Study On Rolling-cutting-extrusion Forming Mechanism And Heat Transfer Performance Of Enhanced Boiling/Condensation Three-dimensional Finned Tube

Vigorously improving the efficiency of energy resource utilization is a strategic measure for developing a green economy and building an environment-friendly society.Heat pump is a kind of high-efficiency energy-saving equipment driven by electric energy and capable of obtaining low-grade thermal energy from environmental media and waste heat.With the advancement of structural reforms on the supply side,heat pumps and new heat exchange equipment are moving towards high efficiency,compactness,and integrated cooling and heating.This requires that its core heat exchange element,the heat exchange tube,has both excellent enhanced boiling heat transfer performance and excellent condensed heat transfer performance.However,the traditional heat exchange tube is only suitable for a single heat transfer working condition,and cannot meet the needs of high-efficiency integrated cooling and heating heat exchange equipment such as heat pumps.To this end,a three-dimensional integrated finned tube with enhanced boiling / condensation is designed in this paper.A roll plowing-extrusion composite forming method is proposed and a new combination tool is developed to realize the efficient collaborative manufacturing of the three-dimensional integral finned tube.The main research contents are as follows:Based on the enhanced heat transfer technology of finned tubes,an enhanced boiling / condensing three-dimensional integrated finned tube with two-dimensional spiral fins,two layers of staggered stepped lattice fins and internally threaded grooves is designed.Aiming at the problem that the three-dimensional finned tube is difficult to realize integral processing and forming due to the complicated and fine structure and the fin structure both inside and outside the tube,a roll cutting-extrusion composite forming method was proposed.The principle of roll cutting-extrusion is researched and the conditions of roll cutting-extrusion are obtained through theoretical calculation and analysis.The combined roll cutter is designed innovatively.Select appropriate process parameters based on the structural characteristics and forming conditions of the finned tube.By analyzing the formation of spiral fins and the formation of stepped lattice fins during the roll cutting-extrusion process of finned tube,the forming mechanism of finned tubes is studied.Efficient processing of enhanced boiling / condensing three-dimensional finned tubes is achieved on a three-roll diagonal mill,and the formed finned tube are highly consistent with the theoretically designed structure.Through roll cutting-extrusion processing experiments,the influencing factors of forming morphology of enhanced boiling / condensing three-dimensional finned tubes and the influence of process parameters on the fin geometry were explored.Experimental results show that excessive machining speed,excessive outer diameter of tooth cutter,and roll cutting deviation will all lead to poor fin morphology.Decreasing the number of teeth and increasing the outer diameter of the tooth cutter will cause the width of the stepped fin to increase.The height difference between the two layers of stepped fins is determined by the outer diameter of the tooth cutter and the flat cutter.The geometric parameters of the two-dimensional spiral fin are mainly affected by the parameters of the spiral fin rolling cutter.The pitch and height of the spiral fin both increase with the thickness of the rolling cutter.Through heat transfer experiments,it is verified that the enhanced boiling / condensing three-dimensional finned tube has excellent enhanced heat transfer performance under both condensation and boiling conditions.The overall condensation and boiling heat transfer coefficients of the enhanced boiling / condensing three-dimensional finned tube are 8.1 times and 5.1 times that of the smooth tube,respectively.The finned tube with moderate pitch,small step height and small width possesses better condensation heat transfer performance,whereas the finned tube with large pitch,large step height and moderate width possesses better boiling heat transfer performance.Compared with many existing evaporation tubes and condensation tubes,the enhanced boiling / condensing three-dimensional finned tube has higher condensation and boiling heat transfer performance.