Study On Frost Suppression Of Super-hydrophobic Surface Under The Action Of Airflow

Air source heat pump(ASHP)is the main heating method in hot summer and cold winter area,but the frost of outdoor heat exchanger in winter brings a series of problems such as increased energy consumption and performance degradation.Surface modification technology has become the focus of air source heat pump research due to its good frost suppression properties.When the air source heat pump is heating in winter,the frost on the fin surface of the outdoor heat exchanger usually includes four processes: liquid core formation,condensation growth,droplet freezing,and frost crystal growth.Among them,the condensation growth of droplets is the basis of frost formation.If the condensation droplets can be removed,frost formation can be suppressed from source.This study superimposes the effect of external airflow on the basis of surface modification technology,and uses a combination of visual experiments and theoretical analysis to study the condensation characteristics of droplets in the initial stage of super-hydrophobic surface frosting,revealing the influence of surface microstructure on droplet characteristics The morphological characteristics of super-hydrophobic surface droplets under the action of external airflow were studied,and the influence of surface characteristics and droplet characteristics on the removal of droplets under airflow was obtained.Clarified the mechanism and law of super-hydrophobic surface enhanced removal and frost suppression,which provides a new way for the exploration of efficient frost suppression technology.The specific work content is as follows:A model for merging and removing droplets in the initial condensation stage of the superhydrophobic surface frost was constructed,and the mechanism and influence of the merging and removal process for the droplet condensation stage of the super-hydrophobic surface during the initial frost stage were revealed.The energy analysis of the multi-droplet merger removal process revealed that the surface adhesion work ratio,contact angle,and solid-liquid contact coefficient are important factors influencing the droplet merger and removal process.When the contact angle of the fin surface is above 160°,the difference in the number and uniformity of the droplets has little effect on the droplet removal and removal process.Increasing the surface contact angle and decreasing the solid-liquid contact coefficient helps to promote the droplet removal process.When the surface contact angle is greater than 140°,the initial velocity of droplet removal is less affected by the solid-liquid contact coefficient.A method for enhancing the removal of super-hydrophobic surface droplets by the effect of external gas flow is proposed,and the influence and mechanism of surface characteristics and droplet characteristics on the droplet removal process under the action of air flow are studied and revealed.On the basis of the "two-circle method",a theoretical model of sliding removal and rolling removal of surface droplets under the action of external airflow was constructed.Based on the model and visualization experiments,the deformation characteristics of the droplets and the critical wind speed for removal were obtained under the action of external airflow.The results show that when the surface contact angle is 150° ± 5° and the contact angle hysteresis is 2° ± 0.5°,the average critical removal wind speed can be as low as3m/s.The index of the contact angle hysteresis coefficient is proposed,and the influence law of the contact angle hysteresis coefficient on the critical conditions and the removal mode of droplet removal under the action of airflow is revealed.The super-hydrophobic surface promotes the process of coalescence and spontaneous bounce removal of condensed droplets on the surface due to its strong hydrophobic properties,thus achieving the removal of partially condensed droplets on the surface.By designing the surface structure to increase the linear tension,the spontaneous removal process can be further strengthened and the number of condensed droplets on the surface can be reduced.On this basis,the removal of droplets is comprehensively strengthened by the action of external airflow,which can greatly improve the frost suppression effect.