Effect Of Janus Particles On Boiling Heat Transfer

With the high integration of electronic components and the rapid development of 5G intelligence,improving heat dissipation performance has become a problem that must be solved for the further development of these high-tech products.As an efficient heat transfer method,boiling heat transfer is of great significance to break through the heat management problems in high-tech.The boiling heat transfer performance is related to factors such as particle wettability and the number of surface nucleation points.In order to break through the bottleneck of particle-controlled boiling heat transfer technology,From the perspective of bionic function synergy,this paper innovatively proposes a scientific idea of enhancing boiling heat transfer with amphiphilic Janus particles(partially lyophilic and partly aerophilic on the particle surface).Firstly,the amphiphilic Janus particles were prepared,and the impact of Janus particles on bubbles was observed visually under cold conditions,and the mechanism of its behavior was analyzed by force.Innovatively added it to water-based pool boiling for experimental exploration,Subsequently,the preparation method of micron-sized Janus particles,the effects of particle size and different hydrophilic side contact angles on heat transfer performance were explored.The specific research contents and achievements are as follows:Pioneered the study of the interaction of amphiphilic Janus particles with air bubbles in the cold state was taken.Using Janus particles with a diameter of 1.0 mm,the dynamic behavior characteristics of particles hitting bubbles at different dimensionless drop heights were studied,involving visual observation and theoretical analysis.Through high-speed visualization and theoretical deduction,it is found that when the hydrophilic side and the interface of Janus particles contact the bubble,the particle will rotate on the surface of the bubble,but when the hydrophobic side contacts the bubble,there will be no rotational motion.The origin of the rotation of Janus particles on the bubble surface was revealed by force.The reason was that the direction and action point of the capillary force on the hydrophilic side and the hydrophobic side are different,which will generate a rotational resultant torque,which will cause the Janus particles to rotate.The effects of Janus particle layer number(1-3 layers)and liquid subcooling on boiling heat transfer were explored.The working fluid used was deionized water,and the diameter of Janus particles was 1.0 mm.The results showed that the critical heat flux(CHF)and heat transfer coefficient(HTC)were significantly improved by adding Janus particles,among which the CHF of the three-layer Janus particles was increased by 54.7%compared with the smooth surface,which was the largest increase.The enhanced heat transfer effect was the best when there were 2 layers of Janus particles,and the HTC was increased by 106.3%.In the pool boiling with 1 layer of 1.0 mm Janus particles added,the cases of subcooling at 10 ℃,20℃and 40 ℃ were studied,and the CHF increased with the increase of the supercooling degree.When the supercooling degree was 40 ℃,CHF increased by 204.7%compared to saturated boiling.The effects of micron Janus particle size(400-800 μm)and wettability matching parameters on boiling heat transfer were explored.On the basis of millimeter-scale Janus particles,micron Janus particles were further prepared,and the pool boiling test device was improved.It is found that the ZnO-N(superhydrophilic-superhydrophobic)Janus particles with a particle size of 600 μm have the most obvious effect on enhancing heat transfer,and can increase the HTC of the smooth surface by 103.4%.At low heat flux,for 600 μm Janus particles,reducing the contact angle of the hydrophilic side from 80.4°to close to 0°,the effect of enhancing heat transfer is slightly improved,because reducing the contact angle of the hydrophilic side of Janus particles has an enhanced effect on boiling heat transfer Affected by the combined effects of wall superheat,bubble escape diameter and frequency,CHF increased by 8.28%with the decrease of contact angle.