Research On Anti-frosting Mechanism Of Super-hydrophobic Surface And Experimental Study On The Performance Of The Evaporator In Air Source Heat Pump

China has a vast territory,with central heating areas divided by the Qin Mountain-Huai River as the boundary.Due to the "coal to clean energy" policy in the northern region,air source heat pump is currently used as a new form of clean heating,while the middle and lower reaches of the Yangtze River are part of a hot summer and cold winter climate area.In winter,each household uses split heat pump air-conditioning for household heating.Therefore,the air source heat pump has a practical background for wide application in our country.However,when the air source heat pump is used in a low temperature and humid environment in winter,frosting is prone to occur on the heat exchanger fins of the outdoor unit,which leads to unsatisfactory actual operation results.When severe frosting occurs,the unit can even stop working.The defrosting of the outdoor unit of the air source heat pump is urgent.In order to solve the serious frosting problem of the outdoor evaporator fins of the air source heat pump in real life,this paper starts from studying the frosting influencing factors and the growth conditions of the frost layer,and improves a frost-inhibiting surface modification method to inhibit the growth of the frost layer from the root cause;Based on the analysis of super-hydrophobic frost suppression mechanism,prepare super-hydrophobic aluminum-based fins,analyze the practicability of super-hydrophobic fins(durability,self-cleaning,liquid drainage,and corrosion resistance),and analyze super-hydrophobic aluminum-based flat sheets The frost suppression effect of the initial growth stage of the surface frost layer and the frost suppression/defrost effect of the vertical super-hydrophobic aluminum-based fins were carried out related experimental studies.Firstly,according to the theoretical analysis of the super-hydrophobic anti-frost mechanism could conclude that: From the perspective of the droplet nucleation barrier,the critical radius and critical phase transition energy barrier of the liquid core on the super-hydrophobic cold surface increase,resulting in condensed droplets,it is difficult to produce super-hydrophobic cold surfaces.According to the principle of ice bridge propagation,the condensation rate of condensate droplets on the super-hydrophobic surface is slower than that of conventional cold surfaces;as air enters the microscopic micro-nano pores of the super-hydrophobic surface,the contact area of the condensate droplets on the super-hydrophobic cold surface is reduced.When the angle increases,the critical radius at which the jumping phenomenon can occur is smaller than the conventional cold surface.The droplets frequently merge,bounce,roll,and slide,which reduces the coverage of the droplets on the super-hydrophobic cold surface,and the liquid on the super-hydrophobic cold surface The droplet size is smaller than the conventional cold surface,the number is also less,and the position is unevenly distributed.Secondly,in this paper,a chemical etching method was used to successfully fabricate a super-hydrophobic aluminum-based fin with a surface micro-nano secondary structure with a contact angle of 158.3°.Through a series of practical analysis experiments,it is proved that the super-hydrophobic aluminum base has good durability,self-cleaning,liquid drainage,and corrosion resistance characteristics,which lays the theoretical research and engineering application for the practical application of super-hydrophobic aluminum base fins to outdoor evaporators of air source heat pumps basis.In order to test the frost suppression performance and defrosting effect of super-hydrophobic aluminum-based fins,this paper builds a forced convection visualization experimental platform that simulates a low temperature and high humidity environment to test the frosting and defrosting effects of super-hydrophobic aluminum-based fins.Finally,in order to experimentally verify the mechanism of super-hydrophobic frost suppression,this paper carried out experimental research on the initial growth stage of the frost layer on the surface of aluminum substrates with different wettability.The experimental results show that the droplets can only spontaneously bounce on the super-hydrophobic aluminum-based cold surface with low surface energy;and the initial factor that causes the uneven distribution,unequal size,and structural difference of the frost crystals on the super-hydrophobic aluminum-based cold surface is liquid.The self-jumping phenomenon of droplets and the uneven distribution of droplets cause uneven distribution of the frost layer.The super-hydrophobic cold surface has a much slower freezing propagation rate than the conventional cold surface.The higher the temperature of the cold surface,the better the anti-freezing performance of the super-hydrophobic cold surface.Under the experimental conditions of outdoor relative humidity of 86%,wind speed of 1.3 m/s,ambient temperature of aluminum base of 5 ° C,and cold surface temperature of-13 ° C,the time for the cold surface of super-hydrophobic aluminum base to start to frost is longer than that of conventional aluminum base.The cold surface of the flat sheet is delayed by 165 s.The average growth rate of the frost coverage of the conventional aluminum-based cold surface and the super-hydrophobic aluminum-based cold surface during the frosting process are0.643%/s and 0.15%/s,respectively.The super-hydrophobic aluminum-based flat sheet The cold surface exhibits good frost suppression performance during the initial frosting process.Aiming at the changes in thickness,weight growth,and growth rate of the super-hydrophobic vertical aluminum-based fin surface under forced convection conditions during the frosting process,the fin defrosting time and the final location of the defrosting water were experimentally studied.The experimental results show that,in the experimental conditions,the outdoor environment temperature is 7 ° C,the test environment temperature in the experiment chamber is 6.85 ° C,the relative humidity on the windward side of the fin is91%,and the wind speed is 0.6 m/s,and the relative humidity on the leeward side of the fin is77% and the wind speed.At 0.73 m/s and the cooling temperature of the refrigeration station is-18 ° C,the frosting amount of the super-hydrophobic aluminum-based fin is 69.84% of that of the conventional aluminum-based fin,and the average growth rate of the frost layer is65.22% of that of the conventional aluminum-based fin.In the outdoor environment,the time required to completely melt the frost layer of super-hydrophobic aluminum-based fins is57.69% of that of conventional aluminum-based fins,and the proportion of residual defrosting water on conventional aluminum-based fins and super-hydrophobic aluminum-based fins is76.55% and 28.70%,the super-hydrophobic vertical aluminum-based fins exhibited good anti-frosting and rapid defrosting characteristics during the entire frosting/defrosting process.