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In the transporting square nosed slugging fluidization regime () a bed of polyethylene powder with a low density () and a large particle size distribution () was operated in two circulating fluidized bed systems (riser diameters 0.044 and 0.105 m). A relation was derived for the plug velocity as a function of the gas velocity, solids flux, riser diameter, particle size range and particle and powder properties. The influence of the plug length on the plug velocity, the raining rate of solids onto and from the plugs and the influence of the particle size range on the plug velocity is accounted for.  相似文献   

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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 ().  相似文献   

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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 (μmax) 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 (kd) and apparent saturation constant () were both temperature dependent. The increase of temperature resulted in decreased values of , and higher values for kd. Using the experimental data effect of temperature was incorporated in a kinetic model previously developed for anaerobic reduction of sulphate.  相似文献   

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The effect of magnetic fields on the electrodeposition of cobalt   总被引:1,自引:0,他引:1  
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.  相似文献   

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Many commercial processes for the removal of carbon dioxide from high-pressure gases use aqueous potassium carbonate systems promoted by secondary amines. This paper presents thermodynamic and kinetic data for aqueous potassium carbonate promoted by piperazine. Research has been performed at typical absorber conditions for the removal of CO2 from flue gas.Piperazine, used as an additive in 20- potassium carbonate, was investigated in a wetted-wall column using a concentration of at 40-80°C. The addition of piperazine to a potassium carbonate system decreases the CO2 equilibrium partial pressure by approximately 85% at intermediate CO2 loading. The distribution of piperazine species in the solution was determined by proton NMR. Using the speciation data and relevant equilibrium constants, a model was developed to predict system speciation and equilibrium.The addition of piperazine to potassium carbonate increases the rate of CO2 absorption by an order of magnitude at 60°C. The rate of CO2 absorption in the promoted solution compares favorably to that of MEA. The addition of piperazine to potassium carbonate increases the heat of absorption from 3.7 to . The capacity ranges from 0.4 to for PZ/K2CO3 solutions, comparing favorably with other amines.  相似文献   

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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.  相似文献   

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IR optical properties of Pd nanoparticles with different size and aggregation state were studied in the current paper. The dispersed Pd nanoparticles () stabilized with poly(N-vinylpyrrolidone) (PVP) were synthesized by the seeding growth method, in which the seeds were formed step by step through reducing H2PdCl4 with ethanol. The dispersed Pd nanoparticles of much large size () were grown from the by keeping the colloid of undisturbed for 150 days at room temperature around 20 °C. The aggregates of () were prepared through an agglomeration process induced during a potential cyclic scanning between −0.25 V and 1.25 V for 20 min at a scan rate of 50 mV s−1. Scanning electron microscope (SEM) patterns confirmed such aggregation of . Fourier transform infrared (FTIR) spectroscopy together with CO adsorption as probe reaction was employed in studies of IR optical properties of the prepared Pd nanoparticles. The results demonstrated that CO adsorbed on films substrated on CaF2 IR window or glassy carbon (GC) electrode yielded two strong IR absorption bands around 1970 cm−1 and 1910 cm−1, which were assigned to IR absorption of CO bonded on asymmetric and symmetric bridge sites, respectively. Similar IR bands were observed in spectra of CO adsorbed on films, except the IR bands were much weak, whereas CO adsorbed on film produced an IR absorption band near 1906 cm−1, and an anomalous IR absorption band whose direction has been completely inverted around 1956 cm−1. The direction inversion of the IR band of CO bonded to asymmetric bridge sites on was ascribed to the interaction between Pd nanoparticles inside the aggregates. Based on FTIR spectroscopic and cyclic voltammetric results, the aggregation mechanism of Pd nanoparticles from to has been suggested that the agglomeration of Pd nanoparticles was driven by the alteration of electric field across electrode-electrolyte interface, when the PVP stabilizer was stripped via oxidation during cyclic voltammetry.  相似文献   

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Interfacial area concentration of bubbly flow systems   总被引:2,自引:0,他引:2  
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Desorption of oxygen and hydrogen from various liquids (water, 0.8 molar sodium sulphate solution) containing suspended particles of activated carbon at various solid loading was investigated. The desorption was used to avoid supersaturation effect which was observed during oxygen and hydrogen absorption into liquid saturated with nitrogen. Experiments were carried out in a stirred cell with flat gas-liquid interface at and atmospheric pressure. An increase of kL upon addition of the particles was observed. Enhancement factor increases with increasing contact time of the particles with liquid reaching maximum steady-state value of approx. 3 after sufficiently long time (a few hours) regardless of solid loading , agitator frequency and solute gas (O2,H2). The results fit the correlation (e is specific power dissipated by agitator in liquid and D is molecular diffusivity of gas absorbed) with the exponent for liquids without and for the liquids with the particles. It indicates that the interface is rigid in absence of particles and hinders the motion of liquid along the interface forming boundary layer while in the presence of particles the interface is completely mobile and surface renewal proceeds according to the penetration model. These results confirm a finding of Kaya and Schumpe (2005) that the enhancement of mass transfer in the cell at the presence of hydrophobic solids is due to clean-up of the interface from surfactants by their adsorption on hydrophobic solids rather than by a “shuttle mechanism” exerted by particles with a high adsorption capacity for the transfer component.  相似文献   

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《Polymer》2005,46(25):11322-11329
Poly(3-mesityl-2-hydroxypropyl methacrylate-co-N-vinyl-2-pyrrolidone) P(MHPMA-co-VP) was synthesized in 1, 4-dioxane solution using benzoyl peroxide (BPO) as initiator at 60 °C. The copolymer was characterized by 1H 13C NMR, FT-IR, DSC, TGA, size exclusion chromatography analysis (SEC) and elemental analysis techniques. According to SEC, the number-average molecular weight (Mn), weight-average molecular weight (Mw) and polydispersity index (PDI) values of PMHPMA-co-VP were found to be 58,000, 481,000 g/mol and 8.26, respectively. According to TGA, carbonaceous residue value of PMHPMA-co-VP was found to be 6% at 500 °C. Also, some thermodynamic properties of PMHPMA-co-VP such as the adsorption enthalpy, ΔHa, molar evaporation enthalpy, ΔHv, the sorption enthalpy, , sorption free energy, , sorption entropy, , the partial molar free energy, , the partial molar heat of mixing, , at infinite dilution was determined for the interactions of PMHPMA-co-VP with selected alcohols and alkanes by inverse gas chromatography (IGC) method in the temperature range of 323-463 K. According to the specific retention volumes, , the weight fraction activity coefficients of solute probes at infinite dilution, , and Flory-Huggins interaction parameters, between PMHPMA-co-VP-solvents were determined in 413-453 K. According to and , selected alcohols and alkanes were found to be non-solvent for PMHPMA-co-VP at 413-453 K. The glass transition temperature, Tg, of the PMHPMA-co-VP found to be 370 and 363 K, respectively, by IGC and DSC techniques, respectively.  相似文献   

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