Abstract: In a plate heat exchanger for two fluids having different flow volumes, comprising several generally rectangular heat transfer plates provided with inlet and outlet openings through its corner portions. Each heat transfer plate has a central portion and two distribution portions (15a and 16a) located between the central portion and respective inlet and outlet openings. The sizes of the inlet and outlet openings for one fluid differ from the size of the inlet and outlet openings of the other fluid. In addition, the distribution portions of the heat transfer plates provide a larger flow resistance for one fluid than the other fluid.

Abstract: In a series of heat exchange plates (5, 6), each being rectangular with ports (7, 8, 9, 10) in its corner portions, alternate plates (6) are fully sealed and coact with intermediate plates (5) to define two groups of elongated passages through which the respective heat exchanging fluids (A, B) flow. Each intermediate plate (5) is only partially sealed and defines with one of the two adjacent fully-sealed plates (6) an area communicating directly with the atmosphere, the partial sealing consisting of port sealing means (7a, 8a, 9a, 10a) interconnecting respective pairs of opposing ports to form channels through which the two fluids (A, B) flow without entering said area. The areas form paths through which any leakage of either fluid (A, B) can escape to the atmosphere, thus preventing contamination of either fluid by the other.

Abstract: In a plate heat exchanger, the heat exchange plates of which have been provided by pressing with a corrugation pattern comprising ridges (19a, 19b) and valleys (20a, 20b), the ridges and valleys of adjacent plates extend in parallel. In each plate interspace the ridges of adjacent plates abut against each other such that the opposing valleys form parallel flow passages in the plate interspace. The ridges of at least some of the heat exchanger plates are provided with depressions (21a, 21b), which form thresholds in the valleys formed on the opposite sides of the plates by the ridges. Thresholds of this kind are formed in the heat exchange plates such that they create a substantially larger flow resistance in the plate interspace for one the heat exchange medium than in the plate interspaces for the other heat exchange medium.