Reduced-order model for redox kinetics of oxygen carrier in chemical looping combustion

A reduced-order model was developed to calculate the redox kinetics of oxygen carrier in chemical looping combustion. The reduced-order model can describe the major physical/chemical features of the redox steps of oxygen carrier, such as gas diffusion around and inside the particle, surface reaction, product growth, product layer diffusion, pore structure change etc. It is an analytical model simplified using the Thiele modulus method and thus is much easier for computational fluid dynamics modeling and reactor design. The accuracy of variations of redox conversion under different temperatures and gas concentrations predicted by the reduced-order model is verified by comparison with both the detailed one-dimensional model and the experimental data. The results indicate that the reduced-order model can reproduce the prediction accuracy of the detailed one-dimensional model and agrees well with the experimental data. The well observed two-stage behavior of a fast initial stage followed by a second slower stage was discussed in detail. Further, the reduced-order model was used to analyze the effect of particle structural parameters on the kinetics. The relative importance of each controlling step in the kinetics of oxygen carrier predicted by the reduced-order model was compared.     

Microwave absorption of oxygen measured with a Fabry-Perot spectrometer

A Fabry-Perot interferometer in the semiconfocal configuration has been used as a microwave spectrometer by the method of Q-reduction. The Q can be determined with conventional laboratory equipment to within 2% accuracy, corresponding to 0.3 dB/km at 58.82 GHz. Absolute of pure oxygen and dry air at fixed frequencies has been measured as a function of pressure from 0 to 1 atm at room temperature. The measured absorption of dry air can be explained if the overlap of the oxygen lines is properly taken into account.     

Differential scanning calorimetry and a thermogravimetric analysis of nanozirconia-based powder systems

Results obtained from differential scanning calorimetry and a thermogravimetric analysis of zirconia-based nanocrystalline powder systems are presented. Heating is found to cause intense mass loss that increases with increase in the MgO content. Differential scanning calorimetry has revealed that the total energy expended for reactions involved in the powder heating process increases with increase in the MgO content. The heated powders are characterized by desorption of water. For 10 wt. % MgO, residual nitrates are seen to decompose into NO₂, N₂O, or NO.     

Design sensitivity analysis of a system under intact conditions using measured response data

Design sensitivity requires knowledge of the accurate characteristics of system dynamics to determine the solution parameters—eigenvalues or eigenvectors. This paper presents a new form of sensitivity analysis based on transmissibility functions that can indicate the appropriate candidate node for minimal design modification. The proposed sensitivity analysis uses only measured response data and is performed under intact conditions without any system identification. The feasibility of the proposed sensitivity analysis is first verified through both an experiment and a computer-aided analysis of the uniaxial vibration of a notched beam; then its methodology is investigated by simulation involving a 5-degrees-of-freedom system.     

Synthesis of lanthanum nickelate perovskite nanotubes by using a template-inorganic precursor

A new route to obtain metal oxide nanotubes is presented: an inorganic coordination complex precursor containing the metal ions and impregnated into alumina membrane templates yield hollow tubular nanostructures of LaNiO₃ by calcination at 600 °C as characterized by powder X-ray diffraction (XRD). Scanning electron microscopy (SEM) shows that the resulting nanotubes have 200 nm in diameter in good agreement with the template pore. Transmission electron microscopy (TEM) and dark field transmission electron microscopy (DF-TEM) show that the nanotubes with 10-20 nm walls and internal separations are composed of 3-5 nm crystals.     

透射光栅谱仪测谱不确定度分析

透射光栅谱仪广泛应用于惯性约束聚变和其他激光等离子体相互作用领域. 而辐射光谱的精确测量依赖于测量设备的不确定度. 本文从标定过程出发, 分析了标定实验对透射光栅各级衍射效率带来的不确定度. 结合标定实验带来的不确定度, 分析了实验结果解谱过程带来的不确定度. 给出了0.1-5keV能段测量光谱的不确定度. 关键词： 不确定度 透射光栅 实验标定     

Titration of gases with oxygen using a zirconia oxygen pump-gauge

Using the zirconia pump-gauge composed of a zirconia oxygen pump and a zirconia oxygen sensor, flowing gases can be titrated with oxygen in a similar way to the pH titration in aqueous solutions. A review is presented on theoretical and experimental results for the gas titration obtained in our laboratory. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15–21, 2002.     

Mechanism and kinetics of lithium vapor capture in a high-temperature packed bed of kaolinite

This study investigated the characteristics of high-temperature lithium vapor-capturing reaction in a packed bed of calcined kaolin particles. The packed-bed sorption experiments were carried in the a temperature range of 700-900 °C. The high-temperature reaction between LiCl vapor and calcined kaolin sorbent generated lithium aluminum silicate (Li₂O·Al₂O₃·2SiO₂). An increase in kaolin bed temperature results in an increase in lithium-capturing rate, but it has no effect on the maximum lithium uptake. The resistance of LiCl vapor diffusion into the pores of calcined kaolin particles was negligible, and the chemical reaction at the kaolin surface controlled the overall sorption reaction rates by up to 60% of metakaolinite conversion. The order of the reaction between metakaolinite and LiCl vapor was determined as 1.94 and its activation energy was estimated as 7.95 kcal/mol according to the Arrhenius relationship.     

Interpretation of a layer mechanical impedance measured using a hard round die

Theoretical expressions for the impedance characteristics of a layer bound to a rigid base are obtained for various profiles of the normal pressure under a die that vibrates on the layer surface without producing any shear stresses. The frequency dependences of the impedance characteristics of a homogeneous gelatin layer and their variation with changes in the die diameter are measured by means of a specialized software-hardware system. The impedance characteristics are calculated for the models with “uniform,” “parabolic,” and “hyperbolic” pressure profiles under the die, and the results are compared with the experimental data. The model with a uniformly distributed pressure under the die is found to be the most adequate one.     

On the kinetics of oxygen adsorption on a Pt(111) surface

The kinetics of O₂ adsorption on a clean Pt(111) surface were investigated in the temperature range 214–400°C. The oxygen coverage was measured by CO titration as well as Auger electron spectroscopy both of which show the same dependence on O₂ exposure. The initial sticking coefficient on clean Pt(111) is 0.08–0.10 and decreases exponentially with increasing oxygen coverage. For θ > 0.23 a (2 × 2)-O LEED pattern was observed. The highest oxygen coverage obtained was approximately 0.45. A theoretical model was proposed which correlates the coverage dependence of the sticking coefficient with adsorbate interactions in the chemisorbed state. These interactions cause a coverage dependent activation energy of adsorption assuming the existence of a precursor state. Experiments dealing with the effect of carbon contamination on the sticking coefficient showed that the initial sticking coefficient decreases with increasing carbon coverage.     

Passive ranging of a moving sound source using three-dimensional measured information

To solve the problem of passive ranging of a moving sound source,a method of estimating the initial distance of target is presented by using the measured inform...     

The order with respect to oxygen and the activation energy for the burning of an anthracitic char in O2 in a fluidised bed, as measured using a rapid analyser for CO and CO2

Measurements of the oxidation of a coal char in a fluidised bed have the advantages that the rates of heat and mass transfer to and from a reacting particle are large and characterised well. However, problems have arisen from a combination of the slow, but typical, response–time (4 s) of the analysers for CO and CO₂ and the slow mixing of gases when filling a fairly large fluidised bed. The resulting time constant for the sampling system was 8 s and comparable to the time for combustion at 900 °C or above. The purpose of this work was to measure the kinetics of oxidation of a char in a smaller fluidised bed (with a shorter mixing time) using an analyser for CO and CO₂ with a response time as low as 0.1 s. The result is that the oxidation of an anthracitic char is now found to be first order in O₂ between 700 and 900 °C; at 900 °C the order previously measured was almost zero. The activation energy is now measured here to be 145 ± 25 kJ/mol, in agreement with some early work.     

Wavelet analysis of digital shearing speckle patterns with a temporal carrier

Shearography is an optical technique allows direct measurement of deflection derivatives. This paper presents a novel temporal phase analysis technique based on wavelet transform when shearography is applied to measure a continuously deforming object. A series of shearing speckle patterns is captured by a high-speed camera during the deformation. To avoid the phase ambiguity problem, a temporal carrier is generated by a piezoelectrical transducer (PZT) stage in one beam of the modified Michelson interferometer. The intensity variation of each pixel on recorded images is then analyzed along time axis by a robust mathematical tool - complex Morlet wavelet transform. After the temporal carrier is removed, the absolute phase change representing the first-order derivative of the continuous deformation is obtained without the need of temporal or spatial phase unwrapping process. The results obtained by wavelet transform are compared with those from temporal Fourier transform.     

Synthesis and characterization of a nano-scaled barium cerate perovskite powder using starch as polymerization agent

The preparation of nano-sized BaCeO₃ powder using starch as a polymerization agent is described herein. Phase evolution during the decomposition process of a (BaCe)-gel was monitored by XRD. A phase-pure nano-sized BaCeO₃ powder was obtained after calcining of the (BaCe)-gel at 920 °C. The resulting powder has a specific surface area of 15.4 m²/g. TEM investigations reveal particles mainly in the size range of 30 to 65 nm. The shrinkage and sintering behavior of resulting powder compacts were studied in comparison to a coarse-grained mixed-oxide BaCeO₃ powder (S_BET = 2.1 m²/g). Dilatometric measurements show that the beginning of shrinkage of compacts from the nano-sized powder is downshifted by 300 °C compared to mixed-oxide powder. Compacts from the nano-sized powder reach a relative density of 91% after sintering at 1450 °C for 10 h.     

Ordering of oxygen vacancies in a CaMnO<Subscript>3 − δ</Subscript> perovskite single crystal

The structure of a CaMnO_{3 ? δ} perovskite single crystal was studied for the first time using thermal neutron diffraction in the temperature range 300–840 K. It was detected that oxygen vacancies in the crystal are ordered into two types of superstructure. A phase with a relative number of vacancies δ = 1/4 occupies the largest volume fraction of oxide (～75%); the other volume is occupied by a superstructure with a lower vacancy content (δ = 1/5). The oxygen deficiency in the crystal lattice was determined to be δ = 0.238. The mechanism of oxygen vacancy ordering in the oxide is discussed taking into account its charge state.     

Fast simulation of second harmonic ultrasound field using a quasi-linear method

Nonlinear propagation of sound has been exploited in the last 15 years in medical ultrasound imaging through tissue harmonic imaging (THI). THI creates an image by filtering the received ultrasound echo around the second harmonic frequency band. This technique produces images of enhanced quality due to reduced body wall reverberation, lower perturbations from off-axis echoes, and multiple scattering of reduced amplitude. In order to optimize the image quality it is essential to be able to predict the amplitude level and spatial distribution of the propagating ultrasound pulse. A method based on the quasi-linear approximation has been developed to quickly provide an estimate of the ultrasound pulse. This method does not need to propagate the pulse stepwise from the source plane to the desired depth; it directly computes a transverse profile at any depth from the definitions of the transducer and the pulse. The computation handles three spatial dimensions which allows for any transducer geometry. A comparison of pulse forms, transverse profiles, as well as axial profiles obtained by this method and state-of-the-art simulators, the KZKTexas code, and Abersim, shows a satisfactory match. The computation time for the quasi-linear method is also smaller than the time required by the other methods.     

Isothermal reduction kinetics of nickel oxide using hydrogen: Conventional and Weibull kinetic analysis

The powder sample of nickel oxide was synthesized by sol-gel procedure. The isothermal reduction of nickel oxide using hydrogen was investigated by thermogravimetric analysis at five operating temperatures: 245, 255, 265, 275 and 300 °C. The kinetic triplet (E_a, A and f(α)) was determined using conventional and Weibull kinetic analysis. Both the kinetically procedures show that the reduction process considered can be explained with a two-step kinetic model. It is established that at lower temperatures (245 °C?T?255 °C), the reduction process considered is governed by two-parameter Šesták-Berggren autocatalytic model (first step) and at higher temperatures (T?265 °C), the reduction process is governed by Fn reaction model with different values of parameter n (second step). In this paper, the complex manner of dependence of the Weibull shape parameter (β) on temperature is established. With alterations of Weibull shape parameter from lower temperatures (β>1) to higher temperatures (β<1), it was concluded that isothermal reduction process of NiO using hydrogen can be described by a multistep reaction mechanism. These results are confirmed by the evaluated density distribution functions (ddf) of apparent activation energies (E_a), which show variations in basic characteristics at lower and higher operating temperature regions. Also, in this paper, it was shown that the shape parameter (β) of Weibull distribution function can represent the behaviour index, which indicates the kinetic pattern of the mechanism controlling the process studied.     

Two-photon excitation of atomic oxygen using a Raman-shifted ArF-excimer laser

A novel method for exciting the two-photon 2p ³ 3p ³ P 2p ^{4 3} P atomic oxygen transition is reported. The transition energy is provided by the combined photon energies of the second and third Stokes orders of a deuterium-filled Raman shifter pumped by an ArF-excimer laser. The ArF-excimer-pumped Raman shifter performance is characterized and the approach is demonstrated in an atomic oxygen population created by molecular oxygen absorption and predissociation in room air.