Experimental Study On Enhanced Condensation Heat Transfer By Synergistic Drainage Of Superhydrophilic Mastoid Surfaces And Combined Surfaces

Steam condensation is widely used in industrial production and life.Normally,superhydrophobic surfaces have a high condensation heat transfer coefficient.However,some studies have pointed out that in pure steam environments,such as heat pipes or high-efficiency industrial condensers,the phenomenon of "pinning" of droplets will occur on some superhydrophobic surfaces,making it difficult for droplets to fall off,which will adversely affect the heat transfer of condensation.Therefore,in order to increase the droplet detachment frequency of the superhydrophobic surface in a pure steam environment,based on the cooperative drainage idea,a double-layer composite surface was designed and fabricated,which realized the liquid collection and drainage functions of the condensing surface,and strengthened the condensation heat transfer performance.It is of great significance to improve the economy and safety of industrial production.Firstly,a superhydrophilic tapered mastoid array surface is prepared by powder sintering and chemical oxidation technology.The mastoid peaks are directly contacted with the superhydrophobic surface to discharge droplets on the condensed surface and increase the renewal frequency of the condensed surface.The steam condensation heat transfer experiment results show that the superhydrophilic mastoid surface has good liquid drainage ability,which improves the detachment speed of the "pinned" droplets on the superhydrophobic surface and the spreading liquid film on the smooth copper surface,reduces the condensation heat resistance,and strengthen the condensation heat transfer performance.The experimental results show that after adding the superhydrophilic mastoid surface,the condensation heat transfer coefficient is up to 2.12 times that of the smooth cuprum surface.Secondly,on the basis of the superhydrophobic surface,a hydrophilic-superhydrophobic striped surface was prepared.During the condensation process,the steam condenses into droplets in the superhydrophobic area and grows up continuously.When the droplets contact the hydrophilic area,the wettability gradient of the hydrophilic-superhydrophobic stripe surface will drive the droplets to move to the hydrophilic area to realize the droplets transfer and collection.Make the hydrophilic stripes directly contact the peaks of the mastoid,so that the collected condensate is discharged through the mastoid.which strengthens the droplets collecting capacity of the hydrophilic-superhydrophobic stripes surface and the drainage capacity of the mastoid.The condensation heat transfer experiment on the mastoid-striated double-layer combination surface shows that the hydrophilic-superhydrophobic stripes surface and the superhydrophilic mastoid surface have a good cooperative drainage ability.which further enhances the condensation heat transfer performance and condensation heat transfer.The coefficient is up to 3.33 times that of a smooth cuprum surface.Finally,inspired by the field of boiling heat transfer,the copper mesh covered surface was prepared by thermal diffusion technology,which bonded the copper mesh to the condensing surface,and superhydrophobic modification technology.It is found that there is a special behavior of droplets on the copper mesh covered surface:the droplets penetrate the copper mesh under the action of Laplace force,so that the small droplets on the entire surface converge into a large droplet.Therefore,the liquid collection range of the condensation surface extends from the vicinity of the hydrophilic area to the entire condensation surface,which further enhances the drainage capacity of the mastoid.The condensation heat transfer experiment shows that the copper mesh covered surface and the superhydrophilic mastoid surface have a better cooperative drainage ability,which greatly enhances the condensation heat transfer performance.The thermal coefficient is up to 3.64 times that of a smooth cuprum surface.In summary,the double-layer composite surface proposed in this paper realizes the cooperative drainage process.The liquid collection of the condensation surface and the drainage design of the superhydrophilic mastoid surface can increase the condensation heat transfer coefficient by 264%,which provides a new method and idea for strengthening the performance of condensation heat transfer.