Date of Award

Spring 2005

Document Type

Thesis

Degree Name

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

Department

Mechanical Engineering

First Advisor

Edward L. Dreyzin

Second Advisor

Rajesh N. Dave

Third Advisor

Mirko Schoenitz

Abstract

The thermal processes leading to ignition of metal powders in environments that experience rapid temperature changes are currently poorly understood. In this research, a methodology for studying and quantification of such processes is developed. In the experimental case study, the ignition temperature of Mg powder coated on the surface of an electrically heated filament is detected optically at different heating rates. To interpret the results, a heat transfer model has been developed for a multilayer powder coating on top of an electrically heated filament. The coating is modeled using a hexagonal close packed geometry and the heat transfer equations are derived for one dimensional heat flow. An Arrhenius type expression is used to describe the chemical reaction leading to ignition with the pre-exponent as an adjustable parameter. The contact resistance between each powder layer was derived using the bulk thermal properties of the powder. The thermal diffusivity of the powder was measured using the laser flash diffusivity technique for a powder sample freely loaded in a thin cylindrical cavity made in a heat insulator. The pre-exponent identified by matching the computations with the experimental data is 1 x 1010 kg/m2s. For the Mg powder, it is concluded that the thermal processes leading to ignition, for a range of heating rates between 90 and 16,000 K/s, can be described by a single Arrhenius expression. In general, the developed methodology was validated can now be used for studying ignition of different reactive powders.

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