Three-Dimensional DPM-VOF Numerical Simulations On Bubbling Behavior In Single Orifice Bubble Columns With Low Holdup Of Solid Particles

Three-dimensional (3D) physical and mathematical models were formed bycoupling discrete particle model (DPM) and volume of fluid (VOF) method withcorresponding initial and boundary conditions in this thesis.3D numerical simulationson the bubbling behaviors (including bubble formation, detachment and rising) ofsingle orifice bubble column with the presence of dulite particles（s≤4.19％）wereperformed based on Fluent6.3.In the simulation process, both gas and liquid (Eulerian phases) were modeled witha continuity equation and a single set of momentum equations together; the VOFprocedure was used to track the interface of the bubbles. The Lagrangian particleswere linked to the Eulerian phases with a two-way coupling through interchangeterms in the respective momentum equations. Grid independence was checked byincreasing grid number, part of the computational domain was refined with a localrefining method, and in that case, the calculation amount could be reduced with anaccepted accuracy. At last, a0.5-1mm grid arrangement was selected in this paper. A10mm bubble in diameter rising in liquid-solid suspension was simulated andcompared with literature data, the relative error of this simulation is below7%.Simulations of both gas-liquid and gas-liquid-solid flows are in qualitative agreementwith experiment results.The particle and fluid properties, operating conditions and wettability of orificematerial were investigated numerically. The results show:3D simulation can displaythe spiral path of bubble rising in liquid-solid suspension virtually. Under currentresearch conditions, the presence of particles delays the bubble detachment period,enlarges the bubble size and slows down the bubble rise velocity. tdbecomes a bitlonger with more particles, turns to be delayed globally with larger particle diameter,shows no relationship with particle density; either increasing particle number ordensity leads to larger bubble diameter, dbenlarges globally with particle diameterincreasing; either increasing particle number or density demonstrates reduction effecton bubble rise velocity, but vbfluctuates with particle diameter increasing. A strongwake region appears behind the bubble while it’s rising, the wake region leads to localpressure difference which attracts particles, and then the particle entrainment happens. The wettability of orifice material is of significant effect on the process of bubbleformation. Generally, increasing the contact angle favors the bubble base on orificematerial to spread outwards, which leads to larger bubble size. It is observed that thebubble detachment time decreases with increasing orifice gas velocity or superficialliquid velocity as well as with decreasing liquid surface tension, however, liquidviscosity shows little effect in this regard. Only the liquid surface tensiondemonstrates dramatic effect on bubble size. The bubble rise velocity increases byspeeding up superficial liquid velocity but tends to be slowed down slightly whileincreasing orifice gas velocity or liquid viscosity. Maximum bubble rise velocityhappens while changing liquid surface tension.