For three types of self-sucking impellers (four-and six-pipe and disk impellers) mixing power, initial point, amount of gas leaving the impeller and mass transfer coefficient were determined experimentally. Investigations were performed for two systems: water and biomass solution.
From the point of view of a minimum mixing power and maximum mass transfer coefficient the best impeller has been chosen. Fuzzy multiobjective optimization for determination of optimum operating conditions is proposed.
List of symbols
c concentration of oxygen D tank diameter d impeller diameter g acceleration of gravity H height of liquid in the tank H' height of liquid above impeller, H' =H-y k consistency Coefficient k L a volumetric mass transfer coefficient N rotational speed of impeller n flow behaviour index P mixing power for pure liquid PG mixing power for aerated liquid V~ volumetric air flow rate y distance of impeller from the tank bottom v. apparent kinematic viscosity of liquid density of liquid time q~ gas hold-up t, P~ Eu-N3 d5 ~ or Eu~ = N3 d5 0 N 2 d Fr= g N 2 d 2
Fr* = o(~-y) vo K 6 -N d 3 N d 2 Re= V a kga Sh = (f/--~a)l/3 Euler Number for non-gassed or aerated liquid Froude Number modified Froude Number gas flow number Reynolds Number Sherwood Number