A lattice Boltzmann model for heat transfer in heterogeneous media

So far the lattice Boltzmann (LB) method has matured as a powerful tool to address a diversity of heat and mass transfer challenges. For most practical applications, the variation of thermophysical properties of working media will influence the performance of industrial systems substantially. However, nowadays the efforts to improve the LB method to consider variable thermophysical properties of working media are quite sparse. In the present work we firstly analyze the shortcomings of the available LB approaches for modeling working fluid with variable thermophysical properties. Based on the analysis, a simple LB model is proposed to overcome these shortcomings. The feasibility and reliability of the new LB model have been validated by three simple but nontrivial benchmark tests. Although it is originally proposed to simulate fluid flow with variable thermophysical properties, the present model can be extended directly to some other research areas where variation of thermophysical properties of working media should be considered, such as conjugate heat transfer between solid materials

Prediction of the radiative heat transfer in small and large scale oxy-coal furnaces

Predicting thermal radiation for oxy-coal combustion highlights the importance of the radiation models for the spectral properties of gases and particles. This study numerically investigates radiation behaviours in small and large scale furnaces through refined radiative property models, using the full-spectrum correlated k (FSCK) model and Mie theory based data, compared with the conventional use of the weighted sum of grey gases (WSGG) model and the constant values of the particle radiation properties. Both oxy-coal combustion and air-fired combustion have been investigated numerically and compared with combustion plant experimental data. Reasonable agreements are obtained between the predicted results and the measured data. Employing the refined radiative property models achieves closer predicted heat transfer properties to the measured data from both furnaces. The gas-phase component of the radiation energy source term obtained from the FSCK property model is higher within the flame region than the values obtained by using the conventional methods. The impact of using non-grey radiation behaviour of gases through the FSCK is enhanced in the large scale furnace as the predicted gas radiation source term is approximately 2-3 times that obtained when using the WSGG, while the same term is in much closer agreement between the FSCK and the WSGG for the pilot-scale furnace. The predicted total radiation source term (from both gases and particles) is lower in the flame region after using the refined models, which results in a hotter flame (approximately 50-150 K higher in this study) compared with results obtained from conventional methods. In addition, the predicted surface incident radiation reduces by using the refined radiative property models for both furnaces, in which the difference is relevant with the difference in the predicted radiation properties between the two modelling techniques. Numerical uncertainties resulting from the influences of combustion model, turbulent particle dispersion and turbulence modelling on the radiation behaviours are discussed

Speciation of Metals and Assessment of Contamination in Surface Sediments from Daya Bay, South China Sea

The contents, speciation, source factors and potential ecological risks of the selected metals (Cr, Ni, Cu, Pb, Zn, Cd and As) were analyzed in surface sediments from Daya Bay (DYB). The results show that, with the exception of Pb, metal concentrations have decreased at all sites over the past decade. The distribution features of these concentrations represent a ring shape that descends from shore to bay by varying degrees. Speciation analysis showed that Cr, Ni, Cu, Zn and As exist mainly in the residual fraction and, thus, are of low bioavailability, while Cd and Pb were found to be abundant in the non-residual fraction and, thus, have high potential mobility. The ratio of heavy metals in non-residual form in descending order is Pb (78.83%), Cd (78.65%), Cu (48.54%), Zn (48.10%), Ni (38.31%), Cr (28.43%) and As (27.76%). The ratio of Pb content is the highest, meaning the highest mobility of Pb. The metals’ potential ecological risks to the environment were also assessed using the methods of the mean effect range-median quotient and the criteria of risk assessment code. The results showed that Cd presents the highest risk, and Pb and Cu are generally considered to be medium risks in the sub-basins of Daya Bay. The principal component analysis (PCA) revealed that natural coastal weathering and erosion of rock caused the highest input, followed by mariculture and industrial wastewater and, finally, domestic sewage discharge

DFT and Experimental Study on the Mechanism of Elemental Mercury Capture in the Presence of HCl on α‑Fe₂O₃(001)

To investigate the mechanism of Hg⁰ adsorption on the α-Fe₂O₃(001) surface in the presence of HCl, which is considered to be beneficial for Hg⁰ removal, theoretical calculations based on density functional theory as well as corresponding experiments are carried out. HCl adsorption is first performed on the α-Fe₂O₃(001) surface, and the Hg⁰ adsorption on HCl-adsorbed α-Fe₂O₃(001) surface is subsequently researched, demonstrating that HCl dissociates on the surface of α-Fe₂O₃, improving the Hg⁰ adsorption reactivity. With further chlorination of the α-Fe₂O₃(001) surface, FeCl₃ can be achieved and the adsorption energy of Hg⁰ on the FeCl₃ surface reaches −104.2 kJ/mol, representing strong chemisorption. Meanwhile, a group of designed experiments, including Hg⁰ adsorption on HCl-preadsorbed α-Fe₂O₃ as well as the coadsorption of both gaseous components, are respectively performed to explore the pathways of Hg⁰ transformation. Combining computational and experimental results together, the Eley–Rideal mechanism with HCl preadsorption can be determined. In addition, subsequent X-ray photoelectron spectroscopy analysis verifies the appearance of Cl species and oxidized mercury, exhibiting the consistency with experiments

A novel source/drain on void (SDOV) MOSFET implemented by local co-implantation of hydrogen and helium

In this paper a novel device named as SDOV MOSFET is proposed for the first time. This structure features localized void layers under the source and drain regions. The short channel effects of this device can be improved due to the SOI-like source/drain structure. In addition, witliout the dielectric layer under the channel region, this device can avoid some weaknesses of UTB SOI devices caused by the thin silicon film and the underlying buried oxide, such as mobility degradation, film thickness fluctuation and self-heating effect. Based on self-aligned hydrogen and helium co-implantation technology, the new device can be fabricated by a process compatible with the standard CMOS process. The SDOV MOSFETs with 50 nm gate length are experimentally demonstrated for verification. (C) 2008 Elsevier B.V. All rights reserved

Remote sensing of particulate organic carbon dynamics in a eutrophic lake (Taihu Lake, China)

A two step approach was developed to estimate POC concentrations in a shallow eutrophic lake, where dissolved carbon and inorganic particulate matter strongly influence optical properties. The approach was based on the identification of a co-variability of POC concentrations with one or more inherent optical properties (IOPs). In the present case, a relationship between POC and absorption at 620nm was identified and was combined with a reflectance based algorithm for case II waters. Compared with other published POC algorithms, this approach provided better estimates over a wide range of POC concentrations in two hypereutrophic lake waters with the predominance of cyanobacteria (R2>0.80). While it is unlikely that a single POC algorithm can be created that is independent of the variability of POC sources, this approach allows for a common method to identify appropriate algorithms with which POC dynamics can be explored