Abstract:

In order to overcome the difficulty in manufacturing pipe-wall porous grooves that possess excellent capability of heat transfer enhancement,first,a ploughing-heat treatment method was proposed,by which grooves were manufactured on the inner surface of a copper tube by ploughing and a porous layer was formed on the groove surface via the heat treatment in hydrogen environment. Next,the surface morphology of the porous grooves was observed by means of SEM and was further analyzed. Then,the formation mechanism of the porous grooves was investigated based on the plastic deformation theory and the thermal vacancy transition theory,finding that the proposed ploughing-heat treatment method helps to successfully fabricate porous grooves on tube walls,and that,with the comprehensive action of thermal energy and hydrogen disease during the heat treatment,the formation of porous grooves is mainly due to the complex influences of both the micro-crackers and the lattice defects of groove surface occurring in the ploughing process. Finally,all these above-mentioned findings were verified by metallographic analysis.

Key words: enhanced heat transfer, ploughing, heat treatment, microstructure, porous groove