| The shortage of fresh water resources and the various types of wastewater from coal-fired power plants have become a serious problem affecting the sustainable development of society and the ecological environment.Membrane distillation technology,as a new type of water desalination technology,is an effective method to solve such problems.However,membrane distillation technology has problems such as poor membrane performance and low membrane flux.Therefore,it is of great significance to seek a new technical route to effectively improve membrane flux and optimise membrane performance.To address the problem of poor membrane performance,the composite membrane with different parameters was prepared by combining carbon nanotubes(MWCNTs)with PVDF using a co-blending method and tested for electrical performance.The test results show that the diameter of the composite decreases,the pore size increases and the number of pores on the membrane surface increases with the addition of MWCNTs.Compared to the pure PVDF membrane,the dielectric constant of the composites was improved,which was 4.67 time s higher than that of the pure PVDF membrane.When MWCNTs were filled with 5wt%,the surface resistivity of the composite decreased to 0.97×1011Ω and the volume resistivity decreased to 0.61×1013Ω·cm,while the dielectric loss reached a maximum of 6.52%.Overall the addition of MWCNTs has enhanced the dielectric properties of the composite.To address the problem of low membrane flux,a combination of corona discharge and membrane distillation was used to study the membrane flux characteristics of the composite membrane under different voltage magnitudes,electrode structures,electrode spacing and voltage polarity,respectively.The results show that the membrane flux can be improved by applying corona discharge.The increase in membrane flux was related to the content of MWCNTs,and the membrane flux increased gradually when the MWCNTs content increased,with the maximum membrane flux at 5wt%filling;the increase in membrane flux was related to the electrode structure,and the membrane flux under the single-needle electrode was significantly higher than that under the three-needle electrode,and the average membrane flux was 1.15 times higher than that of the three-needle electrode;the increase in membrane flux was related to the spacing of the multi-needle electrodes.The increase in membrane flux was related to the spacing of the multi-pin electrodes,with the average increase in membrane flux from 0.5cm to 1.5cm being 11.77%;the increase in membrane flux was related to the voltage polarity,with the membrane flux under negative corona being higher than that under positive corona.Based on the above work,the plasma module of COMSOL simulation software was used to numerically simulate the discharge process.The simulation results show that the electric field mode and electron density at the tip of the needle are maximum as the discharge continues to develop,and the electric field mode of the needle electrode obeys a normal distribution.The electric field mode of the three-needle spacing 1.5cm electrode is 3.5×105V/m,and the electric field mode of the single-needle electrode is 5.78×105V/m,which is 1.65 times the electric field mode of the three-needle spacing 1.5cm.By simulating the electric field intensity on the surface of the film,it is concluded that the average electric field film on the surface of the film with a three-needle electrode spacing of 1.5cm is 894.44 V/m,and under the single-needle electrode is 1168.41 V/m,which is 1.31 times more than that of the three-needle electrode.Water molecules,under the action of electric field,will move in the direction of high electric field strength because they are polar molecules,which can increase the rate of water molecules through the film,thus increasing the membrane flux and mass transfer efficiencyThis paper shows that by combining DC corona discharge with membrane distillation and by modifying the PVDF membrane,the membrane performance and membrane flux of membrane distillation can be improved,therefore,the findings of this paper have some theoretical value for combining DC corona discharge with membrane distillation to desalinate brine and promote membrane flux. |
