Theories And Applications Of Lattice Boltzmann Method To Bubble Growth And Multiphase Flow

Accompanied by the process of bubble nucleation, growth and detachment, the phenomenology of convective boiling and microscale transmission were presented. So it is important significance to investigate this process (bubble dynamics) in nuclear energy, aerospace, material technology fields and energy, power, petroleum, chemical, metallurgical, and other industry applications. Moreover, research on bubble dynamics is an intersectional fundamental study related to several fields, such as thermodynamics, heat transfer, and fluid mechanics and so on, and is of great science interest and engineering value. There are a number of complicated scientific issues in bubble dynamics, for example, the motion and growth of a rising bubble through a uniformly superheat liquid, bubble attaching, growing on and departing from a heated wall. At the present, our understandings and studies on these issues are far from being enough. This is because it is quit difficult to study with conventional theoretical analysis, field simulation and experimental investigation. Thus, some novel ideals of research should be developed.Considering the distinguished characters to deal with significant microscale interaction of the lattice Boltzmann method, which is a mesoscopic method, this dissertation implements numerical simulation for the liquid-vapor phase transition based on lattice Boltzmann method and investigates the scientific issues involved in depth. This dissertation consists of two parts: extensions of basic theory of the multiphase lattice Boltzmann method and numerical studies of bubble growth and multiphase flow. Extensions of the theory of the multiphase lattice Boltzmann method:?A new multicomponent multiphase lattice Boltzmann model, which is constructed a new equilibrium distribution function satisfied with D2Q9 model and chosen a new Green'function, is established a new high efficiency model. In this new model, the external force and interaction force between the solid wall and fluid could be considered. Considering mass exchange process, a new multicomponent multiphase lattice Boltzmann phase transition model, which incorporates into the phase transition equations, is established to describe homogeneous liquid-vapor phase transition.?A new single component multiphase lattice Boltzmann model (Improved Model One),which is based on SC model and Zhang model, is established to describe isothermal liquid-vapor phase transition. In this new model, a new method, which is proposed to calculate body force by using equation of state, is avoided implement of effective mass and its gradient. Moreover, the velocities are revised by using body force in this new model.?A new single component multiphase lattice Boltzmann model (Improved Model Two or Exact Difference Lattice Boltzmann Model), which is based on Zhang model and Exact Difference Method, is established to describe isothermal liquid-vapor phase transition. In this new model, the definition of interparticle potential which is describe the process of phase transition proposed by Zhang, and the calculation method of the body force which is used Exact Difference Method proposed by Kupershtokh. In addition, the velocities are revised by using body force in this new model.?A new single component multiphase lattice Boltzmann model, which is based on Exact Difference Method and heat transfer model proposed by Inamuro, is established to describe the liquid-vapor heterogeneous phase transition process. Whereafter, the multiscale expansion is adopted to derive the macroscopic hydrodynamic equations for this new model, and it is found that the energy equation deduced from this new model is consistent with the macroscopic entropy balance equation.Numerical studies of bubble growth and multiphase flow:?To validate the improved multicomponent multiphase lattice Boltzmann model, the relationships between difference pressure and radius for different viscosity ratios of the droplet, layered multiphase flow and relative permeabilities are simulated by this improved model. The wettability, which is related to the interaction strength coefficient between the solid wall and fluid, is explored to use this improved model. The dependence of the droplet sliding, fracturing and detaching on the wall on various contact angles, Bond numbers are investigated to use this improved model.?The condensation and vaporization are simulated by using the multicomponent multiphase lattice Boltzmann phase transition model. From these simulation results, it is found that the relationships between the volume fractions of vapor phase vs. evolution time and the liquid/vapor phase densities vs. evolution time are obtained. Compared with previous results, the present results are more closed to analytical results, and then the liquid/vapor phase masses vs. evolution time are investaged. It is found that these simulation results are good agreement with analytical soluations. Whereover, the different phase transition velocities can be obtained by changing the superheat?q . Finally, it is investaged that pool boiling and boiling flow in a vertical pipe are changed with different gravities, and pool boiling and boiling flow in a horizontal pipe are changed with different horizontal accelerates by using this new model.?In order to compare the Improved Model One with the SC and Zhang models, the van der Waals gas phase transition process was simulated by using above mentioned models, respectively. It is found that the Improved Model One makes same improvements of SC and Zhang models. Wheveafter, ammonia and water phase transition process were implemented by using Improved Model One with different equations of state. It is found that these simulation results are closed to their corresponding experimental data with Peng-Robinson equation of state. To investigate the interfacial property at the mesoscale level, the free energy functions were incorporated into the Improved Model One, and then mesoscopic interparticle potentials, equilibrium and nonequilibrium thermodynamic property parameters are investigated. It is found that all these parameters are obeyed irreversible thermodynamics.?Ammonia and water phase transition process were implemented by using Improved Model Two with different equations of state. From these simulation results, it is found that Improved Model Two makes a great improvement with Improved Model One about temperature range and the maximum density ratio. So, the mass density profiles across the interface, relationships between difference pressure and radius of the bubble (droplet), surface tensions of water and ammonia, metastable equilibrium and unstable equilibrium of water at a certain temperature, the conditions of bubble (droplet) formation in the isothermal phase transition process, the conditions of droplets coalescence and the relationships between liquid bridge and evolution time are all investigated to use Improved Model Two. From these simulation results, the present results of surface tension are good agreement with experiment data, and the relationships are satisfied with theoretical relationships verified by experiment.?Firstly, the relationship between interaction strength coefficient and static contact angle is investigated by using Improved Model Two. The domain size effect of bubble growth process is explored to use the heterogeneous phase transition model in pool boiling. It is found that when the bubble diameter did not exceed the half of the horizontal distance, the domain size effect become negligible. Moreover, the effects of gravity and static contact angle to the bubble growth process are investigated in pool boiling. Secondly, the effect of horizontal acceleration to the bubble growth and detachment is explored in boiling flow. Finally, the effect of the interaction strength coefficient between the solid wall and fluid to the bubble nucleation process is investaged in a pit. According to these simulation results, the process of bubble nucleation, growth and detachment are reproduced in detail, and then phase transition, bubble formation and other physical driving mechanism are analysised. It is apparent that these simulation results are in good agreement with experimental data.