a heat transfer element includes a plurality of adjacent heat transfer plates . each of the heat transfer plates has oppositely disposed first and second heat transfer surfaces and a plurality of laterally spaced notches . a first heat transfer plate of each pair of adjacent heat transfer plates has at least one tall notch and the second heat transfer plate of each pair of plates has at least one short notch , where the notch height of the tall notch is greater than the notch height of the short notch . each of the tall notches of a heat transfer plate are received in a short notch of an adjacent heat transfer plate to thereby define flow channels therebetween .