الفهرس 
CHAPTER 1: INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Numerical and experimental investigations of swirling and non-swirling (axial) vertical pneumatic conveying dryer are performed. In the numerical study, the Eulerian-Lagrangian model is used to simulate the two-phases. The gas phase is simulated based on Reynolds Averaged Navier-Stokes equations (RANS) employing four turbulence models, namely: standard k-ε model, RNG-based k-ε model, extended k-ε model and low-Reynolds number k-ε model. Meanwhile 3-dimensional particle tracking procedure is used for the solid phase. The pressure-velocity coupling is performed according to the SIMPLE algorithm which is extended to compressible flow.
The model takes into account the lift and drag forces and the effect of particle rotation as well as the particles dispersion by turbulence effect. The solid particles dispersion by turbulence flow is simulated by Stochastic Separated Flow model (SSF)
and the wall roughness is simulated by the virtual wall model. The effects of interparticles collisions and turbulence modulation by the solid particles, i.e. four-way coupling, are also included in the model. An anisotropic model is used to calculate the Reynolds stresses and the turbulent Prandtl number is calculated as a function of the turbulent viscosity. Two approaches for turbulence modulation are tested in the present study. The first one is based on volume and temporal double averaging while the second is based on volume averaging only. The experimental study is carried out on a pilot scale vertical pneumatic transport system. The swirl is imparted to the flow by axially rotating pipe of the same diameter as the drying pipe. Crushed limestone of different sizes is used to represent the solid phase. Measurements of pressure and
temperature distributions along the dryer are performed at different inlet conditions. In addition, several extraction probes are installed along the conveying duct to collect solid samples for solid temperature and water content measurements. The experiments are carried out for pneumatic transport with heat transfer only (inert particles) and for pneumatic drying. The pneumatic transport tests are performed for three thermal conditions namely: isothermal (both phases are introduced at the same temperature), cooling (hot particles are introduced in cold gas stream) and heating (cold particles are introduced in a hot gas stream). Comparisons between present model predictions and available experimental results from literature as well as the experimental data obtained in the present study show good agreement. It is found that the turbulence modulation models that are based on volume averaging only seem to perform better than those based on volume and temporal double averaging. Furthermore, the incompressible ideal gas flow model is found to fairly simulate the heat and mass transfer processes at low flow speeds, while for high speed cases (when the pressure DROP is high), the employment of full compressible flow model is found necessary. For the cases that include swirl flow, the RNG-based k-ε model gives better results than other tested turbulence models. It is also found that introducing cold particles in a hot gas stream (heating) causes pressure DROP reduction in the dilute phase of pneumatic conveying and, on the contrary, the pressure increases in the dense phase. On the other hand, introducing hot particles in a cold gas stream (cooling) causes opposite effects. The boundary layer thickness is found to decreases as the solid mass loading ratio increases. In addition, the drying process is enhanced with increase of both Reynolds number and inlet gas temperature and with the decrease of both particle size and solid
mass flow rate. The drying process is improved due to presence of swirl motion.