Experimental Study On The Effect Of Surface Treatment Technology And Applied Magnetic Field On Frost Formation

Frosting is a common phenomenon in nature and engineering.In engineering application,frost will increase the heat transfer resistance of heat exchange surface,cause COP decline of cooling system,cause great impact on the normal operation of wind power,photovoltaic power generation,transmission cable and other infrastructure facilities;in aerospace,frost will cause the aircraft safety reduction,affect the normal operation of satellite solar panels and normal operation of space station combination,and cause great safety risks to property safety of aircraft and astronauts.Traditional frost technology is difficult to operate in special circumstances,and will lead to greatly reducing the stability of the system,causing a large amount of energy loss,so it is important to study and develop effective and feasible frost suppression methods.The current research focuses on the impact of surface wetting on the frost process,and the frost properties are not only affected by the surface contact angle,the surface structure and outer field are also important factors affecting the frosting process.Frost suppression research should not be limited to routine frost suppression conditions,frosting often occurs in extreme environmental conditions such as ultra temperature and high humidity,so it is necessary to study the surface characteristics and the frost suppression effect of the external field affected by the environmental conditions.This paper studied the physical properties of the frost layer,using microscopic visualization methods,the influence of magnetic field strength,surface wetting and surface structure on frost process are studied,the specific research contents as follows:1.This paper studied the frosting process of 3 surfaces(CA=48°,CA=76°,CA=133°)at different magnetic field strengths(B=0Gs,B=180Gs,B=380Gs)under relative humidity(RH=65%,RH=75%,RH=90%)at different cold surface temperatures(T_w=-10?,-20?,-35?).Established a micro-visual observation experiment platform,using the image binarization data processing method,analyzed the magnetic field strength and surface wetting on condensate bead size,droplet crystal time,droplet and frost crystal coverage,frost crystal morphology,frost layer thickness and density,and obtained the change of frost characteristics with magnetic field strength and surface contact angle.The results show that under T_w=-20?and RH=65%,compared with the ordinary bare aluminum surface,the particle diameter of the condensate bead on the hydrophobic surface decreases by about 30%,the crystallization time extends by more than 350s,and the distribution of the condensate bead is more sparse;the thickness of frost layer and frost crystal density decreases with the increase of magnetic field strength and contact angle.2.The change of frost forming process,and the frost suppression effect of hydrophobic surface and magnetic field under different cold surface temperature and environmental humidity are analyzed.The results show that with decreasing cold surface temperature and increasing air relative humidity,the early water growth merger stage of frost is shortened,frosting rate and frost crystal coverage are increasing,thickness of the frost layer is higher,frost deposition is increasing,frosting density increases with the decrease of cold surface temperature and environmental humidity.Lower T_w and increased RH lead to the reduced effect of the external magnetic field and surface wetting on the frost process,as the phase transition driving potential increases under low temperature and high wet conditions,the small diameter water beads are easy to condense and freeze in surface microstructure gap,lead in poor hydrophobic effect;the magnetization of the magnetic field is reflected in destroying the hydrogen bonds of liquid water,the reduced droplet condensation stage before the frost causes magnetic field magnetization time reduced,the influence of the magnetic field on the frost-forming process is greatly weakened;the effect of T_w and air RH on frost suppression effect of hydrophobic surface is greater than that on frost suppression effect of magnetic field,with increasing surface contact angle and magnetic field strength,the more obvious frost suppression effect is affected by environmental conditions.3.The frosting process of micronano composite surface is studied,the frosting status and defrosting characteristics of micronano composite structure surface and wetting surface were compared.Two kinds of parallel microgroove structure aluminum surfaces(mechanical groove surface,3-stage micro-nano composite structure surface)were prepared by precision machining and chemical etching.The frost properties of 3-stage micro-nano composite structure surface with hydrophilic surface,bare aluminum surface,hydrobic surface and mechanical groove surface under different environmental conditions were compared,and the defrosting properties of cold surface and drainage properties of defrosting water under natural conditions were investigated.The experimental results show that the 3-stage micro-nano composite structure surface has obvious effect of frost suppression and excellent drainage.The results of the frosting and defrosting cycle experiments were found that 3-stage micro-nano composite structure surface can maintain low frost density after 5 frost frost cycles,proving that the micro-nano composite structure surface has stable durability.