Clover heat exchanger core

A heat exchanger comprising a plurality of elongate parallel fluid medium conducting tubes, a first fluid handling means communicating with the opposite ends of the tubes to deliver a first fluid medium into one end and to receive said medium at the other end thereof, a second fluid handling means directing a second fluid medium about the exterior of and between the tubes, each tube is formed with an uneven number of circumferentially spaced longitudinally extending grooves and circumferentially spaced longitudinally extending lobes, each lobe occurs between a pair of adjacent grooves, the grooves have concave substantially radially outwardly disposed outside bottom surfaces and the lobes have substantially radially outwardly disposed convex outside surfaces, the radius of said convex surfaces is less than the radius of said concave surfaces, the lobes at the sides of each tube projecting toward adjacent tubes extend to the related grooves of said adjacent tubes with the concave and convex surfaces of the related lobes and grooves in spaced relationship.