Effectiveness factor in biological external convection:: study in high viscosity systems

A study regarding the influence of mixing on the efficiency of alginate and xanthan synthesis was carried out. The effectiveness of these two systems in terms of a dimensionless reaction convection number (N-RC), which is a function of the power input per unit volume, was analysed and compared with low viscosity systems. The results revealed that a decrease in the power input caused a reduction in the growth rate as well as in production rate. It was observed that the effectiveness factor (n) both for alginate production and xanthan synthesis resulted weakly dependent on the biomass content. A good correlation between effectiveness and N-RC was obtained for the two tested models. N-RC number could be appropriately employed in correlating the effectiveness factor for processes with viscosities from 0.001 to more than 1 kg m(-1)s(-1). Due to the parallelism with the conventional internal diffusion approach (Thiele modulus), the advantages for applying N-RC in particular to correlate the efficiency in systems limited both for external convection and internal diffusional resistance, are shown. (C) 2002 Elsevier Science B.V. All rights reserved.