This review presents the development and application of a new approach for studying single particle kinetics that can provide new insights into particulate combustion. The new approach uses the capability of suspending a charged particle motionless at a fixed position in an electrodynamic chamber (EDC). The particle is heated by means of laser radiation. The new approach combines the capabilities of classical thermogravimetric and calorimetric approaches with those of drop tube experiments without some of the accompanied limitations. In this approach the particle can be well characterized prior to reaction. If after the reaction the particle is still suspended it can be further characterized in the chamber then it can be captured and off-line characterization can be carried out. The method is presently capable of providing information prior to, during, and past reaction on the mass, size, density, heat capacity, light absorptivity, porosity, phase transition, reaction enthalpies, thermal and inertial characteristic times, ignition temperatures and ignition delay times. The issues connected with heating with laser radiation include (1) the nature of internal electromagnetic field within the particle, (2) transient heat changes, and (3) photophoretic phenomena. In order to reach the desired temperature by radiation a laser beam has to be focused to a size of the particle diameter. Small movement of the particle may upset the heat balance. It is thus of essential importance to develop methods that will control the particle motionless at the center of the chamber in spite of the changes in the force balance it may experience. A feature of this technique is that the surroundings are at ambient temperature (300 K). The lack of external source (other than laser radiation) permits the steady determination of the heat release rates and the measure of heat capacities. Also, secondary reactions in the boundary layer such as CO oxidation are minimized enabling one to concentrate on the surface reactions. Ignition studies in the presence of controlled external heating can provide new insights into particulate ignition. High relative gas velocities surrounding the particle can be achieved thus simulating reactions under high flow fields. The present approach is however not without its drawbacks. Thermoionic emission can lead to problems of particle stability and the small sample size limits gas analysis to major products. The present review provides a discussion of the capabilities and limitations of the electrodynamic chamber for high temperature applications. The review discusses in detail the methodology of the EDC. Theoretical aspects of the important processes and phenomena in conjunction with the operation of the EDC are provided. The motivation of the detailed theoretical presentation is twofold: (1) To provide the user with tools necessary to estimate the operation conditions of the specific system. (2) To evaluate the force balance from phenomena taking place during the heterogeneous reaction not connected with the reaction and correct the interpretation of the results accordingly.
ASJC Scopus subject areas
- Chemical Engineering (all)
- Fuel Technology
- Energy Engineering and Power Technology