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FARO tests corium-melt cooling in water pool: Roles of melt superheat and sintering in sediment
Hwang, Gisuk,Kaviany, Massoud,Moriyama, Kiyofumi,Park, Hyun Sun,Hwang, Byoungcheol,Lee, Mooneon,Kim, Eunho,Park, Jin Ho,Nasersharifi, Yahya Elsevier 2016 Nuclear engineering and design Vol.305 No.-
<P><B>Abstract</B></P> <P>The FARO tests have aimed at understanding an important severe accident mitigation action in a light water reactor when the accident progresses from the reactor pressure vessel boundary. These tests have aimed to measure the coolability of a molten core material (corium) gravity dispersed as jet into a water pool, quantifying the loose particle diameter distribution and fraction converted to cake under range of initial melt superheat and pool temperature and depth. Under complete hydrodynamic breakup of corium and consequent sedimentation in the pool, the initially superheated corium can result in debris bed consisting of discrete solid particles (loose debris) and/or a solid cake at the bottom of the pool. The success of the debris bed coolability requires cooling of the cake, and this is controlled by the large internal resistance. We postulate that the corium cake forms when there is a remelting part in the sediment. We show that even though a solid shell forms around the melt particles transiting in the water pool due to film-boiling heat transfer, the superheated melt allows remelting of the large particles in the sediment (depending on the water temperature and the transit time) using the COOLAP (Coolability Analysis with Parametric fuel-cooant interaction models) code. With this remelting and its liquid-phase sintering of the non-remelted particles, we predict the fraction of the melt particles converting to a cake through liquid sintering. Our predictions are in good agreement with the existing results of the FARO experiments. We address only those experiments with pool depths sufficient/exceeding the length required for complete breakup of the molten jet. Our analysis of the fate of molten corium aimed at devising the effective scenarios for its safe cooling in the containment so that predicted the minimum pool depth for no cake formation as functions of the melt superheat and water (subcooled/saturation) temperatures.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The numerical approach for FARO experimental data is suggested. </LI> <LI> The cooling mechanism of ex-vessel corium is suggested. </LI> <LI> The predicted minimum pool depth for no cake formation is suggested. </LI> </UL> </P>
Quasi-steady front in quench subcooled-jet impingement boiling: Experiment and analysis
Lee, Sang Gun,Kaviany, Massoud,Kim, Charn-Jung,Lee, Jungho Elsevier 2017 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.113 No.-
<P><B>Abstract</B></P> <P>Boiling heat transfer of subcooled water jet impingement on highly superheated plate is investigated with heat transfer analysis and high-definition flow visualization. The stainless steel plate initially heated up to 900°C by an induction heating is quenched with the water temperature of 15°C. The surface temperature and heat flux are estimated by solving 2-D inverse heat conduction problem. The temporal visualization during quench subcooled-jet impingement boiling is synchronized with the heat transfer measurement in the corresponding surface temperature and heat flux. Spread of the subcooled jet over the horizontal plate shows a quasi-steady regime where the wetting front spreads linearly with time. The time for onset of the quasi-steady regime can be explained by a quasi-steady time. The front separates the single-phase/collapsed-bubble region from the outside region which is dry if not for the impinging droplets ejected from the front. As the front expands, the surface experiences a sequence of single-phase, collapsed-bubble, wetting front evaporation and ejected-droplet evaporation cooling. The fraction of water ejected from the front increases linearly with time (reaches over 10%) and is also predicted.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Very high initial temperature (900°C) and large surface area features of quench jet impingement boiling was characterized with simultaneous measurement between high-resolution flow visualization and inverse heat conduction. </LI> <LI> Quench jet impingement exhibits 4 significant regimes: (i) single-phase, (ii) collapsed-bubble (subcooled boiling), (iii) wetting front with ejecting droplets, and (iv) evaporating-droplets cooling regions on the plate. </LI> </UL> </P>
Breakthrough/drainage pressures and X-ray water visualization in gas diffusion layer of PEMFC
김종록,제준호,김태주,Massoud Kaviany,손상영,김무환 한국물리학회 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.
Quench subcooled-jet impingement boiling: Two interacting-jet enhancement
Lee, Sang Gun,Kaviany, Massoud,Lee, Jungho Elsevier 2018 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.126 No.1
<P><B>Abstract</B></P> <P>Enhancement resulting from interaction of two adjacent jets impinging on largely superheated stainless-steel plate (900 °C, initial induction heating) is recorded and analyzed with inverse-conduction analysis and high-definition visualization. Subcooled water jets (20 °C, 1 atm, Reynolds number 1.5 × 10<SUP>4</SUP>) with varying jet separation distance <I>W</I> (up to 30 nozzle diameters of <I>D<SUB>n</SUB> </I>) show that the spreading liquid wetting fronts merge and the heat transfer coefficient increases substantially in the merged region, which follows an elapsed time of isolated-jet behavior. This enhancement is presented as the time-dependent two-jet cooling effectiveness with a peak of 1.6 (60% enhancement) for <I>W/D<SUB>n</SUB> </I> = 10 at <I>t</I> = 3 s, followed by decay. This enhancement decreases with increasing <I>D<SUB>n</SUB> </I>, but overlapping jets create some enhancement for all jet separations. In the interaction region, the plate undergoes rapid temperature drop (by lateral conduction toward the jet centers), reaching large cooling rate of 600 K/s.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effect of two interacting impinging jets on the boiling heat transfer characteristics is simultaneously measured and analyzed with high-resolution boiling visualization on extreme superheated stainless steel plate (900 °C). </LI> <LI> The enhancement is presented as the cooling effectiveness of two interacting jets compared with that of a previous single jet study , and which initially increases with the jet-to-jet distance of <I>W</I>, reaching a peak of 60% at <I>W/D<SUB>n</SUB> </I> = 10 and then decreases for larger <I>W</I>. </LI> </UL> </P>
Tunable, self-assembled 3D reduced graphene oxide structures fabricated via boiling
Jo, HangJin,Noh, Hyunwoo,Kaviany, Massoud,Kim, Ji Min,Kim, Moo Hwan,Ahn, Ho Seon Elsevier 2015 Carbon Vol.81 No.-
<P><B>Abstract</B></P> <P>To exploit the favorable mechanical and electrical properties of graphene in practical applications, control over the dimensionality and geometry of assembled graphene structures is required. Here, we report the use of boiling with reduced graphene oxide (RGO) colloidal dispersion to form self-assembled three-dimensional (3D) RGO structures. The morphology of the resulting self-assembled RGO structures could be controlled by varying the heat flux during boiling. A large heat flux resulted in continuous bubble nucleation at the surface, and consequently, the interference exhibited aggregates of RGO flakes around the bubble nucleation site due to repetitive expansion and contraction of the bubble triple line. As the water evaporated, self-assembled foam-like graphene (SFG) was formed. As the heat flux increased, more vigorous agitation occurred at the interface, which led to smaller pores in the structures. With a low heat flux, the less vigorous bubble interference dynamics led to interactions between the RGO flakes, and consequently, self-assembled bump-like graphene (SBG) structures were formed, which were not porous. The self-assembled RGO 3D structures exhibited favorable mechanical and electrical properties compared with conventional 3D self-assembled graphene- or carbon-based structures. Such controllable 3D RGO structures with good mechanical and electrical properties have potential applications.</P>