Co-Current, Counter-Current and Cross-Flow are three important process configurations when there are multiple flows of media into one or more reactors.
Co-Current and Counter-Current configurations are both applicable to units with two phases entering and leaving a plug flow reactor. Co-current units have both phases entering one end of the reactor and both phases moving in parallel through the reactor and then leaving the opposite end. Counter-current units have the two phases entering at opposite ends of the reactor, moving through the reactor in opposite directions and then leaving the opposite end that each phase entered. For a single CSTR, where the phases enter has no impact as a result of the perfect mixing within the reactor assumption.
Cross-flow configuration is applicable to the flow behaviour through multiple units. In cross flow, one phase moves through a sequence of reactors in series while the second phase moves through the multiple units in parallel.