Construction Of Micro/nano-structure On The Surface Of Wire Mesh Packing And Its Influence On The Liquid Flow Behaviors And Mass Transfer Performance

The rotating packed bed(RPB)is the core equipment of high-gravity process intensification technology,which drives the packing inside the rotor to rotate at a high speed through a motor.The rotating packing disperses the liquid violently,so as to enhance the mass transfer and mixing processes.After many years of research,the main structure of RPB has been basically formed,and the research focus has changed to the inner part of RPB,such as the rotor and packing.Packing,as the main filed and medium for liquid flow and mass transfer,has great influences on the performance of RPB.At the macro level,a large number of studies about the packing have been conducted,mainly containing the effects of the characteristic size(fiber diameter,pore size,and so on)of packing,install structures and forms,and materials on RPB performance.In recent years,it has also been found that the microscopic characteristics of the packing surface have significant influence on the performance of RPB.However,the internal influence mechanisms have not been understand in depth.In this work,the construction of micro/nano-structure on wire mesh packing surface and its influence on liquid flow behaviors and mass transfer process of RPB were systematically studied.Firstly,a novel strategy of constructing micro/nano-structures on the stainless steel wire mesh surface was developed,realizing the control of the surface wettability of wire mesh packing.By means of the visualization technique,the flow behaviors of liquid impacting on the single fiber,single layer wire mesh and multilayer wire mesh,as well as considering the influences of the surface micro/nano-structures,were systematically studied.Based on these,the intensification mechanisms of liquid dispersion by impacting on the wire mesh packing surface with micro/nano-structures were revealed,which can be used to guide the packing optimization and mass transfer intensification of RPB.Main conclusions are as follows:1.A novel strategy of constructing surface micro/nano-structure by organic/inorganic composites was developed,which can be used to constructe micro/nano-structures with high stability on the surface of stainless steel substrate.By controlling the mass fraction of the functional inorganic nanoparticles in organic polymer resin,the surface roughness and surface free energy of the micro/nano-structure can be changed.Thus,the surface wettability of the stainless steel substrate can be systemally controlled from hydrophilic state(contact angle of 75°)to superhydrophobic state(contact angle of 160°).The relationship between the surface micro/nano-structure and wettability was explained by using Wenzel model and Cassie-Baxter model.The application performance tests showed that the micro/nano-structures had the highest adhesion leavel 5B(ASTM D3359-17)with the substrate and could resist the violent liquid impacting under?500 times the acceleration of gravity(acceleration of?5000 m/s2).2.The liquid flow behaviors of droplet impacting on the single mesh fiber with different surface micro/nano-structures were studied by using a synchronous imaging technique with two high-speed cameras.The flow pattern was divided into three types according to the dispersion behaviors of droplet impacting on the fiber,which were defined as one droplet,one film,and two film.The spreading process of the liquid film on the fiber surface is mainly affected by the inertial force of droplet compared with the surface effect.During the shrinkage process of the liquid film,the stronger hydrophobicity of the fiber surface resulted the larger shrinkage rate of the liquid film and the shorter contact time between the liquid film and the fiber surface.These processes greatly reduced the energy dissipation during the impact process,which is more conducive to abtain more liquid surface energy after droplet impacting.3.Based on the impacting behaviors of droplet impacting on the single fiber,the dispersion process of droplet impacting on the single layer wire mesh with different surface micro/nano-structures were further studied.There were six typical stages for the droplet dispersion from contacting the wire mesh to finally dispersing into numerous daughter droplets.Comparing with the non-surface-modified wire mesh,by increasing the surface hydrophobicity of wire mesh,the cone angle of dispersion could be maximally increased by about 80%,and the dispersed droplet diameters decreased by about 70%on average.Based on data analyses,the numerical prediction models of droplet dispersion cone angle and daughter droplet diameter were thus obtained.Combined with the mass transfer experiment,the idea that droplet dispersion can increase the liquid surface area and enhance the gas-liquid mass transfer was verified.4.The studies of droplet impacting on single fiber and single layer wire mesh provided guidance for the enhancement of multistage dispersion of droplet by constructing micro/nano-structures on multi-layer wire mesh surfaces.Results showed that the dispersion performance of liquid can be further intensified by controlling the macro parameters(the number of mesh layers,mesh spacing,and mesh number)and micro parameters(the surface micro/nano-structures)of the wire mesh packing.Based on the dimensionless analyses,the predictive correlations of droplet dispersion angle and diameter were established,which have the deviations of ±10%and±15%respectively between the predicted and the experimental values.A new structure of multilayer wire mesh with surface micro/nano-structure was proposed in the cavity of RPB,which is used for multistage dispersion of liquid from the liquid distributor,so as to obtain a good initial liquid distribution.Compared with the classic RPB without built-in multilayer wire mesh,the H2S removal rate of the new structure RPB can be improved maximumly by about 108%.