Abstract: In the permeable structure, which is built up of sheets, continuous channels are arranged in rows and between the rows of channels are formed flow spaces which at opposite sides are bounded bit cover plates. In the flow spaces (4) at least two successive transverse bridges (6) are arranged on the same level, the transverse bridges (6) in at least half of the sheets having a different length (B) and the channels (1) extending essentially perpendicular to the flow spaces (4).

Abstract: In the board of ceramic material for the construction of permeable structures, the board has three rows of holes which extend parallel to one another and are arranged symmetrically to the axis of symmetry. Three recesses of differing length are arranged between the rows of holes. The recesses intersect the board edge, the longest and one of the two shorter ones opening out at the same board edge and the shortest being opposite the second longest. The webs remaining between the recesses or the recess and the board edge have a length of 25%.+-.0 to 6% in relation to the length of the board determined by the direction of the rows of holes. The boards are stacked in succession to form various layers of the plate heat exchanger as the holes of the stacked boards form continuous channels and the recesses form shallow channels which extend substantially transversely to the continuous channels.