A generalized analysis on material invariant characteristics for microwave heating of slabs

A generalized dimensionless formulation has been developed to predict the spatial distribution of microwave power and temperature. The ‘dimensionless analysis’ is mainly based on three numbers: wave number, ; free space wave number, ; and penetration number, , where is the ratio of sample thickness to wavelength of microwaves within a material, is based on wavelength within free space and is the ratio of sample thickness to penetration depth. The material dielectric properties and sample thicknesses form the basis of these dimensionless numbers. The volumetric heat source due to microwaves can be expressed as a combination of dimensionless numbers and electric field distributions. The spatial distributions of microwave power for uniform plane waves can be obtained from the combination of transmitted and reflected waves within a material. Microwave heating characteristics are obtained by solving energy balance equations where the dimensionless temperature is scaled with respect to incident microwave intensity. The generalized trends of microwave power absorption are illustrated via average power plots as a function of , and . The average power contours exhibit oscillatory behavior with corresponding to smaller for smaller values of . The spatial distributions of dimensionless electric fields and power are obtained for various and . The spatial resonance or maxima on microwave power is represented by zero phase difference between transmitted and reflected waves. It is observed that the number of spatial resonances increases with for smaller regimes whereas the spatial power follows the exponential decay law for higher regimes irrespective of and . These trends are observed for samples incident with microwaves at one face and both the faces. The heating characteristics are shown for various materials and generalized heating patterns are shown as functions of , and . The generalized heating characteristics involve either spatial temperature distributions or uniform temperature profiles based on both thermal parameters and dimensionless numbers ().     

Electrochemical performances of gel polymer electrolytes using tetra(ethylene glycol) diacrylate

A gel polymer electrolyte (GPE) was prepared using tetra(ethylene glycol) diacrylate monomer, benzoyl peroxide, and (). The LiCoO₂/GPE/graphite cells were prepared and their electrochemical properties were evaluated at various current densities and temperatures.The viscosity of the precursor containing the tetra(ethylene glycol) diacrylate monomer was around . The ionic conductivity of the gel polymer electrolyte at 20°C was around . The gel polymer electrolyte had good electrochemical stability up to vs. Li/Li⁺. The capacity of the LiCoO₂/GPE/graphite cell at rate was 63% of the discharge capacity at rate. The capacity of the cell at −10°C was 81% of the discharge capacity at 20°C. Discharge capacity of the cell with gel polymer electrolyte was stable with charge-discharge cycling.     

A kinetic study on anaerobic reduction of sulphate, part II: incorporation of temperature effects in the kinetic model

The effects of temperature on the kinetics of anaerobic sulphate reduction were studied in continuous bioreactors using acetate as an electron donor. Across the range of temperatures applied from 20 to , the increasing of volumetric loading rate up to 0.08 to resulted in a linear increase in reduction rate of sulphate. The increasing reaction rate showed a lower dependence on volumetric loading rate in the range 0.1-. Further increase in volumetric loading rate above was accompanied by wash out of bacterial cells and a sharp decrease in reaction rate. Despite a similar pattern for dependency of reaction rate on volumetric loading at all temperatures tested, the magnitude of reaction rate was influenced by temperature, with a maximum rate of observed at . The effect of temperature on maximum specific growth rate (μ_max) and bacterial yield was insignificant. The values of maximum specific growth rate and yield were and 0.56-0.60 kg bacteria (), respectively. The decay coefficient (k_d) and apparent saturation constant () were both temperature dependent. The increase of temperature resulted in decreased values of , and higher values for k_d. Using the experimental data effect of temperature was incorporated in a kinetic model previously developed for anaerobic reduction of sulphate.     

The effect of magnetic fields on the electrodeposition of cobalt

The effect of a magnetic field on the electrodeposition of Co has been investigated with respect to the strength and the orientation of the magnetic field (B). Two different effects of the magnetic field B on the electrodeposition of cobalt have been observed. The first is the magnetohydrodynamic (MHD) effect caused by the Lorentz force (). The second is an effect due to the paramagnetic force (), caused by the concentration gradient () and therefore the gradient of the molar susceptibility (). The limiting current density and the deposition rate of Co increases if the B-field is oriented parallel to the electrode surface. This is mainly due to the expected convection induced by . Both, the Co deposition and the reduction of hydrogen ions, are affected by this. At high cathodic potentials the contribution of the hydrogen reduction to the process changed, which led to homogeneous deposits. A decreasing deposition rate was measured for B-fields oriented parallel or antiparallel to the flow of ions. These results are attributed to the effect of on the electrochemical processes close to the surface.     

A new method to determine the microbial kinetic parameters in biological air filters

This paper presents a new method to determine kinetic parameters of the biodegradation of various pollutants in a biofilter. Toluene, a readily biodegradable volatile organic compound, and methane, a hydrocarbon and a greenhouse gas, have been chosen as the target pollutants. The new protocol utilized biomass immobilized on bed pellets; these directly sampled from a continuous steady-state biofilter. The comparison of this method with the conventional experimental protocol utilizing micro-organisms suspended in a liquid medium was made using the pollutant toluene. Indeed, with both methods, the kinetic parameters have been evaluated by following the microbial growth in batch, thermostated reactors, using determined amounts of pollutant substrate. This experiment has confirmed the pertinence of the new procedure. The interesting features of the new method are that: (1) it is easy to operate (no preliminary treatment of the bed samples) and (2) it provides reproducible parameters that represent the real biofilter case more adequately than liquid cultures. In addition, modeling of the experimental specific growth rates in the case of toluene has shown that the values obtained with the use of solid extracts can be correlated by a Haldane's formulation, where , , and . The maximum specific growth rate was reached for an initial concentration of toluene near . The determination of the experimental specific growth rates of micro-organisms in the methane biofilter has also been performed. This study allowed highlighting two methane concentrations’ ranges: from 1000 to 14 500 ppmv and from 14 500 to 27 000 ppmv. For the first range, the Monod model proves to be suitable with the kinetic parameters: and . For the second range, neither the Monod nor the Haldane's formulation could directly be used. However, a mathematical adjustment of the Monod model allows to find kinetic parameters and . The biomass yields for the tested methane concentrations have also been determined and showed two different tendencies, depending on the same two ranges. For the first range of methane concentrations, the biomass yield was quite constant with an average value around while for the second range, it could be approached by a polynomial second-order regression. The maximum value of the biomass yield obtained on the second range was at a methane initial concentration of 20 000 ppmv.     

Temperature variations in the oxygen carrier particles during their reduction and oxidation in a chemical-looping combustion system

A particle reaction model including mass and heat transfer has been developed to know the temperature variations produced inside the oxygen carrier particles during the cyclic reduction and oxidation reactions taking place in a chemical-looping combustion (CLC) system. The reactions of the different oxygen carriers based on Cu, Co, Fe, Mn, and Ni during the reduction with fuel gas (CH₄, CO, and H₂) and oxidation (O₂) have been considered. In these systems, the oxidation reaction is always exothermic with subsequent heat release; however, the reduction reaction can be exothermic or endothermic depending on the metal oxide and the fuel gas. The heat generated inside the oxygen carriers during the exothermic reactions increases the particle temperature, and could affect the particle structure if the temperature increase is near to the melting point of the active materials. Several variables that affect the reaction rate and the heat transport process have been analyzed to know their effect on the internal particle temperature. For a given oxygen carrier and reaction, the maximum temperature of the particles depended mainly on the particle size, the reaction rate, and the external heat transfer resistance, being lower than the effect of the oxygen carrier porosity, type of inert material, and metal oxide content. The highest temperature variations were reached for the oxidation reactions, with the maximum corresponding to the Ni and Co oxygen carriers with values of for particles. The highest temperature increase observed during the reduction reactions corresponded to the reaction of CuO with CO, with values of for particles. For the rest of the reactions and metals, the variations in the particle temperature were below for particle sizes below . Under the typical operating conditions that exist in a CLC system, with particle sizes lower than , % of metal oxide content, and overall conversion times lower than , the increases of temperature with respect to the bulk conditions were lower than for any reaction of any oxygen carrier. Moreover, the temperature profiles inside the particles were near flat in most of the practical conditions, and no local points with high temperatures were found. Thus, changes in the solid porous structure of the carrier due to sintering during oxidation in fluidized bed reactors are not expected working at typical temperatures of CLC systems (1000-).