Abstract: A heat exchanger comprises a vertically arranged circular-cylindrical holder closed at its upper end and at its lower end, and a pipe coaxially arranged within the holder. A fin is secured to the inner pipe and consists of a plurality of interconnected lamellae extending radially from the pipe, the fin being helically wound around the pipe so that the adjacent lamellae of successive turns of the resulting helix overlap each other in part, viewed in the circumferential direction of the pipe. A capillary passage is located in each lamella above the surface of an underlying lamella in a position shifted with respect to the capillary passage of the underlying lamella.