Streamline variable-amplitude sine/cosine-shaped wavy fin for round tube fin heat exchanger

Disclosed is a streamline variable-amplitude sine/cosine-shaped wavy fin for a round tube fin heat exchanger. According to needs of surface extending of fins and fluid flow guiding, streamline convex waves 4 and streamline concave waves 5 with integral cross sections in sine/cosine shapes are formed through extrusion on the fins from an air flow inlet to an outlet. Connection lines of the same wave troughs and wave crests are all streamlines. The streamlines are streamlines which enable backflow at tube ends to be avoided in a direction from the tube axis to central cross section in a side channel of a tube fin heat exchanger plate fin corresponding to the fins 1. The streamline convex waves 4 and the streamline concave waves 5 vary in a mode of a proper waveform 16 along longitudinal wave amplitudes, and the wave amplitudes vary in a mode of a proper waveform 17 enveloping wave troughs and crests. The streamline sine/cosine-shaped wavy fin can effectively improve streamlines of liquid flow and reduce flow resistance; the convex/concave waves on the surface of the fin increase surface areas of the fin, therefore, the flow resistance is reduced and heat exchange capability of the fin is improved.