The invention relates to a plate-type heat exchanger comprising a stack of double-walled heat exchanger plates (30 32) which are permanently interconnected and each include two plate members (33, 34) having a central heat transfer portion (35) and an edge portion (36) bent upwardly with respect to the plane of the central heat transfer portion (35), separate flow passage spaces for at least two heat exchange fluids being defined between the double-walled heat exchanger plates (30 32), the two plate members (33, 34) entering into close mutual engagement at least partly in the area of the central heat transfer portion (35) and the upwardly bent edge portion (36) yet permitting heat exchange fluid between the plate members which gets to the upwardly bent edge portions (36) to exit through an aperture between the upwardly bent edge portions (36), the upwardly bent edge portions (36) being formed respectively with an outer edge (33a, 34a). The respective outer edges (33a, 34a) of the two plate members (33, 34) of the double-walled heat exchanger plates (30 32) are spaced from each other.
