Numerical simulation of bubble dynamics in bubble columns with internals is investigated, and the results show that internal solid walls significantly affect bubble behavior. The trajectories of the selected diameter bubbles tend to be rectilinear, and there are rocking and oscillation for small bubbles which are associated with vortex shedding in the bubble wake. Bubble axially elongates and bubble aspect ratio increases with the increase of internals covered cross-sectional area (CSA). Simultaneously, bubble rise velocity is reduced, and it is related with internals covered CSA and pitch type. Moreover, simulation of bubble dynamics in different diameter internals indicates that hydraulic diameter is the key parameter for scale-up of bubble columns with internals. In addition, bubble breakup and turbulence structure are profoundly impacted by the internal solid walls.

A bubble–emulsion two-fluid model is proposed for the simulation of gas–solid flow in bubbling fluidized beds. This work proposes an analogous research program, according to the analogies in the flow regime and the mechanism between a gas–solid bubbling fluidized bed and a gas–liquid bubble column. The research includes a complete description of the constitutive relationship for interphase forces around the bubbles, a comprehensive investigation of correlations for bubble and emulsion phase properties, and an in-depth analysis of the mechanism of radial nonuniformity in a fluidized bed. The model is verified through comparison of simulated results with experimental data of both Geldart A and B particles. The model is conducted on a coarse grid which shows more potential for the simulation of commercial fluidized equipment.

The solubility of isophthalic acid in propyl acetate and the partition coefficient between propyl acetate and water were measured in the temperature range from (303.2 to 363.2) K. The effect of composition on the partition coefficient was also investigated. The results showed that the changes of the initial concentration of isophthalic acid in the mixtures had a remarkable effect on the partition coefficient. The experimental solubility data were fitted by a logarithmic formula, and the experimental partition coefficient data were correlated with the NRTL activity coefficient model. The calculated results showed good agreement with the experimental data.

A dual-scale turbulence model is applied to simulate cocurrent upward gas–liquid bubbly flows and validated with available experimental data. In the model, liquid phase turbulence is split into shear-induced and bubble-induced turbulence. Single-phase standard k-ε model is used to compute shear-induced turbulence and another transport equation is added to model bubble-induced turbulence. In the latter transport equation, energy loss due to interface drag is the production term, and the characteristic length of bubble-induced turbulence, simply the bubble diameter in this work, is introduced to model the dissipation term. The simulated results agree well with experimental data of the test cases and it is demonstrated that the proposed dual-scale turbulence model outperforms other models. Analysis of the predicted turbulence shows that the main part of turbulent kinetic energy is the bubble-induced one while the shear-induced turbulent viscosity predominates within turbulent viscosity, especially at the pipe center. The underlying reason is the apparently different scales for the two kinds of turbulence production mechanisms: the shear-induced turbulence is on the scale of the whole pipe while the bubble-induced turbulence is on the scale of bubble diameter. Therefore, the model reflects the multi-scale phenomenon involved in gas–liquid bubbly flows.Dual-scale turbulence generation mechanisms involved in gas–liquid bubbly flows: large-scale shear-induced and small-scale bubble-induced.Download full-size image

Experiments and simulations were conducted for bubble columns with diameter of 0.2 m (180 mm i.d.), 0.5 m (476 mm i.d.) and 0.8 m (760 mm i.d.) at high superficial gas velocities (0.12–0.62 m·s− 1) and high solid concentrations (0–30 vol%). Radial profiles of time-averaged gas holdup, axial liquid velocity, and turbulent kinetic energy were measured by using in-house developed conductivity probes and Pavlov tubes. Effects of column diameter, superficial gas velocity, and solid concentration were investigated in a wide range of operating conditions. Experimental results indicated that the average gas holdup remarkably increases with superficial gas velocity, and the radial profiles of investigated flow properties become steeper at high superficial gas velocities. The axial liquid velocities significantly increase with the growth of the column size, whereas the gas holdup was slightly affected. The presence of solid in bubble columns would inhibit the breakage of bubbles, which results in an increase in bubble rise velocity and a decrease in gas holdup, but time-averaged axial liquid velocities remain almost the same as that of the hollow column. Furthermore, a 2-D axisymmetric k–ε model was used to simulate heterogeneous bubbly flow using commercial code FLUENT 6.2. The lateral lift force and the turbulent diffusion force were introduced for the determination of gas holdup profiles and the effects of solid concentration were considered as the variation of average bubble diameter in the model. Results predicted by the CFD simulation showed good agreement with experimental data.