| The investigation of micro-and nanoscale liquid flow is the key for the further development of MEMS and achieving the efficient development of tight oils.Due to the small feature size,the traditional fluid mechanics method is no longer applicable,and the liquid flow must be described from the viewpoint of molecular motion.Molecular dynamics simulation is based on the potential energy model between microscopic particles,does not introduce conventional assumptions,and has unique advantages in exploring physical phenomena at the nanoscale.Based on theoretical analysis,this paper uses molecular dynamics simulation to study the flow characteristics of liquids in nanochannels,discusses the intrinsic mechanism of "microscale effects",and establishes micro/nanochannels with percolation network simulation technology.The main research contents and achievements made by the thesis are as follows:(1)Based on the classical fluid mechanics theory,the hydrodynamic equations under different boundary conditions are deduced.At the same time,the law of flow of nano-scale single-phase liquids is simulated using molecular dynamics method,and the continuous fluid mechanics theory is verified at the micro/nano scale.The intrinsic dynamic mechanism of boundary adhesion layer and velocity slip phenomenon is analyzed in essence.The boundary adhesion layer has only molecular dimensions,but the slip length is as high as nanometer level.The influence on the micro-nanoscale liquid flow can not be ignored.In addition,the velocity slip not only occurs on the fluid wall,but also has different degrees of slip within the fluid in the interface region.(2)The interaction between the fluid and the wall surface at the micro/nano scale induces changes in the liquid structure and kinetic properties,and the large specific surface area further enhances this change,mainly representing the "non-Newtonian fluid" phenomenon of the nanofluid.The effective viscosity calculation model was introduced to perfect the micro-nano scale fluid mechanics theory.At the same time,the concept of effective slip length was used to combine the boundary layer adhesion with the interface velocity slip to establish a uniform micro-nano scale fluid mechanics model and analyze it theoretically.The comparison with the data verified the validity of the model.(3)The micro-nano-scale single-phase liquid flow experiment was carried out,and the linear flow characteristics of single-phase deionized water in a micron-sized quartz tube were clarified.Based on the micro-nanoscale hydrodynamic model established in this paper,the single phase in a 1 ?m-diameter circular tube was analyzed.The reason why the liquid flow deviates from the theoretical prediction value by-60.98%.Comparing the experimental results of simulated groundwater flow in tight oil reservoirs and the theory of boundary layer adhesion,the reasons for the nonlinear flow of some tight rock samples are discussed.(4)In order to clarify the flow characteristics of single-phase liquids in complex connected micro-nanochannels,nuclear pore structure parameters of nonlinear flow samples were extracted using nuclear magnetic resonance technology and a corresponding pore network model was established.Based on the percolation theory and the micro-nanoscale fluid dynamics model,the single-phase liquid flow patterns in the network models with different pore sizes and wetting angles were studied.Finally,the single-phase liquids in the hydrodynanic smooth micro-nano channels and the complex connected micro/nano network models were determined.The linear flow mechanism.Through the above studies,the critical dimensions for the continuous fluid mechanics theory have been clarified,the mechanism of action between the fluid and the wall at the micro-and nanoscale scale has been revealed,and a simple and effective micro-nanoscale hydrodynamic model has been established,which enriches the micro-nanoscale hydrodynamics.The theory lays the foundation for the in-depth development of micro-nanoscale hydrodynamics. |
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