Molecular Dynamics Simulation In The Application Of Direct Air Dehumidification By Electrodialysis Method

With the improving of life,people's demand on standard of indoor air environment is increasing.With respect to this,the influence of temperature and humidity is the key factor.For the operational process of existing air conditioning equipments,the temperature would be reduced when achieving the required humidity.Consequently,they need to conduct a reheating process to reach the designed temperature of supply air.So this will lead to energy consumption.Therefore,In order to achieve independent control of environmental temperature and humidity,researchers have been always researching and improving the existing independent processing technology of air conditioning.This work is using the technology of both electrodialysis and membrane separating to assist the process of air dehumidification.Due to the fact that water vapor is electronegative,the technology of electrodialysis could be able to promote the diffusion of water molecules,which is a fundamental step for dehumidification.However,applying electric field directly has not been widely used in the field of dehumidification,thus this work adopts the method of molecular dynamics to simulate the process to study corresponding theoretical basis.The main research content is following:Firstly,it is a critical step to choose the membrane material suitably for membrane separation,according to property of matter.In the aspect of inorganic membrane,graphene oxide is a cost-effective membrane material,it has excellent performance in mechanical property and chemical stability.This work explores the effect of electric fields on the process of water vapor molecules diffusion in graphene oxide membrane and evaluates the differences regarding ratio of C/O of graphene oxide membrane.The results reveal that as the electric field intensity increases to 109V/m,the diffusion coefficient of water molecules achieves highest,with the numerical value three times higher than that under no electric field.It is because that high electric field will induce the dipolar orientation of water molecules tend to the orientation of electric field intensity,thus it brokes some of the original hydrogen-bonding so that it benefits the water molecules diffusion.Meanwhile,when water vapor molecules diffusing correapondingly in the ratio of graphene oxide membrane which of C/O of 0.2,0.3,0.4,the rangeability of diffusion coefficients of water molecules first increase and then decrease.Especially for the C/O ratio of graphene oxide is 0.3,the diffusion effect is the significant under specific electric fields.It is due to the increasing of the C/O ratio,it not only promotes the hydrophilic property of graphene oxide membrane,but also reduce the diffusion space of water molecules.Secondly,polyimide is a favorable material of membrane separation of gas in the aspect of polymer,the structure of which contains nitrogen aromatic heterocyclic of polymer.It is superior in permeability and selectivity.This work is to study the process of water molecules diffusion in polyimide membrane under different electric fields.Also it compares with the process of water molecules diffusion in graphene oxide to choose the best material of membrane in the field of electric field.The results show that when the electric field intensity is respectively set to OV/m,106V/m,107V/m and 109V/m,with the increase of electric field intensities,the diffusion coefficient of water molecules in the polyimide increasing.However,the rangeability of diffusion coefficient of water molecules diffusion in polyimide is two times of that under no electric field.The order of magnitude of water molecules diffusion coefficient in graphene oxide and polyimide differs by 3.The reason is that the oxygen-containing functional groups of graphene oxide is conductive to increase the number of water molecules in membrane,as comparing with polyimide membrane.Thirdly,in the practical application,influences of environment conditions to dehumidification cannot be ignored.Especially under the circumstance of high humidity and temperature,the operation efficiency of most dehumidification devices decrease.In this work,we also explore the influence of temperature and humidity to water molecules diffusion in the graphene oxide under the effect of electric field.Results indicate that when the temperature changes from 270K to 300K or the relative humidity changes from 30%to 80%under the effect of electric fields,the influence of either temperature or humidity on the diffusion coefficient of water molecules no longer accords with the study researchers did before under no electric fields.Expecially under the circumstance when temperature is 300K or relative humidity is 60%,the water molecules diffusion under electric fields is remarkable.For one side,the effect of electric field will influence the Brownian motion of water molecules.For the other side,the diffusion space of water molecules in membrane is limited.Last but not least,according to the statistical results under different operation condition,and comparing with that under no electric fields,high electric fields have most significant influence on the increase of the water vapor diffusion coefficient.This would establish the base of theoretical basis for future experiment.This work demonstrates the technology of electro-dialysis is promising for dehumidification of air conditioning.