David Levi-Hevroni

Mathematical Modeling of Drying of Liquid/Solid Slurries in Steady State One-Dimensional Flow

ABSTRACT A mathematical model of simultaneous mass, heat and momentum transfer for two-phase flow of a gas and a solid/liquid slurry was developed. The model was applied to calculation of the drying process of coal-water slurry droplets in a gas medium in a steady one-dimensional flow. The model was based on the well-known two-stage drying process for slurry droplets. After the first period of drying, in which the evaporation rate is controlled by the gas phase resistance, the evaporating liquid diffuses through the porous shell (crust) and then, by convection, into the gas medium. Inside the dry external crust of the drop, a wet central core forms, which shrinks as evaporation proceeds. The temperature of the slurry droplet rises. The process ends when the temperature of the dry outer crust reaches the coal ignition temperature in the case of combustion or when the moisture of the particle reaches the final required moisture. The developed model was based on one-dimensional balance equations of mass, ene...

Numerical investigation of the propagation of planar shock waves in saturated flexible porous materials: development of the computer code and comparison with experimental results

The three-dimensional governing equations of the flow field that is developed when an elasto-plastic exible porous medium, capable of undergoing extremely large deformations, is struck head-on by a shock wave, are developed using a multi-phase approach. The one-dimensional version of these equations is solved numerically using an arbitrary Lagrangian–Eulerian (ALE) based numerical code. The numerical predictions are compared qualitatively to experimental results from various sources and good agreement is obtained. This study complements our earlier study in which we developed and solved, using a total variation diminishing (TVD) based numerical code, the governing equations of the flow field that is developed when an elastic rigid porous medium, capable of undergoing only very small deformations, is struck head-on by a shock wave.

The interaction of planar shock waves with multiphase saturated flexible porous materials – a numerical investigation

The three-dimensional governing macroscopic equations of the flow field which is developed when an elasto-plastic highly deformable open-cell porous medium whose pores are uniformly filled with liquid and gas is struck head-on by a planar shock wave, are developed using a multiphase approach. The one-dimensional version of these equations is solved numerically using an arbitrary Lagrangian Eulerian (ALE) based numerical code. The numerical predictions are compared qualitatively to experimental results from various sources and good agreements are obtained. This study complements our earlier studies in which we solved, using an ALE-based numerical code, the one-dimensional governing equations of the flow field which is developed when an elasto-plastic flexible open-cell porous medium, capable of undergoing extremely large deformations, whose pores are saturated with gas only, is struck head-on by a planar shock wave.

Two-dimensional model for simulating shock-wave interaction with rigid porous materials

A two-dimensional numerical model for predicting the characteristics of the e owe eld during an unsteady interaction between a shock wave moving through air and a rigid saturated porous matrix is developed. The numerical modelincludesa Lagrangianschemecombined with aremeshand an interfacetrackingtechnique.Thepredictions of the numerical simulations are compared with the predictions of a two-dimensional analytical model for regular ree ection from a rigid porous surface in pseudosteady e ow. The numerical and the physical model are also validated by comparing the one- and two-dimensional predictions of the model with experimental results. In general the predictions of the numerical simulations reveal very good to excellent agreement with both the experimental results and the predictions of the analytical model. Nomenclature C® = specie c heat capacities ratio for the ® phase c® = shape factor for the ® phase

Lateral sample motion in the plate-rod impact experiments

Velocity of the lateral motion of cylindrical, 9 mm diameter 20 mm length, samples impacted by WHA impactors of 5-mm thickness was monitored by VISAR at the different points of the sample surface at distance of 1 to 4 mm from the sample impacted edge. The impactors were accelerated in the 25-mm pneumatic gun up to velocities of about 300 m/sec. Integrating the VISAR data recorded at the different surface points after the impact with the same velocity allows to obtain the changes of the sample shape during the initial period of the sample deformation. It was found that the character of the lateral motion is different for samples made of WHA and commercial Titanium alloy Ti-6Al-4V. 2-D numerical simulation of the impact allows to conclude that the work hardening of the alloys is responsible for this difference.

Two-dimensional effects of the head on interaction between planar shock wave with low density foam

Two-dimensional physical and numerical models for predicting the characteristics of the flow field during an unsteady interaction between a planar shock wave moving through air and a deformable saturated porous material were developed using the Representative Elementary Volume (REV) approach. The numerical model is based on a two-phase finite Arbitrary Lagrangian Eulerian (A.L.E) difference scheme for solving the two dimensional version of the governing equations. The numerical predictions are compared qualitatively and quantitatively to experimental results and good agreements are obtained both in one and two dimensional cases.

Head-On Collision of a Planar Shock Wave with Deformable Porous Foams

Two-dimensional physical and numerical models for predicting the characteristics of the flowfield during an unsteady interaction between a planar shock wave moving through air and a deformable saturated porous material were developed using the representative-elementary-volume approach. The numerical model is based on a twophase arbitrary Lagrangian Eulerian finite difference scheme to solve the flowfield governing equations. The multidimensional effects of the head-on collision were investigated. The physical model is validated by comparing the numerical predictions qualitatively and quantitatively to one- and two-dimensional shock-foam interaction experimental results. Good agreement was obtained both in one- and two-dimensional cases. It was found that wall friction results in shear bands (i.e., localized high vorticity), which affects the flowfield characteristics. Therefore, the common one-dimensional models are not valid in the vicinity of the shock tube sidewalls. Nomenclature Cα = specific heat capacities ratio for the α phase cα = shape factor for the α phase