Mutiscale Simulation Studies Of The Micro-nano Flow And Battery

Mutiscale Simulation Studies of the Micro-nano Flow and Battery This work is supported by the National Natural Science Foundation of China(grant No. 51175223), and belongs to the study of multiscale simulations.Microfluidics and nanofluidics systems have been widely applied in the fields of national defense, medicine, biological engineering, etc. However, the complex flow of microfluidics and nanofluidics systems belongs to multiscale phenomenon. The traditional computational fluid dynamics can not be used to solve the multiscale problems. Therefore, it is necessary to develop the multiscale computer simulation method to study the complex flow phenomena in the microfluidics and nanofluidics systems. In addition, the existing power rechargeable batteries have problems such as safety, low energy density and long charging time, etc. Aluminum air battery becomes a hot research due to the advantages of high energy density, low cost, non-toxic environmental protection, etc. The multiscale phenomena of micro and nano Couette flow and diffusion flow of the microfluidic battery has been widely concerned with the commercial application of micro-nanofluidics system. In this paper, we study the multiscale simulation method of the battery and microfluidics and nanofluidics systems. The thesis topic not only has academic value for the understanding of microfluidic and battery multiscale phenomena at the molecular level, but also lays a solid foundation for microfluidic system and battery multiscale design software development. The research also has reference value on multi-scale simulation in other fields.In this paper, the main research includes the following content:1. We studied the Couette flow problems based on continuous- particle coupling algorithm. This paper discussed the degree of Continuity- Particle area different grid density on the influence of the fluid particle velocity and density using continuous-molecular dynamics algorithm. This paper studies the changes of fluid properties caused by vibration near the pipe wall. The continuous- dissipative particle dynamics method is used to examine the steady-state flow problems. Schwarz alternating method is applied to space decoupling of simulation area. This paper studies the influence of the grid size of Continuity- Particle area and shear rate on the fluid flow characteristic.2. We studied the polyelectrolyte brush grafted in nanochannel and its conformation changes using a coarse grained molecular dynamics method. The conformation changes of neutral bottle polymer brush grafted on the surface of the plate flow were studied. This paper proposes a multiscale simulation method for the flow in nanochannel grafted polymer brush. The slip length near the wall grafted polymer brush was calculated using molecular dynamics method in the micro scale, and slip length takes into the macroscopic flow calculation. The influence of different shear rate and the number of grafted polymer on the nanochannel fluid flow was analyzed by multiscale simulation.3. This paper established a hierarchical multi-scale simulation model for microfluidic fuel cell. The vanadium ion diffusion coefficient was calculated at the micro scale. Effective diffusion coefficient of vanadium ion in porous media was calculated in the mesoscopic scale with vanadium ion diffusion coefficient as the transitional information. In the macro scale, the calculation results of diffusion coefficient from the microscopic and mesoscopic scale take into the governing equation to predict the macro performance of microfluidic fuel cell by Computational fluid dynamics. The calculation accuracy is higher than that of single scale macro simulation results compared with the experimental results.4. This paper established a multiscale model of lithium air battery. In microscale, the effective diffusion coefficient of oxygen in the porous media was calculated. The influence of temperature and porous media pore size on the effective diffusion coefficient was analyzed. In the macro scale, the effective diffusion coefficient from the micro scale calculation takes into the governing equation to predict the performance of lithium air battery. The trend of the charge and discharge curves is consistent with the experimental results of the literature.5. This paper proposes a multiscale simulation method of the electrolyte solution conductivity. The radial distribution function of components particles within the KOH solution was calculated by all atomic molecular dynamics simulations at the micro scale. The mean square displacement and diffusion coefficient of charged ions take into the Nernst- Einstein equation in macro scale to predict the electrical conductivity of KOH electrolyte solution. The relationship between the mass fraction of alkaline electrolyte solution and its conductivity was studied by multi-scale simulation for the study of aluminum air battery. Therefore, the optimization of KOH solution mass fraction and conductivity best value are obtained.The aluminum air battery discharge performances respectively using pure aluminum, aluminum alloy Al7475 and Al2024 as metal anode of the battery are tested. In addition, this paper also designs an aluminum air battery solution which can be mechanically separated. It can effectively restrain self- corrosion discharge of the aluminum air battery when it’s stopping, and reduce the hydrogen evolution reaction. It is confirmed that mechanically separated aluminum air battery with Al7475 anode can effectively protect the battery capacity and improve the efficiency of metal anode by intermittent discharge.The comparative study on the continuous- particle coupling algorithm, molecular dynamics, dissipative particle dynamics and macro simulation method such as finite element method, all kinds of multi-scale simulation method and its application in the micro-fluidics and nanofluidics systems have been performed in this paper. This paper also studied the battery multiscale simulation methods by parameter passing. The understanding of microscale flow law and battery at the molecular level is of great significance for the microfluidics chip design and development of new type of battery.