An improved heat-exchanger of the kind including a plurality of plates each having two longitudinal edges and two transverse edges, and each formed with protruding portions, the plates being placed side-by-side in contact with one another so that at least some of the protruding portions of each plate contact those of an adjacent plate, the plates defining at least two sets of passages through which gaseous or other fluids can flow separately for the transfer of heat through the plates from one of said fluids to another, the improvement comprising
- plates of a first type;
- plates of a second type, said second type plates being mirror images with respect to the position and orientation of the protruding portions of said first type plates, and said first type plates and said second type plates being arranged in alternating order;
- unprotruded longitudinal marginal portions adjacent the longitudinal edges of each plate, said longitudinal marginal portions of each plate being in continuous abutting contact with the respective longitudinal marginal portions of one of the two immediately adjacent plates for spacing said one adjacent plate, the plates having abutting longitudinal marginal portions forming a representative pair,
- wherein the protruding portions in each plate consist of protrusions protruding to a first degree and protrusions protruding to a second degree, the protrusion distance corresponding to the first degree being one-half the protrusion distance of the second degree, the protrusion distance being defined from said longitudinal marginal portions, all the protrusions in each plate lying entirely to one side of said longitudinal marginal portions;
- said protrusions including a plurality of parallel elongated protrusions of said second degree oriented generally in the longitudinal direction and forming between the paired plates one of the at least two sets of passages the elongated protrusions on adjacent plates being parallel;
- said protrusions also including other protrusions protruding to said second degree, said other protrusions together with said elongated protrusions being in continuous abutting contact with like protrusions in adjacent plate pairs for spacing adjacent pairs, another one of the at least two sets of passages being formed between each two spaced adjacent pairs by said elongated protrusions, all of said passages extending generally in the longitudinal direction of the plates;
- and said protrusions further including planar protrusions to said first degree in each of the plates, said planar protrusions in adjacent plates forming at least two sets of plenums, one set associated with each of said sets of passages, each of said plenum sets comprising an inlet plenum and an outlet plenum, said inlet and outlet plenums being positioned proximate opposite transverse edges of the plates forming the respective set of flow passages, the fluid flow to the plenums associated with said one passage set entering and leaving the respective inlet and outlet plenums past a respective transverse edge, said plenums associated with said one set being formed between the planar protrusions of the paired plates, and the fluid flow to said another passage set entering and leaving the respective inlet and outlet plenums past a respective longitudinal edge, said plenums of said another passage set being formed between said planar protrusions of adjacent plate pairs.