Research On Condensation Heat Transfer On Superhydrophobic Surface With Micro-nano Structure

Condensation heat transfer is widely used in chemical industry,power generation,seawater desalination,refrigeration and other fields.Compared with traditional film condensation,droplet condensation has higher heat transfer efficiency.Recent research results show that dropwise condensation on the surface of heat transfer can be maintained by using superhydrophobic surface,thus improving the efficiency of condensation heat transfer.The micro-geometrical structure of superhydrophobic surface will affect the size distribution,bouncing frequency and growth evolution of droplets during condensation,thus affecting the overall heat transfer performance of the heat transfer surface.Therefore,it is of great scientific significance and application value to study the effects of different micro and nanostructures on heat transfer enhancement on superhydrophobic surfaces.In this paper,silicon wafers with different geometric parameters were fabricated by photolithography and ion etching.The surface free energy of microstructured silicon wafers was reduced by immersion in nano-solution,and superhydrophobic surfaces with different microstructures and nanostructures were obtained.In this paper,two experimental methods were used to study the effect of micro and nanostructures on heat transfer enhancement on superhydrophobic surfaces.On the one hand,micro-condensation experiments were carried out on different superhydrophobic surfaces using optical microscopy,and the effects of Micro-Nanostructures on the wetting characteristics of initial condensation and the size distribution of condensate droplets during the growth process of superhydrophobic surfaces were studied.On the other hand,macro-condensation experiments were carried out on vertical superhydrophobic silicon wafers in a constant temperature and humidity chamber for different condensation strips.The number,diameter distribution and dropping frequency of condensate droplets per unit area under the work piece were analyzed and counted.On this basis,surface heat transfer was studied using droplet heat transfer model.The effects of contact angle,wetting state and thermal resistance of different microstructures on the heat transfer of a single droplet are analyzed.The results show that the superhydrophobic surface with secondary structure can increase droplet falling frequency,reduce droplet size and improve condensation heat transfer efficiency.