Laser levitation of solid particles for combustion and gasification applications.

摘要

This dissertation details theoretical and experimental work in the development of a novel combustion diagnostic: laser levitation of solid particles. Theoretical analyses of the forces involved in the suspension of solid particles in a laser beam provide a comprehensive description of the levitation mechanism. Experimental work provides extensive observations and data that describe each of the forces involved, including results from detailed models. Theoretical models establish that a free-convective drag force, light scattering, photon momentum, and other minor forces contribute to the trapping mechanism. The theory quantitatively predicts particle temperature and magnitudes of each of the forces involved. Experimental measurements contain significant scatter, primarily due to the difficulty of making measurements on these very small particles. However, the best estimate trends of the measurements agree well with the predicted behavior despite the scatter. Computational fluid dynamics (CFD) predictions of the free-convective drag force qualitatively agree with published experimental values.;Several different trapping techniques provide single-particle data in literature, including optical tweezers and electrodynamic levitation. However, optical levitation of opaque particles is a relatively new technique and, although less-well understood, provides a potentially powerful novel diagnostic technique for single-particle combustion investigations. The diagnostic consists of a solid-state laser, a high-speed color camera, an infrared camera, and a variety of optics. All experimental data are obtained optically, including particle dynamics, size and shape, and particle temperature. Thus, this technique enables the in situ investigation of micron-sized, solid particles under conditions similar to commercial combustion and gasification processes.;The technique represents a tool for studying combustion and gasification of single, micron-sized, solid particles. Biomass fuels and coal (among many others) provide experimental demonstration of particle suspension. The system suspends particles near the focal point of a visible-light laser, allowing continuous monitoring of their size, shape, temperature, and possibly mass. The Particle Levitation Model (PLM) establishes the trapping mechanism using data from three submodels: an energy balance, a drag force model, and a photon force model. Biomass fuels provide experimental demonstrations of particle levitation under a variety of conditions that illustrate each of the primary levitation mechanisms.