Grooved pipe is a kind of pipe with groove after rolling. Common: circular grooved pipe, oval grooved pipe, etc. it is named grooved pipe because the obvious groove can be seen in the section of the pipe. This kind of pipe can make the fluid flow through the wall of these turbulence structures, produce flow separation areas, and form vortices with different intensities and sizes. It is these vortices that change the flow structure of the fluid and increase the turbulence near the wall, so as to improve the convective heat transfer film coefficient of the fluid and the wall.

a. Rolling groove tube rolling groove tube is to roll a horizontal groove or spiral groove with a certain pitch and depth from the outside of the circular tube according to the design requirements, and form a protruding horizontal rib or spiral rib on the inner wall of the tube, as shown in Figure 1. The groove on the outer wall and the protrusion on the inner wall of the pipe can enhance the heat transfer of the fluid on both sides of the pipe at the same time. It is especially suitable for strengthening the heat transfer of single-phase fluid in the pipe and enhancing the steam condensation and liquid film boiling heat transfer of the fluid outside the pipe in the heat exchanger.

b. Spiral grooved pipe has single pass and multi pass spiral and other types. After forming, there is a groove with a certain spiral angle outside the spiral groove pipe, and there are corresponding convex ribs in the pipe. The spiral groove should not be too deep. The deeper the groove is, the greater the flow resistance, the greater the spiral angle, and the greater the heat transfer film coefficient of the grooved tube. If the fluid can rotate along the groove, the number of threads has little effect on heat transfer.

c. The cross grooved pipe is formed by variable cross-section continuous rolling. The outside of the pipe is a transverse groove intersecting the pipe axis at 90 °, and the inside of the pipe is a transverse convex rib. After the fluid flow passes through the convex rib in the pipe, it does not produce spiral flow, but produces axial vortex groups along the whole section, so as to strengthen the heat transfer. The cross threaded tube also has a great strengthening effect on the film boiling heat transfer of the fluid in the tube, which can increase the boiling heat transfer coefficient by 3-8 times.