1. Transfer across a fluid-solid interface

In an article dedicated to transfers within solid products, it is of prime importance to determine under which conditions (operating parameters, product properties) these internal transfers control the process speed (are limiting). To this end, we compare the values of the transfer resistances defined on either side of the solid-ambient fluid interface. From the product's point of view, these resistances are referred to as internal and external. If the resistance on the solid side (internal) is greater than the resistance on the fluid side (external), transfers within the solid (internal) will be limiting, while transfers between the solid surface and the ambient fluid (external) will be limiting. It is important to note that species transfer by permeation (under total pressure gradient of the fluid phase, cf. [F 2 000], § 2.2.2...