Dispersion in aerosol flow devices

Dispersion in aerosol flow devices

Abstracts DISPERSION 1021 IN AEROSOL FLOW DEVICES Michael Shapiro Faculty of Mechanical Engineering, Technion-Israel Institute of Technology...

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Abstracts

DISPERSION

1021

IN AEROSOL

FLOW DEVICES

Michael Shapiro Faculty

of Mechanical

Engineering,

Technion-Israel

Institute

of Technology,

Haifa 32000, Israel

Principles of aerosol transport mechanics are widely used to model the performance of various aerosol flow devices and to predict their main parameters of engineering interest. These include aspiration and sampling efficiencies and losses in sampling tubes, collection efficiency of fibrous, or granular filters, electrostatic precipitators, etc. Efficient modeling of the aerosol transport and deposition processes is possible in very few cases, pertaining to overly simplistic approximations of the flow field within the device and its geometry. This necessitates development of simplifying approaches, capable of providing a means for sufficiently accurate prediction of basic parameters, while adequately accounting for the device’s geometry and operating conditions. The lecture is devoted to a general description of such an approach, which is applicable to a variety of physical processes and aerosol flow devices. Aerosol particles after entering a flow device achieve an asymptotic spatial distribution within a characteristic (bounded) region, dependent on the geometry of each specific device. This region is the cross-sectional area of a sampling tube, aerosol reactor, or electrostatic precipitator, etc. This process of achieving this asymptotic state is characterized by a balance (within the characteristics region) between the particles’ flux components due to diffusion, convection, and external forces, as well as due to aerosol transformations. This process is called convective dispersion phenomenon. A general theory of such phenomena is aimed to develop a macroscopic description of the above processes, i.e., establish the principles of transport and evolution of an averaged aerosol concentration. Several examples are considered, where this theory is applied to aerosol transport in electrostatic precipitators, porous filters and sampling tubes.

NONSPHERICAL PARTICLES IN A SHEAR FLOW NEAR A SOLID WALL E. Gavze* and M. Shapiro’ * Israel

Institute +Faculty

for Biological of Mechanical

Research, P.O. Box 19, Ness Ziona 74100, Israel Engineering, Technion, Haifa 32000, Israel

Hydrodynamic forces and velocities of nonspherical particles in a simple shear flow near a solid wall are calculated by the Boundary Integral Equation method. The computational results agree with previous studies of Jeffrey, Hsu and Ganatos, and Goldman. Simple correlations are proposed for the lift and the drag forces acting on a stationary ellipsoid near a wall. In contrast with the case of unbounded shear flow, the effect of the wall is to create a velocity component normal to the wall which depends on the distance from the wall and on the particle’s orientation. Inertialess particles at a fixed location near a solid wall perform periodic motion, as their counterparts in an unbounded shear flow, albeit with larger periods. The results obtained for forces acting on prolate spheroidal particles are used to calculate their trajectories in a shear flow.

THE INVESTIGATION OF MAIN PROBLEMS CONNECTED WITH TERRESTRIAL MICROWAVE PROPAGATION IN THE GROUND LAYER OF DESERT ATMOSPHERE UNDER HIGH HUMIDITY CONDITIONS N. Yackerson Department

of Electrical

and Computer

Engineering,

Ben-Gurion

University

of the Negev, Beer-Sheva,

Israel

The process of radiowave propagation is known to be affected by atmospheric content and state. Unlike many other investigations which deal with the influence of ice, rain and snow on signal fading, only limited data about the influence of desert atmosphere are available. The goal of our research is to define the different aspects of the main sources of signal fading, depolarization and distortions in terrestrial links in semiarid areas. Under discussion are the meteorological and climatic peculiarities and the aerosol state of the atmospheric ground layer of the Negev in the equinoctial months and the probable correlation between them and signal distortions. Close to sunset, the Northern Negev atmospheric content is characterized by the specific combination