Experiments And Numerical Simulations Of Pool Boiling Heat Transfer Of Super-hydrophobic Surfaces With Different Adhesion

Boiling heat transfer is an efficient heat transfer method,which has been widely used in daily life and various engineering fields.It is of great significance to improve the heat flow density,heat transfer efficiency and energy conversion rate of boiling heat transfer for the construction of a low-carbon,clean and environmental protection energy system.Therefore,higher requirements are put forward for boiling heat transfer technology.The influence of surface microstructure size and surface wettability on boiling heat transfer has been the main research focus in this field.In this paper,a combination of experimental research and numerical simulation was used to study the pool boiling heat transfer performance of different surface sizes and different adhesion surfaces,and analyze the mechanism of the influence of the difference in adhesion of super-hydrophobic surfaces on pool boiling heat transfer.Firstly,inspired by the microstructure of the surface of lotus leaf and rose petals,a series of super-hydrophobic surfaces with different adhesions were designed and prepared.The pit structures with different pitches were scanned on the laser marking machine,and the scanned copper-based surface was modified with n-dodecyl mercaptan.The super-hydrophobic and adhesion of the surface were verified by measuring the contact angle and rolling contact angle.Secondly,the heat transfer performance of the different adhesiveness super-hydrophobic surfaces was analyzed by using the self-built visual saturated pool boiling test system.The test results show that the heat transfer performance was optimal when the surface microstructure size was the smallest(10-100),the heat transfer coefficient was 2.22 times of that of the smooth surface,and the boiling starting point of the microstructured surface was 5.6 ℃ lower than that of the smooth surface.The generation and separation of bubbles on the surface of the experimental model were collected by a high-speed camera system.The results show that the vaporization core position on the surface of the microstructure was relatively fixed,while the vaporization core position on the smooth surface was randomly generated.The separation diameter of bubbles increased with the increase of wall superheat,when the separation diameter of bubbles increased,the separation frequency of bubbles slows down,and the separation frequency of bubbles on the microstructure surface was much higher than that on the smooth surface.Surface microstructure pits provided more vaporized cores for heat transfer and increased the nucleation density of surface bubbles.The microstructure of the surface can significantly enhance the heat transfer efficiency,accelerate the generation and separation of bubbles,and accelerate the heat transfer efficiency in the process of phase transformation.Then,through the comparative analysis of the heat flux density,heat transfer coefficient and bubble dynamics of the super-hydrophobic low-adhesion surface,super-hydrophobic high-adhesion surface and smooth surface,it was found that the super-hydrophobic low adhesion surface and the super-hydrophobic high adhesion surface was significantly higher than that of a smooth surface,but with the increase of wall superheat,bubble polymerization would occur on the wall surface,which reduced the heat transfer efficiency.Finally,the growth of bubbles on the super-hydrophobic low-adhesion surface,super-hydrophobic high-adhesion surface and smooth surface was analyzed by numerical simulation.The values of heat flux and heat transfer coefficient measured by simulation and experiment are basically the same.The super-hydrophobic low-adhesion surface had the fastest bubble growth,followed by the super-hydrophobic high-adhesion surface,and finally the smooth surface,which was consistent with the test results.