The Mechanism Analysis And Experimental Research Of The Electrostatic Field Strengthening The Mass Transfer In The Solution-air System

Entering the"14th Five-Year Plan",the goal of“CO2 emission peak”and“carbon neutrality”puts forward an urgent need for energy conservation of building and HVAC.The brine solution is not limited to the dew point temperature and avoids reheating when handling humidity.At the same time,it can be regenerated by solar energy and waste heat.Therefore,the energy saving potential of the liquid desiccant system is huge,and how to strengthen the solution dehumidification and regeneration is one of the major research issues in recent years.The electric field has been applied to strengthen evaporation,heat transfer and drying because of its easy adjustment and low energy consumption,whereas there are few studies on the influence of electric field on the gas-liquid mass transfer in liquid desiccant system,and the mechanism of its influence is still unclear.Therefore,the experiment of dehumidification/regeneration of LiCl solution under two types of electrostatic field is carried out,analyzing the strengthen mechanism from the aspect of the microscopic characteristics of LiCl solution and water molecular migration.The detailed researches and results are as follows:Firstly,the methods and principles of molecular dynamics were summarized and combed.In order to ensure the accuracy of molecular dynamics simulation,the thermodynamic properties of LiCl solution were simulated by using the software of GROMACS.The simulation results were compared with the experimental results,and three commonly used parameters describing the interaction forces of Li⁺,Cl^-were evaluated.The Koneshan model was finally selected to simulate the microscopic characteristics of solution and water molecule transport process under electric field because of its best simulation value of surface tension.Secondly,the structure characteristics and energy changes of LiCl solution after adding electric field were explored by using the Koneshan model.The results were mainly analyzed from the radial distribution function,interface layer thickness,dipole orientation of water molecules and potential energy changes.It is found that after adding electric field,particles in interface layer will increase,and H₂O molecules will be easier to escape from the solution into gas phase.In addition,the oxygen atoms in H₂O are closer to Li⁺according to radial distribution function,and the distribution of the overall hydration structure of ion-water can be obtained on the basis of the orientation angle of H₂O molecules around Li⁺,Cl^-.However,the electric field can not affect the tight hydration layer between the ions and water.The absolute values of van der Waals force energy and Coulomb interaction energy and the surface tension of the solution decrease with the increase of the electric field strength.The reason can be obtained from the increase of the total z-axis dipole moment,that is,the polar water molecules tend to rotate in the direction of the electric field of z-axis,turning part of the repulsive force into gravitational force.The rotation of water molecules will also change the position of ions,thereby reducing this two kinds of potential energy and the force between the particles,which brings about the reduction of surface tension.Then,the electric field was applied to the LiCl-H₂O system in order to more intuitively explore the transport behavior of H₂O molecules and its dipole orientation in the transport process,which provided a basis for further research on the mechanism of electric-field enhancing solution dehumidification/regeneration.Increasing the field strength,it can be found that when the electric field reaches 2 V/nm,the two-phase system of solution and water will change from the original independence to rapid and violent fusion.With the accumulation of time,the number of water molecules migrating back and forth will gradually increase,but in general,the number of negative migration is higher than that of positive migration.That is to say,the migration of water molecules from water to the solution is strengthened,and the angle between the H₂O dipole orientation and z-axis of in the process of migration is majorly distributed in the range of 20°-60°,so the orientation of water molecules is confirmed again.Finally,the feasibility of enhancing solution dehumidification by electric field was verified by the experiments.The high voltage parallel electric field on the air side was applied to the LiCl solution-air system to explore the changes of dehumidification and regeneration.After several controlled experiments,it is found that the dehumidification and regeneration did not show obvious rules with the increase of voltage.Hence the high voltage electric field can not affect the dehumidification and regeneration of LiCl under the experimental conditions.Through thermodynamic and electrodynamics analysis,it is found that the layout and strength of parallel electric field is the main reason.Therefore,the experiments of dehumidification/regeneration with charged thin films put on the interface were carried out as another experimental scheme.The foam metal film was selected to explore the variation of dehumidification rate with or without conductive film.It is found that the introduction of positive or negative electrodes can enhance mass transfer in both dehumidification and regeneration conditions.That is to say,the original trend of mass transfer is enhanced,and the degree of negative electrode enhancement is higher.The change of surface tension plays a major role in mass transfer after the introduction of electrodes.