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The bubble swarm behavior in a system comparable to a flat sheet membrane module was investigated. The parameters channel depth, superficial gas velocity, superimposed liquid velocity and viscosity of the continuous phase were varied. Besides water as continuous phase, a non-Newtonian liquid was used with respect to the rheology of real waste water sludge. The gas hold-up was determined for 144 parameter combinations with high speed imaging and the shear stress – important for the fouling mitigation – was determined for 72 parameter combinations with the electrodiffusion method. To the authors׳ knowledge, this is the first application of the electrodiffusion method in a bubbly flow with a non-Newtonian liquid. For the two properties gas hold-up and the shear stress describing correlations were found taking all parameters into account. In both cases, the strongest influences were found for the gas velocity and the rheology of the continuous phase. Regarding the shear stresses, the median values were up to 3.2 Pa while the maximum values were up to 9.1 Pa. Depending on the parameter combination, a significant influence of the rheology was found disagreeing with the statement of the transferability of the results gained in water to real waste water systems mentioned in some papers. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a novel method to quantify the synergy of bubble swarm patterns and heat transfer performance in a direct-contact heat exchanger (DCHE) by using computational homology. Betti numbers are used to estimate the number of bubbles aggregating in flow patterns and to obtain the pseudo-homogeneous time. A simple linear model of a bubble swarm and the heat transfer performance of a DCHE is constructed on the basis of experimental analysis, in which a new index ( ) is defined by the Betti number average as well as the pseudo-homogeneous time. A good fitting curve between and the volumetric heat transfer coefficient average is obtained with a correlation coefficient of 0.95. A paradigm is established on the basis of this novel method for the study of flow patterns and heat transfer performance, and it offers an alternative route to explore the relationship of flow patterns and heat transfer in other heat transfer processes such as convection, multiphase flow, and turbulent flow. [Copyright &y& Elsevier]

Abstract: A systematic computational study of the dynamics of gas bubbles rising in a viscous liquid is presented. Two-dimensional simulations are carried out. Both the dynamics of single bubbles and small groups of bubbles (bubble swarms) are considered. This is a continuation of our previous studies on the two-bubble coalescence and vortex shedding [A. Smolianski, H. Haario, P. Luukka, Vortex shedding behind a rising bubble and two-bubble coalescence: a numerical approach, Appl. Math. Model. 29 (2005) 615–632]. The proposed numerical method allows us to simulate a wide range of flow regimes, accurately capturing the shape of the deforming interface of the bubble and the surface tension effect, while maintaining the mass conservation. The computed time-evolution of bubble’s position and rise velocity shows a good agreement with the available experimental data. At the same time, the results on the dynamics of bubble interface area, which are, up to our knowledge, presented for the first time, show how much the overall mass transfer would be affected by the interface deformation in the case of the bubble dissolution. Another set of experiments that are of interest for chemical engineers modelling bubbly flows concerns the bubble swarms and their behavior in different bubble-shape regimes. The ellipsoidal and spherical shape regimes are considered to represent, respectively, the coalescing and non-coalescing bubble swarms. The average rise velocities of the bubble swarms are computed and analyzed for both regimes. [Copyright &y& Elsevier]

Removing inclusions from the melt is an important task in metallurgy with critical impact on the quality of the final alloy. Processes employed with this purpose, such as flotation, crucially depend on the particle size. For small inclusions, the aggregation kinetics constitute the bottleneck and, hence, determine the efficiency of the entire process. If particles smaller than all flow scales are considered, the flow can locally be replaced by a plane shear flow. In this contribution, particle interactions in plane shear flow are investigated, computing the fully resolved hydrodynamics at finite Reynolds numbers, using a lattice Boltzmann method with an immersed boundary method. Investigations with various initial conditions, several shear values and several inclusion sizes are conducted to determine collision efficiencies. It is observed that although finite Reynolds hydrodynamics play a significant role in particle collision, statistical collision efficiency barely depends on the Reynolds number. Indeed, the particle size ratio is found to be the prevalent parameter. In a second step, modeled collision dynamics are applied to particles tracked in a fully resolved bubbly flow, and collision frequencies at larger flow scale are derived. [ABSTRACT FROM AUTHOR]

The bubble swarm trajectory in the jet bubbling reactor is measured through the bubble image velocimetry (BIV) technique. The result shows that the bubble swarm rises straightly when the jet Reynolds number is lower than 7,000. However, when the jet Reynolds number exceeds 14,000, the bubble swarm exhibits vortex‐like motion, and the bubble vortices oscillate periodically. The oscillating frequency of bubble vortices under the gas bubbling condition is lower than the flapping frequency of pure liquid jet. Moreover, the moving region and oscillating frequency of bubble vortices increase with the jet Reynolds number. The superficial gas velocity has little effect on the bubble swarm trajectory and the oscillating frequency. An empirical correlation between the oscillating frequency of bubble vortices and the jet Reynolds number is built based on the simple harmonic vibration theory. [ABSTRACT FROM AUTHOR]