Heat exchanger with flow obstructions to reduce fluid dead zones

The invention relates to heat exchangers including plate pairs having a rib design which results in reduced fluid dead zones, particularly in heat exchangers having U-shaped flow passages for a liquid. An example of such heat exchangers is an Exhaust Gas Heat Recovery (EGHR) heat exchanger. The presence of dead zones into the circulating fluid in such heat exchangers, not only degrades the overall heat transfer coefficient, but also increases the risk of coolant boiling. The heat exchanger of the present invention comprises: at least one plate pair (10, 18) comprising a first plate and a second plate; a fluid flow passage (20) for flow of a first fluid defined between the first plate and the second plate; an elongate flow barrier (54, 56) separating the fluid flow passage of each said plate pair into an inlet portion (58), and an outlet portion (60), wherein the flow barrier extends from a first end (50) of the plate pair to a terminal end (64) proximate to the second end (52) of the plate pair, and wherein the flow barrier includes a gap (62) allowing fluid flow communication between the inlet portion and the outlet portion of the fluid flow passage; and a crescent-shaped flow obstruction (66, 68) located in the gap of each said plate pair, the flow obstruction having arcuate first and second sides (70, 72) describing a portion of a smoothly rounded shape.