denote mass flow functions of feeding,
internal and external processes, respectively. Subscript l denotes
a number of granular materials. Subscript k is a number of particle
class and subscript j denotes number for both external and internal
processes. The upper limit of internal processes is equal to NI and
for external processes equaled NE. The unknown distribution function
occurs inside mass flow balance of external and internal processes. As
an example, the mass flow of an internal processes could calculate
according to the following formula Eq. (2):