Research On Flow And Heat Transfer Of Two-Phase Flow Based On Lattice Boltzmann Method

Energy demand has been increased dramatically since the 21st century,but the current energy extraction technology and the lack of energy utilization rate cause serious energy consumption and other problems are still prominent.The study of multiphase flow and heat transfer is of great significance in both theory and practice,however,there are still numerous outstanding problems to be solved in this field of research.The lattice Boltzmann method,which has been developed in the past three decades for the investigation of fluid flow and heat transfer,has the advantages of clear physical meaning and inherent parallelism compared with traditional numerical simulation methods.In this thesis,based on the lattice Boltzmann method,a two-phase flow separation model and a droplet injection model are established,and the two-phase flow and heat transfer are studied numerically at the mesoscopic level.Through this thesis,it is expected to deepen scholars’ understanding of the direction of two-phase flow and heat transfer as well as to provide some theoretical references for engineering applications and energy extraction.The main works done in this thesis are as follows:(1)In this thesis,a lattice Boltzmann model based on two-phase separation in temperature field is established,and using this model,two-phase separation under temperature field,as well as its fluid flow and heat transfer characteristics,are examined.The behavioral performance of the three processes of collision,interface opening,and fusion experienced by droplet formation is analyzed in detail.Through the data analysis,it is concluded that the velocity and temperature on the droplet liquid film are symmetrical with respect to the central position of the liquid film.In addition,the droplet velocity is also symmetrical about the center of the droplet circle,which provides a theoretical basis for the droplet to maintain stability.The temperature distribution formula inside the square cavity is proposed by varying the temperature difference between the wall surfaces,which is in high consistent with the simulated value with a maximum error of 10.1%.(2)The two-phase separation rate was further improved by adding the lid-driven effect to the two-phase separation model.It is the first time to divide the droplet collision into primary phase,ultimate phase,and stable phase according to the axis length,and the oscillatory deformation characteristics of the droplet deformation process are studied.The tendency of gradual decrease of internal velocity variation during droplet collision was found by the velocity profile.Two vortices with opposite directions will be formed in the square cavity under the action of the lid-driven,and there will be an abrupt variation of velocity and temperature in the liquid film region.The study in this paper makes a meaningful supplement to the two-phase separation.(3)To improve fuel utilization,a droplet injection model was developed.The two-phase flow is investigated by modifying the model to atomize the droplets into small droplets,which increases the specific surface area of the droplets and boosts the energy utilization rate.The study captures the rupture process of droplets,analyzes the morphological changes of droplets and the influencing factors,and investigates the oscillatory deformation in the process of droplet evolution.According to the variation of gas-liquid two-phase flow velocity,the droplet injection is divided into three parts:uniform zone,non-uniform zone,and jet zone,emphasizing on the relationship between droplet size and two-phase flow velocity in the uniform zone.On the other hand,the droplet vaporization length and liquid spacing were compared in accordance with different gas-liquid two-phase velocities,and the relationship between the formation angle and droplet diameter was evaluated by fitting the equation of liquid spacing and droplet diameter through the data analysis.