1,721,083 research outputs found
Development of New Methods for the Solution of Inverse Electromagnetic Scattering Problems by Buried Structures – State of the Art and Open Issues
No full text
Which model for inversions? The case of strong scatterers.
No full textWe analyze the performances of a Physical Optics (PO) based shape reconstruction algorithm for the retrieval of strong
metallic scatterers in a subsurface measurement configuration.
For the sake of shape reconstruction and when the impinging field is provided by current filaments, we can regard the PO algorithm
as one of assuming the magnetic field on the illuminated side, after normalization to unessential factors, as linear in phase and
growing with the square root of the frequency in amplitude, as far as the dependence on the frequency is concerned. Therefore, we
numerically analyze, with reference to the case of circular cylindrical strong scatterers, the limits of validity of such a model for
inversion purposes and we validate an inversion algorithm based on the Singular Value Decomposition approach on synthetic data
Characterization of the Devolatilization Rate of Solid Fuels in Fluidized Beds by Time-Resolved Pressure Measurements
No full textThe characterization of volatile matter (VM) release from solid fuel particles during fluidized-bed combustion/gasification is relevant to the assessment of the reactor performance, as devolatilization rate affects in-bed axial fuel segregation and VM distribution across the reactor. An experimental technique for the characterization of the devolatilization rate of solid fuels in fluidized beds is proposed. It is based on the analysis of the time series of pressure measured in a bench-scale fluidized-bed reactor as VM is released from a batch of fuel particles. A remarkable feature of the technique is the possibility to follow fast devolatilization with excellent time-resolution. A mathematical model of the experiment has been developed to determine the time-resolved devolatilization rate, the devolatilization time and the volume-based mean molecular weight of the emitted volatile compounds. Devolatilization kinetics has been characterized for different solid fuels over a broad range of particle sizes. (C) 2011 American Institute of Chemical Engineers AIChE J, 58: 632-645, 201
A NOVEL TECHNIQUE FOR IN-SITU CHARACTERIZATION OF DEVOLATILIZATION RATE OF SOLID FUELS IN FLUIDIZED BEDS.
No full textThe characterization of volatile matter (VM) emission from solid fuel particles during fluidized bed combustion/gasification is relevant to reactor performance influencing the fate of VM as it results from competing phenomena of release, mixing/segregation and burn-out. The rate and the time-history of volatile matter release strongly affect axial segregation of fuel particles in the bed, favoring the establishment of the stratified combustion regime. On the other hand, the comparison between the devolatilization and radial solids mixing time scales affects the radial distribution of volatile matter across the reactor. Short devolatilization times determine VM release localized near feeding point. The knowledge of devolatilization kinetics, as determined by thermogravimetric analysis, does not take into account key process phenomena such as the effective time-temperature history of the devolatilizing particle.A novel and easy-to-use diagnostic technique for “in-situ” characterization of the devolatilization rate of fuel particles in gas fluidized beds is proposed in the present paper. It is based on the time-resolved measurement of pressure in a bench scale fluidized bed reactor equipped with a calibrated flow restriction at the exhaust. The procedure consists of the injection of a single fuel particle (or small batches of multiple particles) and continuous monitoring of the pressure in the reactor. The bed was kept at a constant temperature by external heating and fluidized with nitrogen. Gas pressure inside the reactor increases during devolatilization as a consequence of the increased flow rate, due to the emission of volatile matter, across the calibrated flow restriction at the exhaust.Experimental data are analyzed in the light of a model of the experiment based on the transient mass balance on the reactor volume referred to the fluidizing gas and to the volatile matter. The comparison between experimental pressure time series and model computations enables the characterization of the kinetic parameters of devolatilization rate for samples of different coals as well as of non-fossil solid fuels
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