A simple model for predicting solid concentration distribution in binary‐solid liquid fluidized beds

A simple mathematical model for predicting the solid concentration profile in binary‐solid liquid fluidized beds is presented. The main assumption is that the solid concentration distribution follows the logistic function, which is supported by the literature. Various equations have been derived to solve key system quantities (e.g., bed expansion height, length and position of the transition zone). In contrast to previous models that often involve adjustable parameters and strongly rely on the availability of experimental data, the present model only requires inputs of fluid and particle properties, operating conditions, and correlations for dispersion and slip velocity. The results showed that the model is applicable to different binary‐solid systems that have size and/or density differences. The model's capability of predicting the layer inversion phenomenon has also been demonstrated. The model is simple but proves capable of accurately predicting key information for the design, operation and scale up of liquid fluidized beds. © 2016 American Institute of Chemical Engineers AIChE J, 63: 469–484, 2017     

A Frequency Selective Surface With Miniaturized Elements

We demonstrate a new class of bandpass frequency selective surface (FSS), the building block of which, unlike the traditional FSSs, makes use of resonant dipole and slot structures that have dimensions much smaller than the operating wavelength. This design allows localization of bandpass characteristics to within a small area on the surface which in turn facilitates flexible spatial filtering for an arbitrary wave phasefront. The proposed FSS is made up of periodic array of metallic patches separated by thin air-gaps backed by a wire mesh having the same periodicity (Ltlambda). The array of metallic patches constitute a capacitive surface and the wire mesh a coupled inductive surface, which together act as a resonant structure in the path of an incident plane wave. Like traditional FSSs, the capacitive and inductive surfaces of the proposed FSS can easily be fabricated using printed circuit technology on both sides of microwave substrates. It is shown that by cascading such bandpass surfaces in a proper fashion, any arbitrary multipole filter or non-commensurate multiband response can be obtained. The frequency response of the proposed miniaturized-element frequency selective surface (MEFSS) is demonstrated for various incident angles and it is shown that one-pole designs are less sensitive than two-pole designs to the angle of incidence. Dual band designs are also possible based on two-pole designs, but are more sensitive to incident angle than single band designs because of their larger (in terms of wavelengths) spacing. Prototypes of single-pole and dual-pole MEFSSs are fabricated and tested in a waveguide environment at X-band frequencies and excellent agreements between the measured and simulated results are demonstrated     

A compact antenna for ultrawide-band applications

A novel compact and ultrawide-band (UWB) antenna is presented in this paper. The basis for achieving such an UWB operation is through proper magnetic coupling of two adjacent sectorial loop antennas in a symmetrical arrangement. A large number of coupled sectorial loop antennas (CSLA) with different geometrical parameters are fabricated and their measured responses are used to experimentally optimize the geometrical parameters of the antenna for achieving the maximum bandwidth. Through this optimization process an antenna with a VSWR of lower than 2.2 (S/sub 11/<-8.5 dB) across an 8.5:1 frequency range is designed. The maximum dimension of this antenna is smaller than 0.37/spl lambda//sub 0/ at the lowest frequency of operation and provides an excellent polarization purity. Furthermore, the antenna exhibits a relatively consistent radiation pattern. Modified versions of the CSLA are also designed to reduce the overall metallic surface and weight of the antenna while maintaining its wide-band characteristics. This allows modifying its dimensions to design low frequency light-weight UWB antennas.     

Short Communication: application of a surrogate material in assessing the impact of porosity on re‐ignition of wood‐based materials

Re‐ignition behaviour of charred solid fuels after extinction by water is studied. In this communication the effect of material porosity on re‐ignition is investigated. A surrogate ceramic material is used so as to separate the pyrolysis and combustion processes from those associated with heat transfer. Experimental data are reported for different sample thickness and porosity, and varying heat flux and water application time. Copyright © 2002 John Wiley & Sons, Ltd.     

Effect of addition of hydrophobic nano silica on viscoelastic properties and scratch resistance of an acrylic/melamine automotive clearcoat

Scratches are a consequence of tribological events encountered by automotive coatings during their service lives. A series of analytical techniques such as laboratory carwash simulator, nano-indentation, tensile, DMTA, SEM, etc. were used in order to compare the effects of addition of various contents of a nano silica on changes in the viscoelastic properties and scratch morphologies of the resultant clearcoats. The results illustrate, that incorporating increased amounts of hydrophobic nano silica particles into an automotive clearcoat decreased its T_g whilst increasing its toughness. Increasing nano silica content also gave progressive transitions from fracture type scratches to plastic type scratches.     

An overview on oxyfuel coal combustion—State of the art research and technology development

Oxyfuel combustion is seen as one of the major options for CO₂ capture for future clean coal technologies. The paper provides an overview on research activities and technology development through a fundamental research underpinning the Australia/Japan Oxyfuel Feasibility Project. Studies on oxyfuel combustion on a pilot-scale furnace and a laboratory scale drop tube furnace are presented and compared with computational fluid dynamics (CFD) predictions. The research has made several contributions to current knowledge, including; comprehensive assessment on oxyfuel combustion in a pilot-scale oxyfuel furnace, modifying the design criterion for an oxy retrofit by matching heat transfer, a new 4-grey gas model which accurately predicts emissivity of the gases in oxy-fired furnaces has been developed for furnace modelling, the first measurements of coal reactivity comparisons in air and oxyfuel at laboratory and pilot-scale; and predictions of observed delays in flame ignition in oxy-firing.     

Expansion behaviour of a binary solid-liquid fluidised bed with different solid mass ratio

This study reports the effect of particle mass compositions on the bed expansion behaviour of a binary solid liquid fluidised bed (SLFB) system. Experiments were performed comprising equal density (2230 kg m^?3) spherical glass beads particles of diameter 3, 5 and 8 mm and water as fluidising medium with different particle mass ratios varying from 0.17 to 6.0. In the expanded bed, both segregated and intermixed zones were observed depending on the different particle diameter combinations. In a completely segregated SLFB, the bottom monosized layer exhibited a negative deviation ～23% whereas a positive deviation ～25% was found in the top monosized layer when compared with the corresponding pure monosized system. A small mixing zone spanning approximately two particle diameters thick was observed to exist even in a completely segregated SLFB for higher diameter ratio cases. A slight decrease in the mixing zone height was noted with increasing liquid superficial velocity. For lower diameter ratio cases, a relatively lager mixing zone height was observed which increased with increasing liquid superficial velocity. The bed expansion ratio was noted to decrease with increasing solid mass ratio however it increased with increase in the fluidising velocity ratio following a reasonable power law trend. The expanded bed height of the binary mixture was not entirely additive of its corresponding mono-component bed heights and both positive and negative deviations were observed. Finally, a two-dimensional (2D) Eulerian-Eulerian (E-E) model incorporating the kinetic theory of granular flow (KTGF) was used to quantify the binary system hydrodynamics. The model predicted expanded bed height agreed with experimental measurements within ±6% deviation. Presence of a mixing zone was also confirmed by the CFD model and simulated particle phase volume fraction distribution qualitatively agreed with the experimental visualisations.     

Oxygen adsorption and desorption characteristics of LSCF5582 membranes for oxygen separation applications

This study examines the oxygen adsorption and desorption characteristics of La_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ (LSCF5582) membranes prepared at sintering temperatures of 1200–1300 °C, with the aim of gaining an insight into their performance in the surface reaction limited regime for oxygen separation applications. The findings of this work are then compared with our experimental data on Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ (BSCF5582) membranes. It is demonstrated that the adsorption rate constants of both membranes are two orders of magnitude greater than their respective oxygen desorption rate constants as the oxygen adsorption occurs in less than 24 s whilst the oxygen desorption takes approximately one hour to reach equilibrium. The activation energy for oxygen adsorption of LSCF5582 reduced to a quarter of its value with increasing the sintering temperature from 1200 °C to 1300 °C. This is attributed to the oxygen exchange occurring more rapidly along the grain boundaries resulting in a lower activation energy. The LSCF5582 grain sintered at 1200 °C is the optimum selection for oxygen separation applications at an operating temperature of 850 °C and oxygen partial pressure of 0.21 bar.     

A PROCESS FOR DISPOSAL OF HALON 1301 (CBrF3)

We report the results of an experimental and kinetic modeling study of gas-phase reaction between methane and halon 1301 (CBrF³). At 1000 K, with an equimolar feed of CH⁴ and CBrF³ and at a residence time of 1 second, CHF³ and CH³Br are produced at selectivities in excess of 90%. Other reaction products detected include C²H²F², C²H², C²H², and CHBrF². Very good agreement between kinetic modeling and experimental results was obtained.