This work presents a combination of Computational Fluid Dynamics (CFD) and Adaptive Network-based Fuzzy Inference System (ANFIS) developed for flow characterization inside a cylindrical bubble column reactor. An attempt has been made to predict the liquid flow pattern and gas dynamics for various ring sparger diameters (i.e., 0.07–0.16 m) and bubble column heights. Gas hold-up, Turbulent Kinetic Energy (TKE) and axial liquid velocity are the output parameters predicted by using the ANFIS method with respect to sparger diameter, axial coordination and radial coordination. Various architectures of the ANFIS method were constructed in order to achieve an accurate prediction model of the liquid flow behavior and gas dynamics inside the bubble column. ANFIS approaches were trained and tested by using CFD simulation results. The performance of the ANFIS approaches was examined by comparing the root mean square error and correlation coefficient values of the prediction models. The CFD simulation results are validated with existing experimental and numerical data and mathematical correlations. Both CFD simulation and ANFIS prediction results show that ring sparger diameter significantly changes the liquid flow pattern and gas dynamics, resulting in different amounts of the gas inside the column. Different ANFIS structures were selected for precise estimation of gas hold-up, TKE and axial liquid velocity. Eventually, the mathematical correlations of the proposed ANFIS approaches are presented with correlation coefficients of 0.9717, 0.9917 and 0.9877 for gas hold-up, turbulent kinetic energy and axial liquid velocity prediction models. Hence, the ANFIS approach is able to provide a prediction of the 3D bubble column hydrodynamics in a continuous domain.

The motion and interaction of a bubble pair in a non-Newtonian fluid (xanthan gum solution) were numerically simulated using a volume of fluid (VOF) method, in which the continuous surface tension model and the power-law model were adopted to represent the surface tension and rheological properties of non-Newtonian fluids, respectively. The effects of the initial horizontal bubble interval, oblique alignment and rheological properties of non-Newtonian fluids on a pair of bubbles rising side-by-side are evaluated in this study. The results indicate that for the case with a non-dimensional initial horizontal bubble interval h* = 4.0, the interaction between the bubbles shows a minimal repulsive effect. Moreover, for the oblique angle alignment a greater repulsive force between the bubbles was seen when the angle was reduced. However, oblique coalescence occurred due to the higher attraction between the bubbles at higher angles, which is independent of the flow index. It is also found that the repulsion effect as well as the variation of the bubble shape from spherical to irregular are more significant at a lower flow index (n < 0.5) due to the shear-thinning effect as well as the differences in their flow field structures.

This paper employs the volume of fluid (VOF) method to numerically investigate the effect of the width, height, and contact angles on burst frequencies of super hydrophilic and hydrophilic capillary valves in centrifugal microfluidic systems. Existing experimental results in the literature have been used to validate the implementation of the numerical method. The performance of capillary valves in the rectangular and the circular microfluidic structures on super hydrophilic centrifugal microfluidic platforms is studied. The numerical results are also compared with the existing theoretical models and the differences are discussed. Our experimental and computed results show a minimum burst frequency occurring at square capillaries and this result is useful for designing and developing more sophisticated networks of capillary valves. It also predicts that in super hydrophilic microfluidics, the fluid leaks consistently from the capillary valve at low pressures which can disrupt the biomedical procedures in centrifugal microfluidic platforms.