Study On Contact Angle By Chemical-Potential Lattice Boltzmann Method

Multiphase flow is common in industrial production and daily life.It mainly studies multiphase fluid motion with more than two different phases.In computational fluid dynamics,the use of numerical simulation technology has evolved into a reliable cross discipline.Its high efficiency,accuracy,and expansibility have also been generally confirmed.It has been widely used in multiphase flow studies.In the past three decades,the lattice Boltzmann method has become a new method of computational fluid dynamics.It originated from the theory of molecular dynamics and lattice gas automata.It uses mesoscopic kinetic equations to simulate and study macroscopic fluid behavior with macroscopic and microcosmic properties.The advantages of the method.This method has made outstanding contributions in the field of multiphase flow.The advantages are as follows: 1.The algorithm is simpler than the traditional model,and it does not need to solve the complex macroscopic Navier-Stokes equations,but only needs to solve the lattice Boltzmann equation;2 The complex geometric boundary is effectively processed;3.Because the evolution of LBM has locality,it is very suitable for high-performance parallel computing.In this paper,the multiphase flow model based on the chemical potential lattice Bolzmann method is used to simulate the contact angle phenomenon,and the micro contact angle morphology,contact angle measurement and contact angle movement are analyzed in depth.Chemical potential,as an important thermodynamic strength,represents the partial molar Gibbs free energy under constant pressure,which is of great significance in dealing with the problems of phase change and chemical change.In this paper,the non-ideal force is calculated directly from the chemical potential,and then the non-ideal force is applied to the lattice Bolzmann equation.This avoids the calculation of the pressure tensor and its divergence,and therefore has a higher numerical calculation efficiency;also from the free energy density.The function calculates several common chemical equations of the fluid state equation.Combined with the chemical potential boundary conditions for the study of the wettability of the solid surface,the measured contact angle can be adjusted linearly by the surface chemical potential.The contact angle is a fundamental feature in the problems of surface wetting,capillary phenomena and moving contact lines.The contact angle is the result of gas-liquid-solidthree-phase interaction.Although the contact angle phenomenon can be effectively simulated in numerical calculations,the contact angle cannot be accurately measured in real time.In this paper,a geometric method is designed to measure the contact angle in real time.Under the condition of neglecting the gravity,the calculation result of this method is consistent with the theoretical expectation of the spherical cap model and is not affected by the size of the droplet;under the consideration of gravity,although the droplet is obviously deformed,the measured microscopic contact is obtained.The angle remains unchanged,consistent with the theoretical expectations.When the substrate is tilted,the droplets slide over hydrophilic and hydrophobic bands with different chemical potentials.Experiments show that the progressive increase of the advancing angle is accompanied by a gradual decrease in the receding angle,and the advancing and receding angles are not synchronized,resulting in fluctuations in the contact angle.status.In the dynamic contact angle hysteresis,there is a slight phase difference between the advancing angle and the receding angle,resulting in a high-order undulation image when the droplets slide,and the method can measure the contact angle in real time.Based on theoretical and numerical simulations,this paper verifies the main characteristics and advantages of the multiphase flow model based on chemical potentials,respectively:1.The establishment of the chemical potential multi-phase flow model,the direct calculation of non-ideal forces using chemical potentials,and the application of non-ideal forces to the lattice Boltzmann equation.It is more efficient in computational time and space because he avoids calculating pressure tensors and their divergence.2.The chemical potential multiphase flow model has a solid theoretical basis,a clear concept,and high computational efficiency.In this paper,the chemical potentials corresponding to the most commonly used fluid state equations are selected.The calculated experimental values are compared with the solutions of Maxwell's iso-area structures.The numerical results verify that the model not only has thermodynamic consistency and Galileo invariance,but also It also has good stability and high precision.3.Based on the comparison of chemical potential-based multiphase flow model and spherical-crown model simulation data,it is found that the simulated data is highly consistent with the data of the benchmark spherical-crown model,which provides a solid foundation for real-time measurement of contact angles.Since the chemical potential can linearly regulate the degree of wettability,the contact angle was measured under a mesoscopic structure and it was found that the chemical potential model calculation results have higher accuracy and higher efficiency.4.Preliminary application of the Boltzmann multiphase flow model based on the chemicalpotential lattice,measurement of contact angles on chemically heterogeneous surfaces.For a given droplet,in the absence of gravity,it is in perfect agreement with the spherical cap model,indicating that the chemical potential multiphase model can accurately measure the contact angle;under gravity,we simulate the droplets with different radii,and the sphere cap The model was numerically compared and it was found that the contact angle was almost constant based on the chemical potential multiphase model.A large number of simulation experiments were performed on static contact angle hysteresis and dynamic contact angle hysteresis,respectively,and rigorous analysis and research were performed using numerical simulation.By using the chemical potential to linearly adjust the wettability of the droplet surface,the advancing and receding angles can be accurately calculated.For the dynamic contact angle,the trajectory of dynamic contact angle and the law of hysteresis fluctuation are also studied.