4.3 Results and Discussion
111
and rheology provide a tougher falsification test than those currently employed in the
literate, examining if the numerical model is capturing the correct phase-coupling
dynamics in this context.
4.4 Conclusions
This chapter demonstrates that a Eulerian-Lagrangian approach is capable of reproducing the physics underlying structured flows in quasi-2D, pulsed, bubbling, gassolid fluidised beds. Comparative study of simulations using two different approaches
point out the critical role of the coupling between the gas and the solid phase in
sustaining the patterned state. The periodic shift of bubble nucleation sites is induced
by the spatiotemporal variation in solid stress, especially the friction stress, arising
from a dynamic alternation of solid collective behavior between solid-like and fluidlike. The deficiencies of the continuous, Eulerian-Eulerian approach in describing
dense frictional flows confront us with significant challenges to simulate the structured flows witnessed experimentally. Therefore, properly accounting for the granular
rheology of dense flow is critical to recreate the correct appearance of the structured
bubble patterns.
The different dynamics created using these two modelling approaches also highlight the potential of implementing structured flows as an excellent benchmark for
model validation. A robust model for the granular phase should predict the features
properly in the viscous and the plastic regimes, respectively, but also integrate both
kinetic and frictional contributions over the transition regime. This work demonstrates a link between the effects of friction in mesoscopic granular dynamics and
a macroscopic phenomenon in fluidisation by using microscale models to account
for the particle level dynamics. These simulation results serve as a reliable, quantitative base for future developments of models targeting applications on a macroscopic
level.
References
1. Allen MP, Tildesley DJ (1989) Computer simulation of liquids. Oxford University Press, Oxford
2. Anderson TB, Jackson R (1967) Fluid mechanical description of fluidized beds. Equations of
motion. Ind Eng Chem Fundam 6(4):527–539
3. Boemer A, Qi H, Renz U (1997) Eulerian simulation of bubble formation at a jet in a twodimensional fluidized bed. Int J Multiphase Flow 23(5):927–944
4. Bokkers G, van Sint Annaland M, Kuipers JAM (2004) Mixing and segregation in a bidisperse
gas–solid fluidised bed: a numerical and experimental study. Powder Technol 140(3):176–186
5. Boyce CM, Rice NP, Ozel A, Davidson JF, Sederman AJ, Gladden LF, Sundaresan S, Dennis JS,
Holland DJ (2016) Magnetic resonance characterization of coupled gas and particle dynamics
in a bubbling fluidized bed. Phys Rev Fluids 1(7):074201
111
and rheology provide a tougher falsification test than those currently employed in the
literate, examining if the numerical model is capturing the correct phase-coupling
dynamics in this context.
4.4 Conclusions
This chapter demonstrates that a Eulerian-Lagrangian approach is capable of reproducing the physics underlying structured flows in quasi-2D, pulsed, bubbling, gassolid fluidised beds. Comparative study of simulations using two different approaches
point out the critical role of the coupling between the gas and the solid phase in
sustaining the patterned state. The periodic shift of bubble nucleation sites is induced
by the spatiotemporal variation in solid stress, especially the friction stress, arising
from a dynamic alternation of solid collective behavior between solid-like and fluidlike. The deficiencies of the continuous, Eulerian-Eulerian approach in describing
dense frictional flows confront us with significant challenges to simulate the structured flows witnessed experimentally. Therefore, properly accounting for the granular
rheology of dense flow is critical to recreate the correct appearance of the structured
bubble patterns.
The different dynamics created using these two modelling approaches also highlight the potential of implementing structured flows as an excellent benchmark for
model validation. A robust model for the granular phase should predict the features
properly in the viscous and the plastic regimes, respectively, but also integrate both
kinetic and frictional contributions over the transition regime. This work demonstrates a link between the effects of friction in mesoscopic granular dynamics and
a macroscopic phenomenon in fluidisation by using microscale models to account
for the particle level dynamics. These simulation results serve as a reliable, quantitative base for future developments of models targeting applications on a macroscopic
level.
References
1. Allen MP, Tildesley DJ (1989) Computer simulation of liquids. Oxford University Press, Oxford
2. Anderson TB, Jackson R (1967) Fluid mechanical description of fluidized beds. Equations of
motion. Ind Eng Chem Fundam 6(4):527–539
3. Boemer A, Qi H, Renz U (1997) Eulerian simulation of bubble formation at a jet in a twodimensional fluidized bed. Int J Multiphase Flow 23(5):927–944
4. Bokkers G, van Sint Annaland M, Kuipers JAM (2004) Mixing and segregation in a bidisperse
gas–solid fluidised bed: a numerical and experimental study. Powder Technol 140(3):176–186
5. Boyce CM, Rice NP, Ozel A, Davidson JF, Sederman AJ, Gladden LF, Sundaresan S, Dennis JS,
Holland DJ (2016) Magnetic resonance characterization of coupled gas and particle dynamics
in a bubbling fluidized bed. Phys Rev Fluids 1(7):074201