Study On Heat Transfer And Bubble Kinetics Of Micro And Nano Surface Boiling Based On Self-wetting Solution

As an efficient and stable heat transfer method,boiling heat transfer is widely used in many fields.In recent years,many domestic and foreign scholars have developed new technologies to enhance boiling heat transfer.The development of micro-nanoporous films and material modification technologies make it possible to maintain the nucleate boiling region with high heat transfer coefficients for a long period of time,and the wettability of the working medium al so has a great effect on the boiling heat transfer performance.Many scholars have affirmed the enhancement of boiling heat transfer on micro-nano surfaces and self-wetting solutions,however,the effects of coupling on heat transfer performance has rarely been examined.In this paper,a new enhanced boiling heat transfer technology is proposed,ie,the surface of the nanotubes is the heating surface,and the self-wetting solution is used as the heating medium.Heat transfer characteristics between the coupled heat transfer and the conventional smooth surface and distilled water heat transfer was compared by pool boiling experiments.Based on the experimental data and theoretical knowledge,the heat transfer mechanism of nano-surface and self-wetting solution was analyzed,and the dynamic analysis of bubbles generated at different working conditions was performed.Highly ordered nanotube titanium plate surfaces were prepared in organic and inorganic electrolytes respectively by anodic oxidation.The morphologies of nanotubes surfaces and smooth surface were characterized by Scanning Electron Microscope(abbreviated as SEM),Atomic Force Microscopy(abbreviated as AFM)and Automatic Contact Angle Measuring Instrument,preparing self-wetting solution and measuring the surface tension and viscosity of the solution.According to the measurement results,choosing the appropriate concentration of nanometer surface and self-wetting solution to prepare for the later experimental study.The heat transfer performance of different heating surfaces(smooth surface and nano surface)with different working fluids(de-condensation distilled water and different concentration of self-wetting solution)was investigated by pool boiling experiment.The result shows that the coupling of the nano surface and the self-wetting solution could start the system boiling at a lower overheat and improve the heat transfer coefficient and the critical heat flux.And the heat transfer performance of the system gradually decreases with the increase of the concentration of the self-wetting solution.The coupling effects on the maximum HTC and CHF of the system are slightly different,showing a synergistic enhancement of boiling heat transfer characteristics.The main reason for strengthening the heat transfer performance of the system is that the coupling heat transfer has small bubble diameter,high separation frequency,micro bubble phenomenon and special effective liquid supplement path during the boiling process.The effect of the nano surface and the self-wetting solution on the heat transfer performance was further analyzed from the bubble behavior which was recorded by the combination of high speed camera and cold light source.When compared with the smooth surface,the bubble on the nano surface is smaller and the frequency of detachment is higher.The bubbles produced in different working fluids were analyzed by non-uniform and constant speed forces.The relationship between drag coefficient and Re number,We number and Eo number was investigated.Based on the experimental data,the modified expression of drag coefficient model is deduced by the analysis method of Buckingham theorem.The comparison of the fitting formula results and experimental values at different stages under different working fluids,the error of the non-uniform section is less than 10%,and the error of the uniform velocity section is less than 5%.