A heat exchanger comprising a first tank, a second tank, and a plurality of flat heat transfer tubes connected to the first tank and to the second tank, placing the pair of tanks in fluid communication. The heat exchanger further comprises at least one rib extending from one of an outer surface and an inner surface an inner surface of one of the plurality of flat heat transfer tubes and at least one stopper extending from the outer surface of the one of the plurality of flat heat exchanger tubes. Each of the at least one stoppers is positioned between one of the at least one ribs and one of the first tank and the second tank.