CFD Simulation Of Flow And Dispersion Process Of Droplet Impacting On The Stainless Steel Wire Mesh

Rotating packed bed(RPB),as a new type of multiphase flow reactor,has excellent multiphase mass transfer performance that is about 1 ～ 3 orders of magnitude larger than the packed column.The liquid in the RPB reactor was captured,sheared,and broken into small droplets,ligaments and liquid films by stainless steel wire mesh packing.These resulted in the significantly increased gas-liquid contact area and updated gas-liquid interface,which was beneficial to intensify the mass transfer process.However,the visualization technology based on optical photography was hard to obtain the dispersion mechanism of droplets on the surface of wire mesh due to the packing’s lighttight feature and small size of droplets during rotating.It seriously hindered the design and optimization of the wire mesh packing for the RPB reactor.In this work,a physical model of single-layer woven wire mesh was established,and the flow and dispersion process of liquid droplet impacting on the stainless steel wire mesh was studied by computational fluid dynamics(CFD)simulation.The visualized results under the same experimental conditions were compared to verify the accuracy of the CFD simulation method constructed in this work.The effects of initial droplet velocity,mother droplet diameter and wettability of wire mesh on droplet dispersion were investigated,and the effect of different operating conditions on the microscopic characteristics of liquid film on wire mesh surface were also studied.The main research contents are as follows:(1)Due to the advantages of CFD simulation,the cone angle of dispersion in any direction and real-time gas-liquid contact area can be obtained.Thus,the dispersion efficiency of droplet can be more accurately evaluated.The cone angle of dispersion and increased rate of gas-liquid contact area increased with the increment of initial droplet velocity,mother droplet diameter,and wettability of wire mesh surface.In comparison with the droplet impacting on the hydrophilic wire mesh,the cone angle of dispersion increased by 43 ～ 103% and the final increased rate of gas-liquid contact area increased by 1.2 ～ 5.1 times for the hydrophobic wire mesh at the same initial droplet velocity.Furthermore,at the same mother droplet diameter,the cone angle of dispersion increased by 37 ～ 62% and the final increased rate of gas-liquid contact area increased by 1.6 times.Meanwhile,the mechanism for droplet broken to strengthen the liquid dispersion was further revealed from the perspective of energy conservation.Compared with hydrophilic wire mesh,the total dissipation energy ratio of droplet impacting on the hydrophobic wire mesh was reduced by 29%,indicating that droplet can convert more energy into liquid surface energy and lead to a better liquid dispersion.(2)A thin liquid film was formed during the droplet impacting on the stainless steel wire mesh.The liquid film was further dispersed into droplets,so the understanding of liquid film flow pattern was very important.The results showed that the dynamic behavior of liquid film on the wire mesh surface can be divided into the following three steps:(i)spreading step;(ii)shrinkage process;(iii)stabilizing or disappearing step.Compared with hydrophilic wire mesh,the final wetting area of hydrophobic wire mesh was close to zero.The average liquid film thickness over the hydrophilic wire mesh was 30.02 ～ 77.29 μm,while the average liquid film thickness over the hydrophobic wire mesh was 41.76 ～ 237.37 μm.