Hydrodynamics and local heat transfer measurements in a bubble column with suspension of yeast

Hydrodynamics and heat transfer were investigated in a 0.28 m diameter slurry bubble column for air-water-yeast cells system. Yeast cells of about 8 mum diameter were used and the effects of gas velocity and yeast concentrations were studied. Gas holdups exhibited a maximum value around a gas superficial velocity of 0.10 m/s when foam height was included. Without the foam layer, gas holdups increased with increasing gas velocity. Bubble population was measured by means of dynamic gas disengagement technique. Rise velocity of small bubbles decreased, while rise velocity of large-bubbles fraction increased with yeast concentration which was varied from 0-0.4% w/w. Local heat transfer coefficients were measured at different axial and radial locations inside the column. Heat transfer in the foam section was significantly lower than in the main slurry column. In the bulk and developing regions, the addition of yeast cells into water increased heat transfer in the center and decreased at the wall. This work is one of very few studies reported in the literature on the use of actual yeast cells in slurry bubble columns and opens up new opportunities on their potential use as bioreactors in the fermentation industries, wastewater biological treatment and other applications. (C) 2001 Elsevier Science B.V. All rights reserved.