Date of Award

Spring 1999

Document Type

Thesis

Degree Name

Master of Science in Environmental Engineering - (M.S.)

Department

Civil and Environmental Engineering

First Advisor

Mohamed E. Labib

Second Advisor

Taha F. Marhaba

Third Advisor

Robert Pfeffer

Abstract

Disaggregation of dry powders in shear flow has limitations in producing submicron particles. This study explores a new method for the production of submicron particles by the depressurization of powder aerosols. The depressurization mechanism is based on the rapid depressurization of the aggregated powder through a specially designed nozzle. As the pressure suddenly decreases from very high values inside the aggregates (800 psi) to ambient at the surface of such aggregates, disaggregation takes place due to the force exerted by the gas escaping through their pore structure.

he effect of various process parameters, namely: nozzle diameter, pressure and pretreatment with surfactants were investigated. Comparison of the particle size distribution produced indicated that better disaggregation is achieved with the smaller nozzle diameter. The results showed that a pressure of 100 psi was sufficient to effect disaggregation on powder by overcoming the secondary forces within the aggregates. The product particle size distribution showed a weak dependence on pressure upto 800 psi. The enhancement of disaggregation by surfactants pretreatment was not very significant. This novel method is expected to be significant in the production and processing of submicron and nanoparticles.

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