ABSTRACT
The conventional formulation of the mass transfer process rate equation expresses the diffusive driving force in terms of concentration gradients or differences. For interphase diffusion, this driving force is adjusted using the equilibrium partition coefficientKij as shown below.An alternative approach is to express the flux equations in terms of fugacity instead of concentration. The driving force then becomes simply the fugacity gradient or difference. The chemical transfer rate N(mol/h) for both approaches is given by
N = Ak(Cj − Ci/Kij) = D(fj − fi). (3.1)
The theoretical and practical relationships between the mass transfer coefficient k (m/h), the areaA (m2), the concentrationC (mol/m3), the fugacity transport coefficient D (mol/Pa/h), and the fugacity of the chemical f (Pa) is the subject of this chapter. The use of fugacity is a particularly useful concept for numerous reasons.
