(57) A counter-current heat exchange element, in particular for a central heating boiler,
comprising a substantially flat box-shaped body (1) containing a water passage (5),
the flat side walls (1a, 1b) of said body (1) being provided with protrusions (6)
extending into flue passages (9) on both sides of said body (1) and being arranged
according to a pattern of laterally offset rows with the lateral spacing of said protrusions
(6) gradually decreasing from the high temperature area towards the low temperature
area in each flue passage (9), the water passage (5) extending along a serpentine
trajectory between a cool water inlet (2) in the low flue gas temperature area and
a heated water outlet (3) in the high flue gas temperature area, the water passage
(5) narrowing from the inlet (2) towards the outlet (3) in such a manner that the
water flow velocity at the outlet (3) is higher than at the inlet (2).
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