4. Influence of internal convective flow on internal efficiency

Convective flow can occur within a porous grain in two cases.

• In the first case, the catalytic reaction is not isochoric and, if the transfer of constituents into the pores is not exclusively of the Knudsen type, the molar barycentric velocity $\overrightarrow{u}$ of all constituents is not zero. In this case, a div. term ( $\overrightarrow{u}$ C ′ ) must be added to the balance equations.

• In the second case, where the porous grain has macroporosity, external convective flow generates a pressure...