Heat transfer pipe for liquid medium having grooved inner surface and heat exchanger employing the same

A heat transfer pipe for conducting heat exchange with movement of a liquid medium therein, comprising:

• annular or spiral grooves formed on an inner surface of said heat transfer pipe, said grooves being continuously formed at a predetermined interval in a longitudinal direction of said heat transfer pipe:
• wherein an extending direction of said grooves is inclined at an angle of more than 50°, but no more than 90° with respect to an axis of said heat transfer pipe,
• wherein a ratio W/P of a bottom width W of a projection formed between said grooves to said groove pitch P is 0.1 to 0.9.