Analysis of the great variety of now-injection (FI) manifolds used in
analytical practice nowadays has shown that most of them can be decomp
osed into two basic now configurations, i.e., the single-line and the
conjugated two-line system. The former system has one influent and one
effluent stream through which it can contact with the environment. Th
e conduit walls are totally impermeable. The most distinctive characte
ristic of a conjugated two-line system is the existence of a now-throu
gh section with two separate streams (e.g., donor and acceptor) which
exchange matter continuously along a common semipermeable interface (e
.g., membrane). It can be concluded that two of the cornerstones in th
e modelling of FI manifolds are the successful mathematical descriptio
n of the two basic now systems mentioned above. Numerous mathematical
models of FI systems employing ideas from different scientific areas (
e.g., statistics, chemical engineering, artificial intelligence, chrom
atography) have been developed so far. It should be pointed out that t
he majority of them describe only single-line FI systems. A classifica
tion of all these models based on the main principles on which they ar
e built, is proposed. The models have been compared with respect to th
eir predictive power, the complexity of their mathematical treatment,
and the requirements for computation time when applied to single-line
and conjugated two-line FI systems. It is concluded that the axially d
ispersed plug now model deserves special attention because it offers a
n acceptable compromise between the conflicting requirements for maxim
al possible mathematical simplicity and maximal possible precision. It
can be used as the basis for an unified approach to the modelling of
FI systems.