In this work, different doping strategies for ceria were investigated in isothermal and near-isothermal cycles for solar fuel production. The system efficiency was evaluated by a more realistic model with the whole oxidation process concerned. In terms of fuel productivity, doping ions with lower valences seems to be a disadvantageous strategy due to formation of inert oxygen vacancies. Zr doped ceria exhibited the highest productivity under all of the reaction conditions investigated. The efficiency comparison of pure and Zr doped ceria is different from theoretical prediction, and the influence of oxidation rate is highlighted. The advantage of higher productivity caused by adding Zr is traded off by its drawbacks in kinetics for isothermal cycles at 1300 and 1400 °C. Benefit in efficiency only could be observed in an isothermal cycle at 1500 °C. Compared to the isothermal cycle, the near-isothermal cycle with a small temperature swing showed improvement in both fuel productivity and efficiency. Pure ceria showed better performance than 10% Zr doped ceria in 1500 °C/1300 °C near-isothermal cycles.
Supercritical water fluidized bed (SCWFB) is a promising reactor to gasify coal or biomass with low pollution. In the present paper, attempts are made to model wall-to-bed heat transfer in a SCWFB by the packet renewal theory developed in traditional fluidized beds. The key parameters, such as the packet residence time near the wall, the fraction of total time with packet contact, and packet voidage, which are required for the packet approach, are obtained by the homemade capacitance probe for high temperature and pressure. To complete the wall-to-bed heat transfer model in a SCWFB, the physical properties of the packet are chosen properly and seven kinds of thermal conductivity models for the mixture are tested. A simplified spherical particle model is adopted to describe the thermal resistance between the wall and the packet. Then, a comparison is made between heat transfer coefficients by the model based on the packet renewal theory and heat transfer coefficients by the empirical correlation [Zhang Int. J. Multiphase Flow, 2018, 109, 26−34]. It is found that they could match well with each other. The best fit can be observed when the Zehner and Schltinder thermal conductivity model is adopted, the relative error of which is 5.6% and the maximum relative error of which is less than 15%. Moreover, wall-to-packet heat transfer is considered to be dominant in a SCWFB.
Kilonovae produced by mergers of binary neutron stars (BNSs) are important transient events to be detected by time domain surveys with the alerts from the ground-based gravitational wave detectors. The observational properties of these kilonovae depend on the physical processes involved in the merging processes and the equation of state (EOS) of neutron stars (NSs). In this paper, we investigate the dependence of kilonova luminosities on the parameters of BNS mergers, and estimate the distribution functions of kilonova peak luminosities (KLFs) at the u, g, r, i, y, and z bands as well as its dependence on the NS EOS, by adopting a comprehensive semi-analytical model for kilonovae (calibrated by the observations of GW170817), a population synthesis model for the cosmic BNSs, and the ejecta properties of BNS mergers predicted by numerical simulations. We find that the kilonova light curves depend on both the BNS properties and the NS EOS, and the KLFs at the considered bands are bimodal with the bright components mostly contributed by BNS mergers with total mass $\lesssim 3.2M_\odot$/$2.8M_\odot$ and fainter components mostly contributed by BNS mergers with total mass $\gtrsim 3.2M_\odot$/$2.8M_\odot$ by assuming a stiff/soft (DD2/SLy) EOS. The emission of the kilonovae in the KLF bright components is mostly due to the radiation from the wind ejecta by the remnant discs of BNS mergers, while the emission of the kilonovae in the KLF faint components is mostly due to the radiation from the dynamical ejecta by the BNS mergers.
Supercritical water fluidized bed (SCWFB) has been used to gasify biomass, coal and solid waste to produce gas fuel. Supercritical carbon dioxide fluidized bed (SCCO2FB) was applied in the coating industry. Both the two fluidized bed treats the supercritical fluids as fluidization medium. The fluidization behaviours of particles in the supercritical fluids are quite important issues for achieving the basic two phase flow pattern. Few research institutions have conducted experimental and numerical investigations on the fluidization in supercritical conditions. The authors try to establish a comprehensive insight of fluid dynamics of the supercritical fluidized bed. For the SCWFB, the fluidization transitions of fixed bed, homogeneous bed expansion and bubbling were demarcated by discrimination number Dn. A flow pattern map of Reynolds number vs. Archimedes number was available for describing the flow patterns and their boundaries of the SCCO2FB. Ergun equation was acceptable for calculating the fixed bed pressure drop for both SCWFB and SCCO2FB. Wei and Lu correlations of the minimum fluidization velocity, minimum bubbling velocity and homogeneous bed expansion rate are suggested to design the SCWFB. Wen and Yu equation of the minimum fluidization velocity, Vogt et al. correlation of the homogeneous bed expansion rate and their method for determining the minimum bubbling velocity, Nakajima et al. equation of transition velocity, and Bi and Fan correlation of turbulent velocity were recommended to calculate SSCO2FB.
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