Regenerative heat exchangers

A pack of heat transfer plates for regenerative air preheaters comprising a plurality of superimposed profiled plates, each pair of plates together forming elongated, substantially straight open-ended channels for substantially free flow therethrough in either direction of heat exchanging fluids substantially without deflecting the straight flowing heat exchanging fluids flowing through said open-ended channels from their substantially straight flow path, said channels extending between two opposite end surfaces of the pack and being closed on their sides by said pair of adjacent plates, each plate being provided with a plurality of spaced sets of straight continuous parallel double ridges extending obliquely to said end surfaces from one edge of the plate to another, the double ridges of each set having opposed crests protruding symmetrically from both opposite sides of each of said plates, adjacent sets of double ridges of each of said plates being separated by separating plate portions of a width greater than the height of said double ridges above the median plane of the plate, said double ridges each having an interior wall defined by an intermediate contact pressure resisting web portion joining the opposed crests of the double ridge, said intermediate web portion being steeply sloping relative to said median plane of the plate to effectively resist the contact pressure between said superimposed plates, each ridge of said double ridges having an outer wall which extends from the respective crest to the separating plate portion adjacent the respective crest, said outer walls symmetrically sloping relative to said separating plate portion and having a substantially lower slope relative to said median plane than said intermediate web portion, said separating plate portions being provided with undulations substantially parallel with the ridges, said undulations having a ratio of undulation height over the middle plane of the plate to undulation pitch amounting to 0 to 1/6, and said plates being so disposed relative to each other that the ridges of one plate lie transverse to the ridges of adjacent plates so that the ridges of the adjacent plates cross each other at respective crossing portions of the crests of the ridges thereof, and said adjacent plates supporting each other solely by direct contact at the crossing portions of the crests of the ridges to form said flow channels between adjacent plates, the angle between the ridges and said end surfaces of the plate pack being between 40.degree. and 75.degree., and being smaller than 75.degree. when said ratio is equal to 0 and smaller than 70.degree. when said ratio is greater than 0,

• whereby each time a heat exchanging fluid flowing in a given flow channel reaches a crossing portion of the crests of the ridges of adjacent plates, the fluid is split up into sub-flows, one sub-flow portion flowing to an adjacent flow channel to at least partly be mixed with the fluid of said adjacent flow channel, and another sub-flow portion remaining in said given flow channel.