Abstract (Summary)
In many plasma-aided manufacturing systems, metallic or ceramic particles are introduced in a thermal plasma. The heat transfer from the plasma to the particle, in part, governs the quality of the products. To design thermal plasma-aided manufacturing systems and to predict their performance, accurate determination of particle heat transfer is necessary. In this thesis, a spherical particle introduced in an ionized gas made up of electrons, ions, and neutrals is considered. A model to accurately determine heat transfer to the particle is developed. As the temperatures encountered in typical DC plasma systems are very high, the Debye length is less than the mean free path. A continuum approach is not valid under such a condition. Hence a kinetic theory approach is adopted. Maxwell's transport equations are obtained by taking moments of the Boltzmann equation. The transport equations are solved with the Poisson's equation for the self-consistent electric field using two-sided electron and ion velocity distributions. The solutions of the governing equations provide the ion and the electron number density distributions and the electric potential variation. The charged species flux to the particle surface is evaluated. Heat transport to the surface is calculated by accounting for heat conduction and the energy deposited during electron and ion recombination at the surface. Effects of plasma pressure, temperature, composition, and particle size on the particle heat transfer have been examined. In the range of plasma temperature considered here, the particle floating potential is found to vary linearly with plasma temperature and matches very well with available experimental data. At high temperatures, heat transfer coefficient in an ionized gas flow is substantially higher than that in a non-ionized gas. The contribution to heat transfer by charged species recombination at the particle surface increases with plasma temperature. As the operating pressure is increased, the heat transfer due to ionization increases. Results clearly show that under typical conditions in DC plasma systems, the heat transfer to a particle due to recombination of electrons and ions on the particle surface is substantial and must be taken into account to accurately evaluate the net heat transfer. The model developed in this thesis can be used for this purpose.
Bibliographical Information:


School:University of Cincinnati

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:heat transfer plasma spraying kinetic theory ionized gases


Date of Publication:01/01/2001

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