Heat transfer tube for single phase flow

A heat transfer tube for single-phase flow having at least one row of projections formed on the inner surface of said heat transfer tube along at least one spiral curve, said at least one row of projections having a plurality of projections formed discontinuously, portions of the inner surface of the heat transfer tube between adjacent rows presenting surfaces parallel to the tube axis, each of said projections has a cross-section constituted by smooth curves at any portion along a height thereof including the bottom thereof, a cross-sectional area of said projections progressively decreases toward the top thereof, said projections have a height of 0.45 to 0.6 mm and are arranged at a circumferential pitch of 3.5 to 5 mm and an axial pitch of 5 to 15 mm, said heat transfer tube has porous heat transfer surfaces formed on the outer surface of said heat transfer tube, said porous heat transfer surfaces having a plurality of tunnel-shaped parallel cavities in outer surface portions thereof, a plurality of openings formed in ceiling portions of said plurality of said tunnel-shaped cavities, a spiral groove is formed on an outer surface of the heat transfer tube and extends across said plurality of tunnel-shaped cavities, said spiral groove being formed when said projections are formed at the inner surface of the heat transfer tube, and wherein each of said plurality of tunnel shaped cavities opens in a direction of the spiral groove at an intersection of the spiral groove with the respective tunnel shaped cavities.