Study On Fabrication And Heat Transfer Performance Of Enhanced Boiling/Condensation Tube With Hydrophilic/Hydrophobic Surface

The development of energy-saving technology and further improvement of energy efficiency are conducive to the realization of China’s energy strategic objectives.Heat pump is the main equipment to replace boiler in the coal-to-electricity projects.It has the integration of refrigeration and heating,and its core component,heat exchange tube,is required to have excellent boiling performance and excellent condensation performance.However,due to the difference of enhanced boiling/condensation principle,the manufacture of new enhanced boiling/condensation tube is a challenging topic.Therefore,this paper proposes an enhanced boiling/condensation tube with hydrophilic/hydrophobic surfaces.Based on the threedimensional structure of the surface of the enhanced tube,the hydrophilic/hydrophobic surfaces are designed and prepared.The preparation scheme of the hydrophilic/hydrophobic surfaces with high coverage and high stability is explored,and the boiling/condensation heat transfer performance and enhancement mechanism of the enhanced tube with hydrophilic and hydrophobic surfaces are studied.The main research contents are as follows:The enhanced boiling/condensation tube was manufactured by rolling cutting extrusion method,and the structure parameters with the best boiling/condensation performance under R134 a working medium were explored by orthogonal experimental design.On the basis of the boiling/condensation enhancement tube with optimal structural parameters,a hybrid hydrophilic/hydrophobic surface was designed and fabricated.The hydrophilic and hydrophobic surfaces were characterized by contact angle meter and scanning electron microscope,and the coverage and stability of the hydrophilic and hydrophobic surfaces at different treatment concentrations were tested.Pool boiling and condensation heat transfer experiments were set up to study the pool boiling/condensation performance and bubble/droplet behavior of enhanced tube with hydrophobic surface and smooth tube with hydrophobic surface,and to analyze the heat transfer mechanism of hydrophobic surface and three-dimensional structure.The pool boiling heat transfer experiment results show that the comprehensive enhanced boiling performance of the enhanced boiling/condensation tube with outer hydrophilic and inner hydrophobic surface is the best,the boiling heat transfer can be effectively enhanced at low heat flux,the incipient boiling superheat can be reduced,and the enhancement effect is stable at high heat flux.Through the visualization of boiling bubble behavior,it is found that the bubbles on superhydrophobic surface are easier to detach from the surface,the superhydrophobic surface tends to form a continuous vapor film,and the detachment size of bubbles can be effectively controlled on the outer hydrophilic and inner hydrophobic surface due to its spaced hydrophilic and hydrophobic regions.According to the experimental results of condensation heat transfer,enhanced boiling/condensation tube with superhydrophobic surface and internal hydrophobic and external hydrophilic surface had the best condensation heat transfer performance.Under the experimental conditions,the condensation heat transfer coefficient outside the tube can reach2-2.6 times of that of the untreated smooth tube and 1.1-1.4 times of that of the untreated enhanced boiling / condensation tube.Through the visualization of the condensation process,it is observed that the surface of superhydrophobic and internal hydrophobic and external hydrophilic surface enhanced boiling/condensation tube presents drop shape.The main mode of droplet detachment from boiling/condensation enhanced tube with super hydrophobic surface is droplet bounce,while the mode of droplet detachment from the hydrophilic region is droplet diversion.Two efficient droplet separation modes make the tubes with these two surfaces have excellent condensation heat transfer performance.