outside of the tubes the manifolds receive ends of the tubes and have an inlet and an outlet for introducing the first fluidum into the flat tubes and for discharging therefrom each manifold has at least two adjacent parallel channels with a partition wall therebetween each channel is further defined by at least a second wall with at least part of the second wall having a curved surface the partition wall defines two parallel substantially flat surfaces facing the channels each channel has a perimeter in cross section defined by a continuous line having curved and straight portions application_number US 48615304 A description referring to fig1 the illustrated heat exchanger includes a plurality of flat heat transfer tubes 1 stacked in parallel and corrugated fins 2 sandwiched between the flat tubes 1 the ends 1 a of the tubes 1 are connected to manifolds 3 and 4 each heat transfer tube may be made of extruded aluminium having a flat configuration alternatively the flat tubes can be multi bored flat tubes commonly called multiport tubes or else electrically seamed tubes can be used multiport tubes may be made by extrusion but otherwise it is possible to make such tubes by rolling from clad sheet folding and brazing furthermore it is possible to use a welded.