Investigation Of Condensation Heat Transfer Enhancement For The Self-Assembly Monolayer Surfaces

The heat transfer of steam condensation has broad application in the field of spaceflight, power production and chemical industry. The improvement of the heat transfer property of steam condensation also has a significant meaning in saving energy sources and the project expenditure. Dropwise condensation (DWC) has a larger heat transfer coefficient and is the best approach to enhance heat transfer by means of interfacial properties. This paper mainly focuses on the mechanism of the microstructure, surface free energy difference effect on heat transfer.This thesis concentrates on achieving dropwise condensation through self-assembled monolayers (SAMs). The author has found out the best way of SAMs base on the existing experimental condition, and the contact angle of the SAMs is 163.0°on average, contact angle hysteres is less than 5°.A conclusion is drawn that the temperature is the key factor of SAMs formation.The pre-treating of SAMs can greatly affect the results, the SAMs on oxidized copper surface has a larger contact angle compared with the SAMs on plain copper surface.Two different types of SAMs coatings with different pretreatment have been analyzed experimentally for their ability to promote DWC. The contact angle of coated surface was 116°(hydrophobic surface) while that with nanostructure was 165°(super-hydrophobic surface). Heat transfer on coated surfaces indicated that the super-hydrophobic surface with nanostructure did not have a positive effect on DWC compared with hydrophobic surface. The research indicated that nanostructure did not promote DWC heat transfer but the interfacial interaction including liquid-solid surface free energy difference and contact angle hysteresis was the essential factor.The effects of SAMs of n-octadecyl mercaptan coatings heat treatment on the condensation modes and heat transfer characteristics of dropwise-filmwise coexisting condensation were investigated experimentally. The results show that the condensation modes transform from filmwise to dropwise on SAMs with different heat treatment temperature. The transition condensation heat transfer is also affected by gradual change of solid-liquid free energy difference reflected by condensation mode.