Papers by Dimitri Gidaspow
[1] A multiparticle thermofluid dynamic model was developed to assess the effect of a range of pa... more [1] A multiparticle thermofluid dynamic model was developed to assess the effect of a range of particle size on the transient two-dimensional behavior of collapsing columns and associated pyroclastic flows. The model accounts for full mechanical and thermal nonequilibrium conditions between a continuous gas phase and N solid particulate phases, each characterized by specific physical parameters and properties. The dynamics of the process were simulated by adopting a large eddy simulation approach able to resolve the large-scale features of the flow and by parametrizing the subgrid gas turbulence. Viscous and interphase effects were expressed in terms of Newtonian stress tensors and gas-particle and particle-particle coefficients, respectively. Numerical simulations were carried out by using different grain-size distributions of the mixture at the vent, constitutive equations, and numerical resolutions. Dispersal dynamics describe the formation of the vertical jet, the column collapse and the building of the pyroclastic fountain, the generation of radially spreading pyroclastic flows, and the development of thermal convective instabilities from the fountain and the flow. The results highlight the importance of the multiparticle formulation of the model and describe several mechanical and thermal nonequilibrium effects. Finer particles tend to follow the hot ascending gas, mainly in the phoenix column and, secondarily, in the convective plume above the fountain. Coarser particles tend to segregate mainly along the ground both in the proximal area close to the crater rim because of the recycling of material from the fountain and in the distal area, because of the loss of radial momentum. As a result, pyroclastic flows were described as formed by a dilute fine-rich suspension current overlying a dense underflow rich in coarse particles from the proximal region of the flow. Nonequilibrium effects between particles of different sizes appear to be controlled by particle-particle collisions in the basal layer of the flow, whereas particle dispersal in the suspension current and ascending plumes is determined by the gas-particle drag. Simulations performed with a different grain-size distribution at the vent indicate that a fine-grained mixture produces a thicker and more mobile current, a larger runout distance, and a greater elutriated mass than the coarse-grained mixture.
Chemical Engineering Science, Aug 1, 2003
A new computational uid-dynamic (CFD) model with a separate granular temperature (2/3 random part... more A new computational uid-dynamic (CFD) model with a separate granular temperature (2/3 random particle kinetic energy per unit of mass) equation for each phase or particle size was developed using constitutive equations derived earlier by Huilin, Gidaspow and Manger. In agreement with the experiment and model of Mathiesen, Solberg and Hjertager the new model computes the observed core-annular ow regime. It predicts the trends of the observed radial and axial particle diameter distributions. For elastic particles the computed particle velocity distributions are parabolic. They are close to the laminar type approximate analytical solution for ow in a pipe, where the mean velocity equals the inlet ux divided by the particle density and volume fraction. The computed turbulent intensity is lower for large particles than for small particles, as measured. This is in agreement with an approximate analytical solution for the granular temperature in the developed ow region of a riser for elastic particles. Computations show that for suciently inelastic particles the granular temperature in the center can be lower than near the wall resembling the measured particle uctuating velocity distribution. ?
Industrial & Engineering Chemistry Fundamentals, 1983
Time-averaged porosity profiles were measured in a two-dimensional bed with a circular jet and wi... more Time-averaged porosity profiles were measured in a two-dimensional bed with a circular jet and with a rectangular jet by use of a y-ray densitometer. A reglon of maximum porosity was found to exist at a finite length above the jet inlet in the case of the circular jet. This maximum moved up the bed with increasing jet velocity. For the rectangular jet the porosity profiles showed a behavior consistent with two-dimensional calculations. For example, near the jet inlet the concentration profiles were close to elliptical. This geometry can be considered as an idealized cross section of a gasifier. A detailed comparison to numerical solutions of hydrodynamic equations of change will be made in part 2. Jet penetrations for both jets were close to each other.
J Electrochem Soc, Aug 1, 1973
ABSTRACT
The overall objective of this investigation is to develop experimentally verified models for circ... more The overall objective of this investigation is to develop experimentally verified models for circulating fluidized bed (CFB) combustors. Spectral analysis of CFB data obtained at Illinois Institute of Technology shows that the frequencies of pressure oscillations are less than 0.1 Hertz and that they increase with solids volume fraction to the usual value of one Hertz obtained in bubbling beds.
Acs Symposium Series, 2007
ABSTRACT
The overall objective of this investigation is to develop experimentally verified models for circ... more The overall objective of this investigation is to develop experimentally verified models for circulating fluidized bed (CFB) combustors. Sorption of S0[sub 2] with calcined limestone was studied in a PYROFLOW type CFB loop at conditions approximating those found in a CFB combustor. Initially the CFB loop contained 150 micron CaO particles of a density of 3.3 g/cm[sup 3] and air at 1143[degrees]K and 3.25 atm. Atzero time, air containing 600 ppm SO[sub 2], was introduced into the riser bottom at 1143[degrees]K. The effect of gas velocity, sorbent inventory and inlet pressure on the sorption of SO[sub 2], were studied isothermally by running our hydrodynamic code with the S0[sub 2] sorption conservation of species equation. At a velocity of 5m/sec., reported to be a typical velocity by PYROPOWER, there is reasonably good S0[sub 2] removal. At 10 m/sec the S0[sub 2] removal is poor. The best SO[sub 2], removal is for a velocity of 5 m/s and a high bed inventory, initial bed height, H = 9m. Most of the S0[sub 2] is removed in the first two meters of the reactor. However, the S0[sub 2] removal is not complete at the bed outlet. This is due to mixing. At the left wall of the reactor (wall opposite the solids inlet) the S0[sub 2] removal was poor due to gas bypassing caused by the asymmetrical solids inlet. Simulation of the PYROPOWER loop with a symmetrical inlet gave us an order of magnitude improvement over the conventional PYROPOWER system. These results demonstrate the practical utility of the predictive model that we have developed over the last three years.
Chemical Engineering Science, Jul 1, 2007
A literature review shows that dispersion coefficients in fluidized beds differ by more than five... more A literature review shows that dispersion coefficients in fluidized beds differ by more than five orders of magnitude. To understand the phenomena, two types of hydrodynamics models that compute turbulent and bubbling behavior were used to estimate radial and axial gas and solid dispersion coefficients. The autocorrelation technique was used to compute the dispersion coefficients from the respective computed turbulent gas and particle velocities.
The design of fuel cell batteries with a stationary electrolyte must include an estimate of the h... more The design of fuel cell batteries with a stationary electrolyte must include an estimate of the highest local temperature which might result. An infinite series solution for the temperature distribution in a battery with a constant rate of heat generation, as well as a partial thermal stability analysis, has already been published by the first two authors. Charts are given
... CURVE ANALYSIS FOR REACTION CONTROLLED ISOTHERMAL SORPTION WITH DIFFUSION INTO SPHERICAL PART... more ... CURVE ANALYSIS FOR REACTION CONTROLLED ISOTHERMAL SORPTION WITH DIFFUSION INTO SPHERICAL PARTICLES DIMITRI GIDASPOW, DILIP DHARIAt and LINUS LEUNG Institute of ... [18] in 1946, Amundson [19] in 1948, Katz [20] in 1953 and Chu and Hauser ...
A cross-cooled solar powered air conditioning system using silica gel is being studied. The syste... more A cross-cooled solar powered air conditioning system using silica gel is being studied. The system consists of two identical fixed bed dehumidifiers. One dehumidifies while the other is being regenerated. Cross-cooling is achieved with air flowing through rectangular channels and the process stream flows in perpendicular channels which are lined with paper-like sheets consisting of micron size silica gel particles held in a Teflon web. A prototype dehumidifier was constructed and tested and the results are compared with computer simulation predictions. A complete cooling system based on optimum COP and minimum pressure drop (for a given size) will be designed, built and tested. Preliminary calculations predict a COP of about 0.50 with 82 C regeneration temperature. Due to the low pressure drop in the channels the electric coefficient of performance (EER) is very high.
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Papers by Dimitri Gidaspow