Recent studies are sponsored by grant DTK02/46 of the National Science Fund of Bulgaria.
PhD studies of Dr. Georgiev, now lecturer in the National Military School in Veliko Turnovo, North Bulgaria

Aims of project:

  1. Design and study of impellers for energy-saving operation in viscous fluids.
  2. Bioreactor modeling to achieve enhanced bioreaction performance assessed as augmented conversion to exopolysaccharides.

Principle description and illustration. Various impeller designs (Image 1) were examined to improve the mixing bioreactor performance, i.e. to achieve good operation at low input power.

Fluent options engaged: RANS modeling, standard and realizable «k-ε» model, Multiple Reference Frame (MRF) modeling approach, 2-D and 3-D post-processing – iso-surface visualization, report option averaging and histograms, velocity functions and turbulence functions visualization.

ResultsReplacing FB by FFB has allowed:

  1. Larger spread of similar shear deformation rate at low power input, as illustrated in Image 3.
  2. Improving homogenization as illustrated by the 2-D velocity contours and the hystograms in Image 4.

 

Achievements

CFD simulation of impeller performance in bioreactors producing exopolysaccharides has been carried out to study flow performance deterioration at viscosity/consistency rise. Stagnant zones have been uncovered to predict substrate and oxygen depletion. Optimization steps were carried out to neutralize flow field deterioration by variation of mixing intensity and retrofitting of mixer design. The results may be helpful for the reported highly viscous bioprocesses challenged by poor mixing performance and low oxygen mass transfer efficiency.

 

Project CFD assessment of particle wall shear rates in stirred and biofilter fixed bed reactors.

Cooperation with Hungary: with Zs. Csanadi, E. Nagy, and Cs. Sisak from the Research Institute of Chemical and Process Engineering in Veszprem and Cooperation with France with I. Nikov from Lille Polytechnics,Lille.

Aim of project: Evaluation by CFD methodology of near-particle flow conditions in a model particle-based fixed bed bio-film reactor for 2-propanol degradation, in view of diagnosing bio-film stability. Similar analysis in a stirred vessel.

Principle description and illustration: Particles in biofilm reactors are covered by bacterial film threatened by flow erosion. Particle wall shear rates exceeding 10 ks-1 have been reported as critical for biofilm detachment. Thus, shear rates were determined by CFD simulation.