For a well defined counter flow with a uniform distribution of the flow
over the cross section of the recuperator we need an array of parallel
ducts, in which a duct carrying the primary medium is surrounded by
ducts carrying the secondary medium, whereby the pressure difference
over the ducts is much larger than in the header distributing the media
over the ducts. The geometry of the recuperator has to be symmetrical,
so each duct has the same length and the pressure drop and the flow is
the same for each duct, including the headers. Even if the headers are
symmetrical, the different lengths of the trajectories of both headers
induce a flow difference as the viscosity and velocity are not the same in
both headers, causing more inhomogenity if the temperature difference of
the supply media increases.
The flow regime has to be reproducible, which is satisfied by a laminar
In a uniform counter flow, temperature difference between primary and
secondary medium is the same anywhere in the recuperator, leading to
optimum use of the recuperator material, see fig. 1.
Figure 1 counter flow (left) and cross flow (right) recuperator
In the uniform counter flow recuperator, the temperature difference is
anywhere the same and smaller than in a cross flow recuperator, leading
to a better effectiveness and less material use for the walls.