Yuseong gu, South Korea
Yuseong gu, South Korea

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Park H.,Korea Research Institute of Chemical Technology | Kim J.,Gwangju Institute of Science and Technology | Jung H.,Korea Radioactive Waste Agency | Seo J.,Korea Research Institute of Chemical Technology | Choi H.,Gwangju Institute of Science and Technology
Water, Air, and Soil Pollution | Year: 2014

A granular media synthesized using iron oxide nanoparticle-coated alumina (IONA) has been demonstrated as an effective solid catalyst in the heterogeneous catalytic ozonation of para-chlorobenzoic acid (pCBA). TEM analysis showed that iron oxide nanoparticles with an average size of 5-20 nm were well-coated onto an alumina surface. It was determined that the iron oxide nanoparticle coating increased the specific surface area by 54 times and the functional group density by 1.5 times. During catalytic ozonation at acidic pH levels, it was clearly observed that IONA increased the degradation of pCBA (98%) through effective hydroxyl radical formation compared to bare alumina (9%) under continuous ozonation processes. In comparing the Rct value, which represents the ratio of ozone exposure to hydroxyl radical exposure, the Rct of IONA was approximately four times higher than for bare alumina. In addition, IONA showed good stability for catalytic ozonation of pCBA in the reusability tests. © Springer International Publishing 2014.

Kang G.-U.,Korea Radioactive Waste Agency | Chung B.-J.,Kyung Hee University
International Journal of Heat and Mass Transfer | Year: 2015

Natural convection heat transfer was investigated in vertical cavities where either all surfaces were active, or only the vertical surface was active for four different geometries, which were varied by placing a disk at the top and/or bottom of the cavity. A cupric acid-copper sulfate electroplating system was employed for mass transfer experiments exploiting the analogy with heat transfer. The Rayleigh number was varied in the range 4.55 × 109 ≤ RaLw ≤ 3.79 × 1013. Preliminary tests for a vertical pipe, upward- and downward-facing horizontal disks showed good agreement with existing correlations. The measured Nusselt numbers in the vertical cavities with all surfaces active were always greater than those with only the vertical surface active, which is attributed to greater hydrodynamic interaction of the flows generated by different surfaces. When all surfaces were active, the bottom-closed cavity exhibited the largest heat transfer rates, followed by both-closed, top-closed, and both ends open cavities; this trend was observed with laminar and turbulent flows. With only the vertical surface active, similar trends were observed except that the heat transfer rates were almost identical for both-open and top-closed cavities, which is attributed to the weak influence of the top disk on the heat transfer characteristics. Using these results, empirical correlations were derived for both laminar and turbulent flow conditions. © 2015 Elsevier Ltd. All rights reserved.

Kang G.-U.,Korea Radioactive Waste Agency | Chung B.-J.,Kyung Hee University | Kim H.-J.,Korea Radioactive Waste Agency
International Journal of Heat and Mass Transfer | Year: 2014

Natural convection experiments on both vertical thin- and thick-cylinders were performed for Rayleigh numbers from 1.4 × 109 to 3.2 × 1013, the H/DO from 0.6 to 140 at high Prandtl numbers. A sulfuric acid-copper sulfate electroplating system based on analogy concepts were employed for the measurements of heat transfer rates. For vertical thin-cylinders, Nusselt numbers were in satisfactory agreements with the existing correlation on vertical plates. Especially, those measured at the high H/DO were higher even though the thermal boundary layer is much thinner than the cylinder diameter. This was due to the flow interactions, which promoted the development of momentum boundary layer and velocity fluctuations, leading to the enhancement of the Nusselt number. For vertical thick-cylinders, Nusselt numbers in laminar flows were in satisfactory with the existing correlations. However, those in turbulent flows decreased as Prandtl number increased in this study. Its phenomena are caused by the formation of very thin thermal boundary layer within viscous sublayer by very high Prandtl number. In this case, the velocity within thermal boundary layer becomes very low by no-slip condition near the heated wall and the heat is transferred by conduction rather than advection. Based upon the results, empirical correlations on vertical thick-cylinders were derived for laminar and turbulent flows. © 2014 Elsevier Ltd. All rights reserved.

Kim H.,Korea Radioactive Waste Agency | Kwon O.J.,Korea Advanced Institute of Science and Technology | Kang G.-U.,Korea Radioactive Waste Agency | Lee D.-G.,Hyundai Engineering
Annals of Nuclear Energy | Year: 2014

When spent fuel assemblies from the reactor of nuclear power plants (NPPs) are transported or stored, the assemblies are exposed to a variety of environments that can affect the peak cladding temperature. There are three models to calculate the peak cladding temperature of spent fuel assemblies in a cask: Manteufel and Todreas's two-region model, Bahney Lotz's effective thermal conductivity model, and Wooton-Epstein correlation. The peak cladding temperatures of Babcock & Wilcox (B&W) 15 × 15 PWR spent fuel assembly under helium backfill gas were evaluated by using two-dimensional CFD simulation and compared with two models (Wooton-Epstein correlation, two-region model). The peak cladding temperature difference between the two-region model and CFD simulation ranges from -0.2 K to 9 K. Two-region model over-predicts the measured peak cladding temperature that performs in a spent fuel dry storage cask. Therefore the simulation could be used to calculate peak cladding temperature of spent fuel assemblies. Application using CFD simulation was conducted to investigate the peak cladding temperature and effective thermal conductivity of spent fuel assembly used in Korea NPPs: 16 × 16 (CE type) and 17 × 17 (WH type) PWR spent fuel assembly. CFD simulation results are similar to each other, and the difference of temperature drop between the three arrays occurs slightly in all basket wall temperatures. The effective thermal conductivity calculated from the 16 × 16 PWR spent fuel assembly results was more conservative than those for the 17 × 17 array. © 2014 Elsevier Ltd. All rights reserved.

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