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RISS 인기검색어
- 검색키워드
- 저자 : M. Kaviany (검색결과 7 건)
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Thermophotovoltaic power conversion using a superadiabatic radiant burner
Wu, H.,Kaviany, M.,Kwon, O.C. Elsevier 2018 APPLIED ENERGY Vol.209 No.-
<P>A new configuration of a 5-10 W thermophotovoltaic (TPV) device integrated with a porous superadiabatic radiant burner (SRB) is suggested and experimentally studied. The silicon carbide (SiC) SRB (emitter) consists of a small-pored upstream section (PM1) and a large-pored downstream section (PM2). PM1 is the section where the incoming fuel-air mixture is preheated internally and PM2 is the section where flame is established. Also, a separate preheater is attached on the SRB to externally recover heat from the exiting flue gas and preheat the inlet air for the burner, and radiation rods are embedded at the interface between the PM1 and PM2 to extract heat from the flame and transfer it to radiating disk surfaces. Radiation from the disk surface is used for the TPV power conversion, reaching gallium antimonide photovoltaic cells (PVCs) with proper quantum efficiencies (up to 80%) through a quartz plate for preventing direct convectional heat transfer from the exhaust gas onto the PVCs. Under optimized conditions, uniform radiation provides adequate TPV performance, particularly indicating reasonable emitter efficiencies (up to 32%) with the enhanced disk temperature even for fuel-lean condition. Thus, the present configuration of the SRB-integrated TPV device can be used in practical applications, avoiding high-level noise without any moving parts.</P>
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Kim, W.K.,Shim, J.H.,Kaviany, M. North Holland Pub. Co 2017 Journal of nuclear materials Vol.491 No.-
<P>Predicting the fate of accident-melted nuclear fuel-cladding requires the understanding of the thermophysical properties which are lacking or have large scatter due to high-temperature experimental challenges. Using equilibrium classical molecular dynamics (MD), we predict the properties of melted UO2 and ZrO2 and compare them with the available experimental data and the predictive models. The existing interatomic potential models have been developed mainly for the polymorphic solid phases of these oxides, so they cannot be used to predict all the properties accurately. We compare and decipher the distinctions of those MD predictions using the specific property-related autocorrelation decays. The predicted properties are density, specific heat, heat of fusion, compressibility, viscosity, surface tension, and the molecular and electronic thermal conductivities. After the comparisons, we provide readily usable temperature-dependent correlations (including UO2-ZrO2 compounds, i.e. corium melt). (C) 2017 Elsevier B.V. All rights reserved.</P>
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Ahn, H.S.,Kim, J.M.,Kaviany, M.,Kim, M.H. Pergamon Press ; Elsevier Science Ltd 2014 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.78 No.-
The critical heat flux (CHF) during reduced graphene oxide (RGO) colloid pool boiling was increased by the development of coating layers from the RGO flakes. By boiling water after boiling RGO colloid, we confirmed that the CHF enhancement was due to the development of RGO coating layers such as the base graphene layer (BGL), self-assembled foam-like graphene structure (SFG), and thickly aggregated graphene layer (TGL). During RGO colloid boiling, we observed an interesting phenomenon after the CHF point: when the heat flux reached the maximum value (CHF), the wall temperature slowly began to increase while the heat flux was maintained, unlike the rapid wall temperature increase that is observed during water boiling. We examined the stability of this phenomenon and the boiling hysteresis in relation to the heat flux. We hypothesized that the BGL and SFG could induce this phenomenon by functioning as heat spreaders, owing to the greatly enhanced thermal conductivity during the formation of hot/dry spots, and the vapor escape resistance during boiling on a porous medium.
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Breakthrough/drainage pressures and X-ray water visualization in gas diffusion layer of PEMFC
Kim, J.,Je, J.,Kim, T.,Kaviany, M.,Son, S.Y.,Kim, M. Elsevier 2012 Current Applied Physics Vol.12 No.1
The primary role of the gas diffusion layers (GDLs) in polymer electrolyte membrane fuel cells (PEMFC) is to maintain the delicate balance between water retention and removal in GDLs. Water management in the fuel cell is related to the breakthrough pressure at which water starts to pass through GDL, and the drainage pressure, which is maintained after the breakthrough. These pressures are both related to water management in fuel cells. Here we measured these pressures for two different GDLs and used X-ray tomography to visualize the water distributions within them. We then relate the variations in liquid pressures to the visualization and discuss water management in PEMFC.
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Experiment on superadiabatic radiant burner with augmented preheating
Wu, H.,Kim, Y.J.,Vandadi, V.,Park, C.,Kaviany, M.,Kwon, O.C. Elsevier 2015 APPLIED ENERGY Vol.156 No.-
<P><B>Abstract</B></P> <P>A radiant porous burner with augmented preheating (i.e., superadiabatic radiant burner, SRB) is experimentally investigated. The porous alumina (Al<SUB>2</SUB>O<SUB>3</SUB>) burner with a square cross-section consists of a small-pored upstream section for internally preheating the incoming gas mixture, a large-pored downstream section for establishing flame, a preheater for externally recovering heat from the exiting flue gas and preheating the inlet air for the burner in addition to the internal heat recirculation in the small-pored upstream section, and radiation corridors for extracting heat from the flame and transferring it to radiating disk surfaces. Temperature distribution and combustion stability limits of flame in the SRB and the nitrogen oxide (NO<SUB>x</SUB>) and carbon monoxide (CO) emissions are measured. Results show that the SRB can be operated even at very fuel-lean condition because of the internal and external heat recirculation, showing blow-off and flash-back limits for a given fuel-equivalence ratio. It is observed that the superadiabatic radiation temperature on the disk surfaces is higher than the flue gas temperature at the same axial location, experimentally confirming the previous theoretical and computational results of SRBs. Improved performance of CO and NO<SUB>x</SUB> emissions compared with the conventional porous radiant burners also indicates that the SRB is acceptable for practical application.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Potential of superadiabatic radiant burners (SRBs) is experimentally confirmed. </LI> <LI> The SRB consists of two-layered porous media, a preheater and radiation rods. </LI> <LI> The SRB can be operated at very fuel-lean condition due to enhanced heat recovery. </LI> <LI> CO/NO<SUB>x</SUB> emissions are reduced compared with the conventional porous radiant burners. </LI> <LI> The SRB is acceptable for practical applications. </LI> </UL> </P>
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