Governing equations for heat and mass transfer in heat-generating porous beds—I. Coolant boiling and transient void propagation

It has been proposed as a reactor design option to line the bottom of the guard vessel with magnesia (MgO) bricks to retain the core debris following a core-disruptive accident. With conduction as the dominant mode of heat transfer in the debris bed and natural convection in the overlying pool, the debris bed, while fully submerged in sodium coolant, may begin to heat up and lead to coolant boiling. During boiling, to determine transient void distribution, a void propagation equation is derived. The transient aspects of the void distribution are expected to be important for very deep beds and during debris bed quenching. The vapor production source term is obtained from the solution of energy equation for the two-phase coolant, whereas the temperature distribution in the solid phase is calculated from the conduction equation. The heat flux from the fuel particulate to the two-phase coolant is modeled from the solution of steady-state two-phase continuity, momentum and energy equations.     

Green's function solution of temperature field for flow in porous passages

Recently, the heat transfer in porous passages has received attention from many investigators. The Green's function solution method can serve as a powerful tool to accomplish this task of providing solutions to this type of problems with or without the effect of axial conduction. The study of heat transfer with emphasis on frictional heating, in the absence of axial conduction, is the subject of this presentation. As a simple example, consideration is given to the numerical study of the heat transfer in flow between two impermeable parallel plates. The individual effects of temperature change at the walls, frictional heating, and the combined effects are examined. The data shows that the combined effects can produce removable singularities under certain boundary conditions. To avoid the occurrence of singularities in these types of applications, certain heat transfer parameters are presented in different but basic forms.     

THE PHYSIOGRAPHIC FEATURES OF THE MIOCENE RAS MALAAB GROUP BASIN, SOUTH BAKR OILFIELD, GULF OF SUEZ, EGYPT

The lithostratigraphy and petrography of the Ras Malaab Group were investigated in order to define the physiography and structure of the depositional basin. The Ras Malaab Group consists, from the top, of the Zeit, South Gharib and Belayim Formations.
The basal Belayim Formation consists of carbonate barrier (reefal, lagoonal and marine tidal-flat carbonates, located from east to west respectively in the basin. Thus. reefal limestones and evaporites are associated within the succession of the Belayim Formation.
The overlying South Gharib Formation is composed of thick evaporite sediments that were deposited in a restricted, subsiding salina basin. Intense subsidence in the western part of the basin is related to faulting.
The Zeit Formation consists of evaporites and fine clastics derived from surrounding land-masses. The Zeit sequence indicates relatively deeper, semi-restricted, lagoonal conditions.     

大数据环境下的电子数据审计:机遇、挑战与方法

电子数据审计的研究与应用是近年来审计领域的热点问题。大数据时代的到来给电子数据审计带来了机遇与挑战。首先阐述了研究大数据环境下电子数据审计的重要性;然后分析了电子数据审计的内涵及原理;在此基础上,重点研究了大数据环境下电子数据审计面临的机遇与挑战,并结合大数据的特点以及目前已有的大数据分析技术与工具,探讨了大数据环境下开展电子数据审计的方法;最后给出了大数据环境下开展电子数据审计的相关建议。研究结果为今后大数据环境下开展电子数据审计提供了理论基础。     

Porous hydroxyapatite‐bioactive glass hybrid scaffolds fabricated via ceramic honeycomb extrusion

The successful fabrication of hydroxyapatite‐bioactive glass scaffolds using honeycomb extrusion is presented herein. Hydroxyapatite was combined with either 10 wt% stoichiometric Bioglass^® (BG1), calcium‐excess Bioglass^® (BG2) or canasite (CAN). For all composite materials, glass‐induced partial phase transformation of the HA into the mechanically weaker β‐tricalcium phosphate (TCP) occurred but XRD data demonstrated that BG2 exhibited a lower volume fraction of TCP than BG1. Consequently, the maximum compressive strength observed for BG1 and BG2 were 30.3 ± 3.9 and 56.7 ± 6.9 MPa, respectively, for specimens sintered at 1300°C. CAN scaffolds, in contrast, collapsed when handled when sintered below 1300°C, and thus failed. The microstructure illustrated a morphology similar to that of BG1 sintered at 1200°C, and hence a comparable compressive strength (11.4 ± 3.1 MPa). The results highlight the great potential offered by honeycomb extrusion for fabricating high‐strength porous scaffolds. The compressive strengths exceed that of commercial scaffolds, and biological tests revealed an increase in cell viability over 7 days for all hybrid scaffolds. Thus it is expected that the incorporation of 10 wt% bioactive glass will provide the added advantage of enhanced bioactivity in concert with improved mechanical stability.     

Relaxor ferroelectric-like behavior in 10PbTiO3–10Fe2O3–30V2O5–50B2O3 glass for energy storage applications

Recently, demand increased for dielectric materials used in energy storage devices at high voltage applications. Appearance of polar clusters in glass matrix could promote its use in energy storage applications. Conventional quenched glass sample of composition 10PbTiO₃–10Fe₂O₃–30V₂O₅–50B₂O₃ were successfully developed. The glassy nature was confirmed by XRD and DSC measurements. Boson peak observed at low frequency from the Raman spectra confirms polar cluster formation. Dielectric properties of prepared glass were investigated in a wide range of frequency and temperature. Broad and diffuse peak of dielectric permittivity shifted to the higher temperatures, denoting the typical relaxor ferroelectrics like behavior. Sample shows energy storage density of about 164.7 mJ/cm³ at room temperature. Quenched glass sample shows typical anti-ferromagnetic behavior.

     

Performance comparison of the mass transfer models with internal reforming for solid oxide fuel cell anodes

In this work, models describing multicomponent gas diffusion process in an electrode of a porous solid oxide fuel cell (SOFC) anode coupled with internal reforming reactions were developed. The performances of three different types of models, the dusty-gas model (DGM), the binary-friction model (BFM) and the cylindrical pore interpolation model (CPIM), were compared in 1D. All these models take into account Knudsen diffusion and molecule–molecule diffusion can be used in transition region which is generally the case in a SOFC electrode. The developed models are able to predict the fuel components’ molar fraction distributions in the anode electrode, and the concentration overpotential. They are capable of simulating the internal reforming process for hydrocarbon fuel, such as natural gas, with kinetic models considering both methane-steam reforming (MSR), and water–gas shift reaction (WSR). The effects of pressure gradient, pore size, current density, are studied. It was found that three models give similar results in difference cases using the same “tuned” tortuosity factor (τ²). The difference caused using the isobaric assumption is negligible for the H₂–H₂O–Ar and CO–CO₂ system, expect at small pore sizes (under 1 μm) and high current density (above 1 A/cm²). For a system fed with hydrocarbon fuel, the isobaric assumption will change the molar fraction distribution by up to 10% for different gas mixture components for the CPIM and the BFM, and up to 25% for the DGM at small pore sizes. However, the reaction rates for both MSR and WSR remain the same when the pressure variation is neglected.