Combined Internal and External Transport Limitations

Normally the phenomena of external and internal mass transport cannot be treated as completely separate. Theoretically, separation of these two effects may be difficult, but experimentally it is quite possible to create conditions in which (a) the effect of external transport is negligible (by increasing the relative fluid velocity) or (b) the effect of internal limitation is minimal (by reducing particle size). Generally, however, both phenomena must be taken into con- 

After calculating the modulus (j) by assuming a value for Cg, rj may be found from existing charts (Atkinson, 1974 Moo-Young and Kobayashi, 1972). As the true value of Cg must be found by an iterative procedure, Equ. 4.102 holds only for one particular value of Cg.  

A more straightforward method for determining Cg is a graphical method that uses the existing rj. charts (Frouws et al., 1976). Defining a normalized mass transport rate, f][, in contrast to which is a dimensionless reaction rate 

The behavior of this type of equation can be shown graphically by plotting fcapp against Sl,b log-log diagram. Fig. 4.42 (Watanabe et al., 1980). 

The case of coupled external and internal transports has also been dealt with by Reuss (1976), who proposed a graphical solution to the problem, assuming saturation kinetics for the respiration of pellets and defining an overall transfer coefficient 

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