| In recent years,heat pumps have received more and more attention as an energy-saving device that can increase the thermal energy grade and use electric energy to transfer heat from low-grade heat sources that cannot be directly used such as air,geothermal,and solar energy into high-grade heat sources.The air source heat pump is an energy-saving and environmentally friendly heating equipment.It has the advantages of low initial investment,quick installation,and can be used for both summer cooling and winter heating.It is widely used in the field of building energy-saving projects.However,air source heat pumps also have their limitations.After years of operating practice,it has been found that the air source heat pumps are not ideal for heating in winter.The main reason is the frosting of the outdoor unit.The frosting of the outdoor unit will affect the performance of the heat pump.The heat exchange effect deteriorates,the performance of the fan is attenuated,the equipment is damaged,the heating capacity is reduced,and the indoor comfort is seriously affected.Therefore,exploring more effective and energy-saving defrosting/defrosting methods,maximizing the stability and heating performance of the system,and ensuring the continuous,safe,efficient,and stable operation of the unit is an urgent problem to be solved at this stage.Frosting is a complex heat and mass transfer process involving phase change.The physical properties of the cold surface have a very important influence on the frosting process.This paper studies the frosting mechanism of the cold surface,from the critical radius of nucleation,Nucleus driving force,supersaturation,roughness and other factors analyze the nucleation process of water droplets on the superhydrophobic surface,the condensation morphology of the water droplets,and the heat transfer resistance between the water droplets and the superhydrophobic surface,and explore the phase change drive.The influence of force and phase change barrier on the phase change of water vapor on the superhydrophobic surface provides theoretical support for the use of superhydrophobic coatings to inhibit the growth of frost layers.The measurement confirmed that the epoxy resin + 2wt% graphene superhydrophobic coating has hydrophobicity.The coating was tested at different voltages and temperatures,and it was found that the temperature rise rate and temperature of the coating were stable with different contents of graphene.The value is positively correlated,and the electric heating coating can maintain stable resistance and good performance under low temperature conditions.On this basis,this paper carries out a simulation and comparative analysis of the frosting and defrosting process of the composite coating fin and the conventional aluminum fin.Multigroup simulation of the frosting process on aluminum surface and epoxy resin + 2wt% graphene superhydrophobic coating surface under different air relative humidity,ambient temperature,and air flow rate.It is found that the super-hydrophobic composite coating fin can delay the growth of the frost layer on the surface of the outdoor unit heat exchanger fin,and the amount of frost is less,and the frost suppression effect is obvious.The defrosting process of the composite electric heating coating and the conventional reverse cycle defrosting are theoretically analyzed,and the defrosting energy source and energy dissipation distribution of the two are given.The aluminum surface and the epoxy resin + 2wt% graphene superhydrophobic coating are simulated.The defrosting process of the two defrosting methods under the same frost layer thickness on the surface of the layer,the defrosting time used by the two defrosting methods is obtained,and the energy consumption of the two defrosting methods is compared and analyzed.The indoor comfort is less affected.Reasonable control of coating defrosting power and defrosting time can reduce energy consumption to a minimum,and the energy-saving characteristics of coating defrosting are obvious. |
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