Molecular Simulation Of Transfer Behaviors Of Fluids Controlled By Surface Wettability In Nano/microscopic

The interfacial effects at nano/micro scale can cause specific phenomena such as properties changed of fluids.It brings many different transfer phenomena from macroscopic which brings opportunities and challenges to the development of modern chemical engineering.Fluids in nano/micro scales exhibit some special transfer behaviors,such as directional transport,wettability conversion,ultra-fast water transport,etc.,which can realize nano/micro-flow control,seawater desalination,efficient heat transfer and other specific applications.However,the experimental observation of nano/microscale fluid flow process is still limited,and the regulation mechanism and theoretical description of nano/microscale transfer process are also left unexplored.In this paper,the molecular simulation methods are used to investigate several common transfer phenomena in chemical engineering,including dynamic wetting,droplet dispersion,mass transport and convective heat transfer in nanochannels.The regulation mechanism of solid-liquid interaction and surface wettability on the nanoconfined fluid transfer processes were studied,which provided theoretical support for the design of new process intensification methods and nanoscale reactors.The main work and innovation of this paper are as follows:1.The study of dynamic wetting behavior of nanodroplets on nanopillared surfaces.The influence of surface nanostructure and wettability on the motion and evolution of nanodroplet were revealed.The similarities and differences between the Cassie state and Wenzel state on the rough surface were found.The dynamic advancing contact angle and receding contact angle are positively and negatively correlated with the velocity of contact line,respectively.The quasi-static contact angle was proposed to describe the wettability of rough surfaces,and a dynamic contact angle model was established.It was revealed that the energy dissipation on the dynamic contact line includes viscous dissipation and frictional dissipation,both of which determine the droplet morphology.It was found that the energy dissipation of Wenzel state is greater than that of Cassie state,and the energy dissipation forms of advancing and receding contact lines are different.The research results have important theoretical significance for the design of functional surfaces.2.The effects of surface wettability coupling fluid properties on the behaviors of droplet impact on cylindrical surfaces were investigated systematically.It was found that the increase of surface wettability inhibits droplet spread at high impact velocities,while the increase of surface wettability promotes droplet spread at low impact velocity.These results broaden the monotonic relationship between surface wettability and maximum spreading length found in previous studies.The machine learning（ML）models were established to predict sufficient and necessary conditions for impact behaviors.Compared with traditional parameter fitting models,ML models have the advantages of high reliability and simple form.The comprehensive understanding and prediction of droplet dynamic behaviors play an important role in the design of process intensification equipment.3.The effects of interfacial atomic interactions on mass transport in a confined space were studied in the case of using the COF membrane for desalination.The desalting performance of COF membranes with adjusted pore sizes and layers were studied.The permeability and salt rejection of COF_3-2membrane are 35.7 L/cm²/day/MPa and 96.7%,respectively.From the aspect of overall performance,the permeability of COF_3-2membrane is more than two orders of magnitude higher than commercial reverse osmosis membranes.It was found that the pore structure of COF membranes affected the water structure around the nanopore.The continuous hydrogen bond network appearing on both sides of the COF membrane and the hydrogen bond formed between water molecules and nitrogen atoms in the COF membranes are the key factors for the water flux.According to our simulations,the energy barrier of water through the COF membrane pore is much lower than that of ions,thus high salt rejection and water flux can be obtained.It was proved that the COF membrane has great application prospect in seawater desalination and has important reference value for experimental synthesis and design of super thin membranes in the future.4.The momentum and heat transfer of fluid flow in nanochannels were studied by taking heat dissipation in nanochip as an example.The mechanism of wettability and channel size on convective heat transfer behavior in nanochannels was revealed.The spatial limitations introduced by the nanochannel and the solid-liquid interaction change the structure and diffusion properties of the fluid,especially the near-wall fluid.The components of energy dissipation in the heat transfer process are determined,including friction dissipation and viscous dissipation.It was found that the energy dissipation becomes more obvious with decreasing the channel height.Thus,simply reducing the channel size to enhance the heat transfer effect is not desirable.These results offer new insights into convective heat transfer in nanochannels and provide theoretical guidance for the design of nanofluidics.In summary,the influence of surface wettability and space confinement effect on fluid transfer behavior and its regulation mechanism were explored.The coupling mechanisms of fluid properties and surface properties with fluid flow behaviors,flow with mass transfer and flow with heat transfer were revealed.Transfer models including surface properties（nano/microstructure,wettability,etc.）and characteristics of confined space were established.The macroscopic transfer equation is extended to nano/microscale,and the transfer mechanism in chemical engineering is illustrated from the molecular scale.The results expanded the nanoscale transfer phenomenon and theory.It is of great significance to the development of process intensification methods and the design of nano/micro reactors.