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Integration of Population Balance Method and Computational Fluid Dynamics for Simulation of Bubble Column Hydrodynamics

Baghaei, Ali | 2009

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 40070 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Bastani, Dariush; Sarrafi, Amir
  7. Abstract:
  8. Different modeling and simulation techniques, new numerical methods and analyzing effects of different parameters on operation of bubble columns are continuously under study for optimized design, scale-up and prediction of industrial bubble columns. Tools for analyzing and developing gas-liquid systems are experimental techniques and computational fluid dynamics (CFD). In order to describe accurately the fluid dynamics of complex gas-liquid systems, more advanced mathematical models are required. To obtain a feasible numerical solution, efficient numerical techniques must be devised. One of such models that considerably reduces the assumptions and consequently increases the accuracy of results is population balance model. As CFD techniques developed, new methods were introduced to increase speed and accuracy of solution to population balance equations (PBE). In the present work, a new technique for solution of PBE in gas-liquid flow inside a bubble column is presented. Three different Eulerian/Eulerian multiphase models, two-fluid and mixture model, were considered with the population balance equation (PBE), accounting for bubble coalescence and breakage, is considered. Although the new method is basically a variant of classes method, but it is comparable with new complicated techniques available in literature. In this method, each time step is divided into two sub-steps, first hydrodynamic equations are solved without any coalescence and breakage phenomena, and then the bubbles are affected by these phenomena. The original bubbles are the divided into three groups of classes which include bubbles form from breakage of other bubbles, bubbles formed by coalescence and non-altered bubbles. The accuracy of the new technique with 20 classes is comparable with classes method with 100 classes. In order to validate the model results, a cubic bubble column was designed and constructed. Bubble size distribution was calculated by photography. The results show that new technique has an acceptable accuracy in prediction of bubble size distribution. A correlation was presented to predict gas hold-up in cubic bubble column. Wile performing experiments, a new phenomenon called “Bubble Bunch” was observed and studied comprehensively. The formation reason of bubble bunch was investigated and decreased surface tension was found to be the main cause.
  9. Keywords:
  10. Multiphase Flow ; Bubble Column ; Computational Fluid Dynamics (CFD) ; Bubble Size ; Population Balance

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