The numerical modelling of system is nowadays a useful tool in order t
o improve the understanding of its operation and its CAO design. We pr
esent here the different numeric approaches realised to obtain a minim
al and operating model, on a industrial computer (PC), of a complex th
ermal system : the spiral plate heat exchanger. We describe the spiral
plate exchanger; then, we describe two steady-state numerical modelli
ng of heat exchange : finite differences and Galerkine finite elements
methods which are used with several computing options. With these mod
els, we can study the performances in steady-state operation and the s
ensitivity with geometrical and physical parameters variations.