A study of hydrodynamics and interfacial momentum exchange terms in cylindrical bubble column by CFD
Multi-scale and/or multi-disciplinary approach to process-product innovation
CFD & Chemical Engineering- II (T3-4b)
Keywords: bubble column, hydrodynamics, CFD, population balances, bubble coalescence
Flow fields and bubble size distribution are two critical issues in the determination of reaction rate and mass transfer in bubble columns. In this work the hydrodynamics of a laboratory scale cylindrical bubble column full of tap water and with a diameter of 0.19 m and height of 1.7 m were studied. The calculated flow fields obtained by ANSYS CFX 10 were verified by the experimental results gained from PIV measurements.
The Eulerian-Eulerian approach was used as the most reasonable multiphase model in the study. The k-epsilon turbulent model was used for the liquid. For the source term of the Eulerian-Eulerian model in the domain, the coalescence and breakage of bubbles were considered by discretization of the population balance equations using the MUSIG model. In this study, 5 different bubble size groups with the size between 3-8 mm were considered in the MUSIG model. The Prince & Blanch and Luo & Svendsen models were selected as the coalescence and breakage models, respectively.
The interface momentum exchange terms in the Eulerian-Eulerian model were examined by different drag and non-drag force models. In the non drag forces the effect of lift, turbulent dispersion, virtual mass and wall lubrication forces on time averaged liquid, slip and bubble velocity and gas hold up were studied. The validated results by PIV show that the drag, lift and turbulent dispersion forces are the most important momentum transfer terms in the model. However, the effect of the wall lubrication force is also considerable. Slightly more accurate results can be obtained by including the virtual mass force in the calculation. However, the inclusion of virtual mass force causes some convergence problems increasing the computation time remarkably. The study shows that the appropriate drag model has crucial effect on the hydrodynamics of the domain. Moreover, the effect of the bubble size on the lift force should be considered. This behavior can affect the radial gas hold up distribution and also water velocity vectors in the column.
The effect of the inlet gas velocity was examined by solving the same geometry with verified model parameters for different inlet gas velocities. The simulated time averaged liquid, slip and bubble velocity vectors accompanied by turbulent kinetic energy distribution in the column were verified by the PIV results in the same experimental conditions. Also, vertical distributions of the time averaged gas hold up at different inlet gas velocities were compared.
See the full pdf manuscript of the abstract.
Presented Tuesday 18, 16:40 to 17:00, in session CFD & Chemical Engineering- II (T3-4b).
