Tham khảo tài liệu 'mass transfer in chemical engineering processes part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 90 Mass Transfer in Chemical Engineering Processes such that Ugs is the relative velocity between the phases given by Ugs Ug - Us I. In the above equations figs represents the drag force between the phases and is a function of the interphase momentum coefficient Kgs the number of particles in a computational cell Nd and the drag coefficient CD such that figs Kgs Ug - Us I NC 1 Pg Ug - Us I Ug - U Af P4 Cd 1Ps Ug - Us Ug - ũ ĩị 4 CD p- Ug - Us U g - Us 4 The form of the drag coefficient in Equation 4 can be derived based on the nature of the flow field inside the computational domain. Several correlations have been derived in the literature. A well established correlation that takes into consideration changes in the flow characteristics for multiphase systems is Ossen drag model presented in Skuratovsky et al. 2003 as follows 64 2 64 Cd 11 7--I for Re -Kes J Cd -64- 1 10 for Res 7Ĩ Res X Res - Res 5 Cd -4 1 for Re 133 tfRe s ln Cd - Res ln2 Res - ln3 Res for 40 Res 1000 The form of Reynolds number defined in Equation 5 is a function of the gas properties the relative velocity between the phases and the solid phase diameter. It is given by Res P p -U d 6 The virtual-mass force F vm in Equations 2 3 accounts for the force needed to accelerate the fluid surrounding the solid particle. It is given by -- ----- r _ dUg dUs Fvm UsPgCvm 0 dt dt 7 Complimentary equations - granular kinetic theory equations When the number of unknowns exceeds the number of formulated equations for a specific case study complimentary equations are needed for a solution to be possible. For a binary Numerical Simulation of Pneumatic and Cyclonic Dryers Using Computational Fluid Dynamics 91 system adopting the Eulerian formulation such that q g for gas and s for solid the volume fraction balance equation representing both phases in the computational domain can then be given as n t 1 q 1 8 -V where a -q V In the .
