| Frosting is a common phenomenon in air conditioning,aerospace and other fields,which adversely affect the normal operation of heat exchange equipment.In serious cases,it causes damage to the equipment itself and increase the operation and maintenance cost of the equipment.In recent years,the researchers use a lot of methods to deal with frost on the surface of the equipment problems,such as on heat exchanger heater installation,ultrasonic defrost defrost and magnetic field,etc.,these methods to the problem of frost formation on the surface of the heat exchanger play a positive role,but the extra defrosting device increased the equipment cost and operation cost,and increase the device which needs to be maintained,makes the equipment system more complicated.Therefore,it is necessary to study the mechanism of frost formation and frost suppression on cold surface and to prepare heat exchanger materials with frost inhibition properties from the perspective of materials themselves.Study shows that the surface characteristics of the heat exchanger surface frost/frost suppression process have different impact,for studying the characteristics of different surface of frost and the influence of frost suppression is grim,structures,taking the frost test bench,the use of semiconductor refrigerating unit to provide cooling capacity on the surface of the test,the characteristics of different surface frost on the surface of the metal/frost suppression process visualization research,of which is prepared by chemical etching-boiling water oxidation with surface micro structure of micro-nanometer composite structure,respectively to investigate on the surface of the hydrophilic and hydrophobic surface water meter cream suppression performance.In order to investigate the effect of hydrophilic metal surfaces on frosting and defrosting processes,the frosting/defrosting processes on bare aluminum surfaces,rough surfaces and corroded surfaces are experimentally studied.The results show that the frost crystal growth height on bare aluminum surface is higher than that on corroded surface and rough surface during the first frost process.During the secondary frosting process,the defrosting droplets on the bare aluminum surface gathered locally and the frost crystal height increased obviously.Due to its hydrophilic property,the corroded surface exhibits good frost inhibition performance.On the rough surface,the frost grains are small and evenly distributed along the plane direction,forming a denseand hard "ice surface".During the two defrosting processes,the average defrosting time of the corroded surface is 38.2% less than that of the rough surface,indicating that the corroded surface with hydrophilic property had better frost suppression performance.In order to reveal the mechanism of frost suppression on superhydrophobic surface.Superhydrophobic aluminum surface with micro-nano composite structure is prepared by chemical etching.The frosting process was observed by microscopic visualization on the refrigeration test bench and the frosting crystal evolution is analyzed.The cold surface temperature of the superhydrophobic sheet is set as-5?,-10? and-15? respectively.By comparing the frost-crystal height and frost-crystal mass on the surface of ordinary aluminum sheet and superhydrophobic aluminum sheet,the frost-crystal height and frost-crystal mass on the surface of ordinary aluminum sheet and superhydrophobic aluminum sheet are explained by combining phase transition kinetics,classical nucleation theory,heat and mass transfer theory.Under different experimental stages and different experimental temperature conditions,the anti-frost effect of the superhydrophobic aluminum surface itself is different,but compared with the anti-frost characteristics of ordinary surface aluminum,the superhydrophobic aluminum surface has a certain anti-frost effect,the overall frosting process lags behind;The frost layer height developed relatively slowly.After 10 min of experiment,the frost layer height on the superhydrophobic surface is only 35% of that on the ordinary surface.Because condensate beads form Wenzel state on the cold surface,and water droplets are infiltrated in the micro-structure,under certain conditions,the superhydrophobic aluminum surface can effectively delay the formation of condensate beads,thus inhibiting frosting;In the late frosting period,when the condensate is frozen and covered with frost crystals on the surface,the frost suppression effect is relatively deteriorated;Common aluminum surface after modified by lauric acid also has a certain inhibitory frost performance,but the effect is very weak from super hydrophobic surface with micro-nano composite structure,it is recommended that in making a frost demand suppression of material surface,can be to delay the birth of the condensed water bead into technical means,make suitable surface micro structure,in order to achieve maximum suppression frost.A large number of studies show that the superhydrophobic surface has a broadapplication prospect in frost suppression.However,its interface characteristics have not been reported on the thorough mechanism of frost suppression,and the frost suppression performance under different working conditions,especially under the influence of haze,is hardly been systematically studied.In this paper,chemical etching-oxidation method is used to simplify the preparation of superhydrophobic aluminum base surface.Through theoretical analysis,it is found that the superhydrophobic surface with micron and nano-composite structure constructed on the metal surface has the best anti-frost performance,which can not only delay the formation of condensate beads,but also reduce the freezing rate of condensate beads.In order to systematically study the frost suppression performance of the superhydrophobic surface,frosting experiments are designed under different conditions with or without haze.It is proved its excellent ice-proof performance.Under the influence of haze,although the tiny particles in haze increased the formation rate of condensate beads,after the experiment is carried out for 15 min,the frost crystal height on the superhydrophobic surface is only 24.5% of that on the ordinary surface,and the frost suppression effect is obvious.Therefore,a simple,low-cost and efficient method is proposed to make the application of superhydrophobic surfaces in a wide range of fields a reality.Figure [26] table [3] reference [81]... |
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