The geometry is specified in the interface with the
surfaceAreas[nHT], the roughnesses[nHT]
and the lengths[nHT] along the flow path. Moreover the fluid flow
is characterized for different types of devices by the
characteristic dimensions[nHT+1] and the average
velocities vs[nHT+1] of fluid flow. See
Pipes.BaseClasses.CharacteristicNumbers.ReynoldsNumber for
example definitions.