivity in determining the maximum in-vessel heat removal capability from the core material relocated into the lower plenum of the reactor pressure vessel (RPV）during a core melt accident. A fraction of the sensible heat can be removed during the molten jet delivery from the core to the lower plenum, while the remaining sensible heat and the decay heat can be transported by rather complex mechanisms of the counter-current flow limitation (CCFL) and the critical heat flux (CHF）through the irregular, hemispherical gap that may be formed between the freezing oxidic debris and the overheated metallic RPV wall. It is shown that under the pressurized condition of 10MPa with the sensible heat loss being 50% for the reactors considered in this study, i.e. TMI-2, KORI-2 like, YGN-3&4 like and KNGR like reactors, the heat removal through the gap cooling mechanism was capable of ensuring the RPV integrity as much as 30% to 40% of the total core mass was relocated to the lower plenum. The sensitivity analysis indicated that the cooling rate of debris coupled with the sensible heat loss was a significant factor The newly proposed heat removal capability map (HRCM) clearly displays the critical factors in estimating the maximum heat removal from the debris in the lower plenum. This map can be used as a first-principle engineering tool to assess the RPV thermal integrity during a core melt accident. The predictive model also provided ith a reasonable explanation for the non-failure of the test vessel in the LAVA experiments performed at the Korea Atomic Energy Research Institute (KAERI), which apparently indicated a cooling effect of water ingression through the debris-to-vessel gap and the intra-debris pores and crevices.