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Turbulent flow patterns of dilute gas-particles flows in a vertical pipe are numerically investigated according to the Eulerian-Lagrangian approach by using the k ¼ e model. Calibration of the numerical tools (commercial CFD software (FIDAP 8.6) and additional computer programs) is obtained by confirming the numerical predictions with available experimental results. Additionally, a comparison between the present work and experimental data showed an average deviation of about 3% and a maximum deviation of about 6% (for 0.1 mm particle diameter). The effect of geometrical parameters, flow parameters, and materials characteristics on gasparticles flow behavior were studied. It was observed that an increase in particle diameter, loading ratio, Re number (for constant loading ratio and variable mass flow rate), and particle density increased the acceleration length and the slip velocity. For a constant mass flow rate and variable loading ratio, a higher Re number increased slip velocity but decreased acceleration length. Additionally, it was found that variations in pipe diameter have negligible effect on the acceleration length and slip velocity for constant particle mass flow rate and constant loading ratio.

Measurements of the natural convection drag and the photophoretic force have been conducted for Spherocarb char particles as a function of carbon conversion. These forces were obtained by measuring the balancing voltage with and without laser heating during the reaction of single particles in an electrodynamic balance. The photophoretic force was determined by subtraction of the calculated natural convection force, after an initial transient corresponding to.about five percent carbon conversion during which the natural convection force was dominant. The particle conductivity inferred from the photophoretic force was found to increase by more than one order of magnitude as the reaction progressed, qualitatively in agreement with models of the dependence of conductivity on porosity. Confirmation of the temperature gradient across the particle was provided by the development of asphericity in the particles when heated from below but not when heated uniformly. The simultaneous measurements of the mass, diameter, and particle conductivity as a function of Carbon conversion provides a critical test of pore evolution models since the reaction rate is dependent on the accessibility of the internal surface area to the reactant gas through the open pore structure and the thermal conductivity is dependent on the connectivity of the solid structure. Induction periods were observed before the reaction rate accelerated and the particle conductivity declined, confirming the influence of pore structure on both. Particles could be reacted to a high conversion of greater than 95 percent without any evidence of fragmentation providing further insight on the connectivity of the solid surfaces.

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