Abstract:Using ploughing-extrusion method, a cross-connected finned micro-grooves structure was formed on the surface of copper strips with thickness of 0.4 mm. The structure was fabricated by making ‘V’-grooves in copper strips and perpendicular ‘V’-grooves on the opposite side that intersect the first set of grooves. Micro pores appear at the intersection of these cross-connected grooves, and micro fins appear on the groove fringes. So it can be defined as ‘pore-groove-fin’ structure. The preferable ‘pore-groove-fin’ structure can be obtained under the condition that the tool edge inclination angle (χγ) is 45˚, both the major extrusion angle (γo) and the minor extrusion angle (γ′0) are 30˚, both the major formation angle (β) and the minor formation angle (β′) are 10˚, the ploughing-extrusion depth (fd) is 0.32 mm and the groove pitch is 0.4 mm on surfaces A and B. The formed included angle of groove A is 70˚, and the groove depth is 0.3 mm, while the included angle of opposite perpendicular groove B is 20˚ with the groove depth of 0.35 mm. The obtained fin height is 0.15 mm, the elliptical pore length is 0.2 mm and the width is 0.05 mm. Experiments show that fd has the greatest influence on the formation of micro pores. Bulges appear on the opposite surface B when the ploughing-extrusion depth on surface A (fdA) reaches a critical value. The ploughing-extrusion depth on surface B (fdB) has great influence on the re-growth of fin structure.

Key words: copper stripe; micro groove; fin; ‘pore-groove-fin’ structure; boiling enhancement; ploughing-extrusion