Frosting Characteristics And Defrosting Mechanism Of Aluminum Based Superhydrophobic Surface

With the influence of the increasingly tense energy situation,energy conservation has become the focus of the industrial field.In the field of refrigeration,frosting of heat exchanger will significantly increase the heat transfer resistance of fin,block the gap of fin,reduce the heat transfer efficiency of heat exchanger,resulting in economic loss and energy waste.In order to ensure the stable operation of the equipment,various frost suppression and defrost methods have been developed,but the existing methods have some limitations,such as consuming extra energy,causing temperature fluctuations and so on.Therefore,in order to improve the efficiency of heat exchanger and reduce the unnecessary economic loss caused by the frost of heat exchanger,it is necessary to improve the existing defrosting method and frost suppression method.As a new technology in the field of materials,surface modification is welcomed because of its low energy consumption,convenient operation and remarkable effect.This paper will systematically study the frosting effect of surface modification technology on the surface of heat exchanger,especially the frosting characteristics of superhydrophobic surface and the mechanism of hot defrosting.The main research contents are as follows:(1)Study on defrosting and defrosting mechanism of superhydrophobic surface:Combined with the wetting characteristics of solid surface and classical nucleation theory,the mechanism of inhibiting nucleation of superhydrophobic surface in the process of frost formation,especially in the condensation process at the early stage of frost formation was analyzed,and the shrinkage effect of defrosting water on superhydrophobic surface was analyzed from the perspective of energy.The results show that the superhydrophobic surface has a certain inhibitory effect on the nucleation of condensation droplets in the early frost stage,and with the increase of contact Angle,the more energy required for surface nucleation,that is,the more difficult surface nucleation.In the defrosting process,the increase of the contact Angle will be more conducive to the defrosting droplet shrinkage,and then facilitate the defrosting droplet removal from the surface.(2)Preparation of different wettability surfaces and study on frosting characteristics of inclined superhydrophobic surfaces: hydrophilic,bare aluminum,hydrophobic and superhydrophobic surfaces were prepared by chemical etching and hydrothermal method.Compared and analyzed the frost formation of inclined surface and horizontal surface,bare aluminum surface and superhydrophobic surface,so as to have a more comprehensive cognition of the frost inhibition effect of superhydrophobic surface.The results show that the superhydrophobic surface has a significant inhibition effect on the growth and freezing process of condensation droplets in the early frost stage.The tilt Angle has a certain effect on the surface frosting process,especially in the process of superhydrophobic surface frosting,the appropriate tilt Angle will promote the surface condensation droplets from the surface,and then achieve the effect of frost suppression.(3)Research on defrosting and drainage characteristics of superhydrophobic surfaces: Based on the visual defrosting experimental system,the effects of different surface characteristics on defrosting and drainage were compared experimentally,and the defrosting laws of different wettability surfaces in horizontal and vertical states were analyzed.The results show that: with horizontal conditions,the defrost morphology and defrost water coverage rate of different wettability surfaces are different,and the defrost droplets on superhydrophobic surfaces are the most regular,with the lowest coverage rate and the weakest viscosity.With vertical condition,the water retention and water retention rate of superhydrophobic surface are the lowest,and the experiment verifies that superhydrophobic surface has the best defrosting effect.On this basis,the effects of surface dip Angle,frosting time and the start and stop of defrosting fan on the defrosting process of superhydrophobic surface were studied experimentally.The effect of surface dip Angle on defrosting behavior of superhydrophobic surface is significant.When the surface dip Angle is greater than 30°,most of the defrosting droplets on superhydrophobic surface can fall off.It is worth noting that the defrosting wind can significantly accelerate the thermal defrosting and evaporation rate of the superhydrophobic surface in the experiment,but it also consumes extra energy.Therefore,multiple considerations should be taken into consideration in practical application.