Molecular Dynamics Simulation Of Gas Adsorption And Diffusion Charcateristics In Electrodialysis Air Direct Dehumidification System

Aiming at the low efficiency and high energy consumption problems common in traditional dehumidification technology,considering the electronegativity of water molecules and the application of external field technology in the field of heat and mass transfer in recent years.A direct air dehumidification method based on electrodialysis was proposed.This work combines electrodialysis technology and membrane separation technology to discuss the direct dehumidification process of electrodialysis air.Based on the effect of electric field has not been widely used in the field of dehumidification,so that this work adopts the method of molecular dynamics to simulate the process to get a corresponding theoretical basis.The main researching content is the following:Firstly,in order to study the diffusion characteristics of H₂O in the separation membrane under the electric field,the membrane and gas molecule models were simplified,and the diffusion characteristics of charged water molecules in nanoporous graphene membranes under different electric field intensities were studied based on the Einstein formula and Boltzmann function model.The results show that with the electrical intensity increased from 0 to 10⁵ V/m,the diffusion coefficient of H₂O in membrane increased approximately20 times.Nevertheless,which decreased rapidly after further increasing the electric intensity,indicating an optimal electric field intensity in this process.Through molecular potential energy analysis,it is concluded that when the field strength is less than 10⁵ V/m,the electric field mainly reduces the hydrogen bond and electrostatic action between water molecules.Otherwise,the electric field potential energy increases exponentially with the increase of the field strength,and the electric field force takes the lead role.In summary,the diffusion behavior of H₂O was influenced by intermolecular forces and dipole orientation,and the final equilibrium state of the H₂O was the result of the coupling of the forces.Secondly,considering that the same electronegative oxygen molecules in the air will affect the dehumidification efficiency,a nanoporous graphene oxide membrane was used to study the adsorption and diffusion characteristics of H₂O and O₂ under different electric field intensities based on the concentration distribution curve and surface diffusion coefficient.The results show that the molecular diffusion behavior is mainly related to the action intensity of the molecules on the GO membrane surface.The electric field can accelerate the desorption process,which greatly reduces the overall adsorption of gas molecules and accelerates the gas molecules into the permeate side.Moreover,the electric field is more conducive to promoting the penetration process of H₂O.There are competitive adsorption properties between H₂O and O₂,and the gas molecule diffusion and adsorption process have a relevant coupling.The molecular permeability depends on the adsorption strength and diffusion rate of gas molecules.In the mixed gas adsorption model,the optimal electric field strength exists at 10⁵ V/m,in which the water molecule diffusion rate is the fastest and it shows the maximum permeability.Thirdly,since the separation membrane and environmental factors directly affect the transmission and thermodynamic properties of gas molecules,the effects of layer spacing,simulated temperature and initial gas pressure on the molecular adsorption and diffusion behavior were investigated when the electric field intensity was 10⁵ V/m,and the best combination among multiple variables were sought.The results show that the interlayer distance mainly affects the formation of interlayer hydrogen bonds,the effect of electric field makes the transmission competition between gas molecules obvious,and the membrane separation mechanism changes from preferential adsorption to sieve effect.Moreover,there is an optimal interlayer distance of 12.5(?),which makes the H₂O penetration effect the most obvious.The temperature mainly affects the free thermal motion of the gas molecules and the hydrogen bonding effect.The action of the electric field causes the polar water molecules to rotate in the direction of the electric field to enhance the order of the H₂O,while the temperature increase destroys the order.Under the combined influence of temperature and external electric field,a mutual equilibrium state point(namely 320 K)will appear,making the diffusion effect most obvious.The pressure mainly affects the collision frequency of gas molecules and the way of hydrogen bond formation.The effect of the electric field causes the hydrogen bond formation conditions to be destroyed,but the increase in pressure reduces the distance between molecules,which is conducive to enhancing the interaction between molecules and the membrane surface.There is an optimal pressure value of 1 P,which makes the diffusion rate of H₂O the fastest.Last but not least,according to the statistical results under different operating conditions,compared with that under no electric fields,the increasing value of the diffusion coefficients of water vapor molecules is biggest in the effect of high electric fields,which is the base of theoretical basis of experiment.It means that the technology of electro-dialysis is conductive to dehumidification of air conditioning,which might be a part of the technology of dehumidification in the future.