Heat-exchanger of plate fin type

An oil cooler having an oil flow channel and air flow channel which are arranged alternately and formed by at least three flat plates arranged in parallel with one another at a predetermined spacing and opposed side walls provided between the adjacent flat plates, wherein the oil flow channel is formed from a blank of extruded aluminum material comprising opposed side walls and a platelike connecting wall interconnecting the opposed side walls, the platelike connecting wall being provided with a number of projections, arched when seen from one side, formed by cutting the platelike connecting wall and projecting upward and downward, the arched projections on the platelike connecting wall are arranged in the front-to-rear direction to provide a plurality of projection rows, the connecting wall further having a fluid passage opposite to every arched projection, the arched projections of each row projecting upward and downward alternatively with a flat portion formed between each arched projection and the arched projection adjacent thereto in the front-to-rear direction, the upwardly arched projections and the downwardly arched projections of the rows adjacent to each other being in a staggered arrangement transversely of the rows, so that each upward projection is adjacent to a downward projection in the transverse direction,

• each arched projection of the connecting wall having a wall thickness of 0.5 to 1.5 mm, a width of 1 to 10 times the wall thickness and a height of 2 to 10 mm, and the projections are arranged in the front-to-rear direction of the exchanger at a pitch of 3 to 30 mm.