No abstract

Liquid-solid mass and heat (by analogy) transfer at the bottom of a cylindrical stirred vessel were studied by using the well-known electrochemical technique. Variables studied included the impeller geometry and its rotational speed. Results revealed that the radial flow impeller is preferable over the axial flow one in terms of mass transfer enhancement, additionally, increasing the impeller rotational speed led to an increase in the mass transfer coefficient. Results were correlated by dimensionless equations. Application of these equations in the design and operation of an improved catalytic biochemical reactor suitable for conducting diffusion-controlled immobilized cell (or enzyme) reactions was highlighted. These equations can serve in predicting the corrosion rate and corrosion allowance required to calculate the bottom thickness of the agitated vessel in its design stage. Furthermore, these equations can be used in estimating the heat lost from the tank bottom, accordingly, design an effective cooling jacket surrounding the agitated vessel bottom in case of exothermic biochemical reactions to avoid thermal degradation of the biomass.

In an attempt to obviate the costly and protracted separation of final products from powdered catalyst particles in stirred slurry catalytic reactors, the electrochemical technique was used in the present study to determine mass transfer in a stirred vessel equipped with different baffle configurations placed at the tank bottom. Additionally, the effect of baffle tube diameters, as well as the impeller speed and geometry were examined. Mass transfer data obtained were correlated using the governing dimensionless groups from which heat transfer rates can be deduced by analogy. Results revealed the merits of using tubular baffles in terms of mass transfer and consequently heat transfer enhancement. Besides acting as a catalyst support where liquid-solid diffusion-controlled catalytic reactions, electrochemical reactions, photochemical reactions, and immobilized enzyme-catalyzed biochemical reactions take place, a tubular baffle can act also as a built-in cooler, in case of highly exothermic reactions to avoid hot spots and catalyst deactivation.