Preparation And Condensation Characteristics Of Superhydrophobic Surface Of Cold Radiant Plate

Although radiant air-conditioning system has the advantages of high energy efficiency,high thermal comfort,low noise and so on,its cold surface condensation problem of radiation heat transfer seriously restricts the engineering application of radiant air-conditioning system.Therefore,it is urgent to solve the problem of condensation on the cold surface of radiation heat transfer.At present,the condensation problem of the cold plate surface is mostly solved by raising the dehumidification capacity of fresh air and increasing the cold plate surface temperature,which will increase the energy consumption of system operation and reduce the cooling capacity of radiant air-conditioning system.Based on the wettability of the cold plate surface,this paper studies the inhibitory effect of superhydrophobic cold surface on condensation,mainly focusing on the condensation characteristics of superhydrophobic surface and the condensation nucleation of surface water vapor.Firstly,the cylindrical array microstructure is manufactured on the surface of aluminum alloy by laser engraving,and then the rough surface is modified by low surface energy materials,so that the aluminum alloy surface has superhydrophobic properties and the surface contact angle exceeds 150 °.The effect of microstructure parameters and low surface energy substance on the surface contact angle was investigated,so the preparation process was optimized and the aluminum alloy surface with excellent hydrophobic properties was selected.Secondly,the condensation characteristics of superhydrophobic surfaces were analyzed by building a visual experimental platform to observe the condensation process.The experimental results show that under the same experimental conditions,among the prepared hydrophilic,hydrophobic and superhydrophobic aluminum alloy surfaces,the start time of condensation of superhydrophobic aluminum alloy surface is the latest,which is 3 minutes and 2.5 minutes later than that of hydrophilic and hydrophobic surfaces.In the same condensation period(within 20minutes),the area proportion of droplets covered on the surface superhydrophobic aluminum alloy surface is 19.7%,which is lower than 86.7% of hydrophilic aluminum alloy surface and41.7% of hydrophobic aluminum alloy surface.It indicates that superhydrophobic aluminum alloy surface has good dew suppression performance.In addition,the effect of temperature and humidity on the condensation characteristics of superhydrophobic surface was investigated.The results show that the area proportion of droplets and the average radius of condensate droplets increase with the decrease of cold surface temperature.In the early stage of condensation,the area proportion of droplets covered on the surface and average droplet radius increase with the increase of air relative humidity.But the condensation droplet coalescence and falling off occur frequently in the later stage of condensation,the area proportion of droplets covered on the surface under different humidity tends to be the same and stable at about 25%.Finally,based on Gibbs free energy theory and molecular dynamics theory,a theoretical model of water vapor condensation nucleation is established.The effects of surface contact angle,cold surface temperature and dew-point temperature on liquid core volume,critical nucleation free energy and nucleation rate were studied.