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Southwest University of Science and Technology (2021)

Study on Wettability Control and Heat Transfer and Water Harvesting Characteristics of the Biomimetic Desert Beetle Coating

陈鑫涛

Titre : Study on Wettability Control and Heat Transfer and Water Harvesting Characteristics of the Biomimetic Desert Beetle Coating

Auteur : 陈鑫涛

Grade : Master 2021

Université : Southwest University of Science and Technology

Résumé partiel
Dew and frosting is one of the common phenomena in nature,often bring a lot of trouble to life and production,such as low temperature heat exchanger cooling fin surface of the dew or frost layer if not timely removal,will greatly increase its energy consumption.In recent years the bionic desert beetle hybrid wettability structure has been widely reported,condensation,this kind of structure can use hydrophilic area make the dew of rapid nucleation and the hydrophobic area make the dew of rapid stripping.It not only reduces the surface condensate,but also increases the nucleation rate of the droplet,and increases the droplet condensation and phase change heat transfer,which is a new idea to improve the condensation heat transfer and water collection efficiency.However,most of the methods for preparing the hybrid wettability surface of beetle bionic are complex,highly dependent on equipment,narrow adjustable range of wettability,high cost and long cycle.So based on the hybrid wettability structure of desert beetle back to inspire,we design a simple spray method to prepare the superamphiphilic-superamphiphobic hybrid wettability coatings by controlling the mass ratio(MR)of superamphiphobic Si O2 nano-powder and superamphiphilic gypsum micro-powder.The hybrid wettability coating of hydrophilic and superdiphobically surface is constructed,which overcomes many shortcomings of the existing methods for preparing hybrid wettability structures.The influence mechanism of the content of hydrophilic particles on the wettability,condensation characteristics,condensation heat transfer characteristics and water harvesting characteristics of the coating was emphatically studied.The formation and migration mechanism of condensate and the frost resistance and ice resistance ability of the coating were explored.The wettability threshold value to enhance the condensation heat transfer and water harvesting efficiency of the coating was explored.The main results are as follows :(1)By adjusting the mass ratio of gypsum powder,the wettability of the bionic desert beetle coating can be controlled effectively.As the mass ratio of superhydrophobic nano-powder to hydrophilic gypsum micron powder increases from 1:0 to 1:2,the static contact angles of water,edible oil and hexadecane gradually decrease from 156.9°,153.8°and 150.1°to 146.4°,141.5°and 139.9°,respectively.,and the corresponding roll-off angles increased from 2.4°,7.2°and 9.6°to 12.1°,180°and 180°.Droplet impact test further confirmed that the dynamic wettability decreased with the increase of the micron powder mass ratio of hydrophilic gypsum.The maximum rebound height of water droplets decreased from 3.47mm(1:0)to 2.59mm(1:2),and the contact time increased from 10.6ms(1:0)to 12.8ms(1:2).(2)The effects of the contact Angle on the nucleation rate,growth rate and desorption efficiency of the dew droplets were discussed by establishing the model of nucleation,growth and desorption of the dew droplets.The results showed that the appropriate introduction of the hydrophilic region was beneficial to the enhancement of the nucleation rate and self-migration ability of the dew droplets.

Mots clés : Bionic desert beetle coating ;Wettability controllable ;Coalescence-induced self-jumping ;Delay frost ;Condensation heat transfer ;Water harvesting

Présentation (CNKI)

Page publiée le 18 novembre 2021