Preparation Of Superhydrophobic Materials By One-Step Method And Its Dirt Accumulation And Heat Transfer In The Gas With Dust And High Humidity

With the expansion of urbanization in China,the sludge production is increasing.Untreated sludge has a high content of toxic and harmful substances,which will do harm to people and the environment.So,treatment of sludge brooks no delay.Sludge drying and incineration is an advanced method in sludge treatment,but this process also has the problem of large energy waste.Especially concentrated in the sludge drying stage,in which most of the energy will be wasted in the form of sludge drying tail gas.It is very meaningful to recover this heat.However,as the sludge drying tail gas has high humidity and dust,the traditional stainless steel heat exchanger is often blocked due to the accumulation of wet dust,resulting in the overall shutdown of the plant.It also brings huge economic cost and delays the sludge treatment process,so it is necessary to solve or alleviate this problem.Super hydrophobic materials have excellent self-cleaning and waterproof properties.When there is a inclination,water droplet is easy to roll off the surface.And the dust adhering to the super hydrophobic surface is easy to be cleaned by the falling water droplets,so its application in the heat exchange of sludge drying tail gas is expected to solve or alleviate the problem.The methods for preparing super-hydrophobic surface include wet chemical etching,spraying,laser ablation,sol-gel,electrochemical deposition,etc.Comparatively,the wet chemical etching is considered to be a promising method for large-scale application because of the low cost and simple operation.In this article,we report a novel method to create super-hydrophobic stainless steel with one-step wet chemical method and reveal the mechanisms of reaction.Currently,there are few reports about that.The results of the orthogonal experiments indicated that:（1）the ratio of H₂O₂/HF was the most significant factor affecting the hydrophobicity of stainless steels（SLS）,（2）In order to obtain good hydrophobicity,the addition of H₂O₂ should be controlled in the range of H₂O₂/HF=0.2/1-0.4/1.And the best sample has the maximum WCA of 161.78°and the minimum SA of 1.94°.（3）With the increase of H₂O₂ content,the surface roughness of SLS firstly increased and then decreased and the phenomenon shows that the moderate H₂O₂ will accelerate etching while the overmuch H₂O₂ will counteract.（4）The Fenton reaction between H₂O₂ and HF is the key to improve modification effect.（5）Meanwhile,the samples prepared by one-step method also showed good durability and corrosion resistance.The hydrophobicity of the optimal sample（SS5）was stable during exposure in the ambient air for 3 months,and the corrosion rate was only 1/6 of the raw SLS.A medium-sized heat exchange device was further designed and built,which is mainly composed of heating part,humidification part,dust feeding part,heat exchange part,data acquisition part,and the device can accurately control temperature,humidity and the dust concentration of gas.The scaling and heat transfer experi ments of super-hydrophobic SLS and ordinary SLS were completed on the device.The results show that the heat transfer of superhydrophobic stainless steel is better than that of ordinary stainless steel whether there is dust or not in the wet gas mixture.When operating under the condition of high humidity and dust（the flow rate from 4m/s to 6m/s）,the amount of dust scaling of super hydrophobic SLS is 23%lower than that of ordinary SLS and 22.6%lower than that from 60 to 80℃.