This dissertation develops a modeling framework for predicting the behavior of fibrous bulk solids in pneumatic conveyance systems that are currently not possible with conventional computational models. The developed framework allows designers to computationally predict flow characteristics of fibrous bulk solids, which impacts pneumatic conveyance system performance. These performance characteristics include air and fibrous bulk solids velocity profiles, fibrous bulk solids concentrations, pressure loss, and general system behavior. The motivation for this research is to expand the capabilities of computational models within in the engineering design process, rather than relying solely on generalized experimental correlations and previous design experience.

This framework incorporates the primary characteristics of fibrous biomass-based bulk solids including low density, large characteristic length, and non-spherical shape. The main features of the developed modeling framework are (1) the effects of the particle drag on the flowing air and (2) the resistive effects of the interconnected fibers between the particles. The models are implemented within a commercially available CFD solver package with user-defined functions. Velocity profiles, bulk solids concentration, and air pressure are modeled with the differential conservation equations for mass and momentum based on the Eulerian-Eulerian multiphase modeling approach. The inter-particle and the particle-air interactions result in momentum exchanges, and these exchanges are incorporated into the model through a series of externally defined user functions that account for the momentum exchange due to drag of the particles and the resistance of the connected fibers. These user-defined functions allow the user to set a series of parameters specific to the transported bulk solids and to the loading conditions. The model is applied to two specific studies, which include (1) cotton-air flow through a positive pressure pneumatic conveyance system and (2) biomass-air flow through a negative pressure (vacuum) conveyance system. The model parameters are chosen to match existing experimental data obtained from their corresponding lab tests.