Research On The Motion Characteristics Of Solid Particles In The Mushy Zone Of Solid-liquid Phase Transition

Solid-liquid phase change energy storage technology has the advantages of large heat storage per unit volume,small temperature fluctuation,small volume change,less pollution and good thermo-chemical stability.It has been widely used in building energy conservation,solar energy system,power system and military industry.Solid-liquid phase change materials store and release heat through phase transformation.The melting and solidification process mainly occurs in the mushy zone where solid and liquid coexist.Studying the motion characteristics and heat transfer characteristics of phase change particles in the mushy zone is conducive to mastering the mechanism of solid-liquid phase change and optimizing phase change energy storage technology.In this thesis,the numerical simulation method is used to study the heat transfer characteristics of particle movement and melting in the mushy zone.Based on the detailed analysis of the physical mechanism of phase change particle movement in gravity field,the migration and deformation of particle interface are tracked by arbitrary Lagrange Euler method,and the mathematical model of phase change particle movement and melting in the channel is established.The phase change and movement process of single particle and particles in the channel are simulated and solved by finite element method.The effects of the ratio of particle size to channel size,the initial position of particles in the channel,the main flow velocity in the channel and the arrangement of particles on the motion and heat transfer characteristics of phase change particles are analyzed.The results show that during the falling movement of phase change particles in the gravity field,vortices are formed on both sides and at the rear,the particle surface will melt unevenly,and gradually form an irregular shape with arc shape at one side and bulge at the other side.At the same time,the displacement of the center of mass causes the particles to rotate showing a complex motion form.The ratio of particle size to channel size,the initial position of particles in the channel and the main flow velocity in the channel have significant effects on particle motion and phase transition.The wider the channel is,the larger the particle offset is,the faster the moving speed is,the more irregular the boundary shape is,and the phase transition process is intensified.The initial position has a complex influence on the rotation and centroid offset of particles in the process of falling.The velocity of the main body in the channel affects the moving speed and heat transfer of the falling particles.When the main body velocity is down,the eddy current on both sides of the particle decreases and the moving speed increases.When the main body speed is up,the falling movement of particles is hindered.The phase change,motion and heat transfer of multiple particles are more complex,and the influence of particles arrangement is the most significant.In the falling process of vertically arranged double particles,there are phenomena such as drag and collision.The lower particles will hinder the movement and heat transfer process of the upper particles,resulting in the difference of phase velocity between the two particles.The smaller the channel width,the greater the interference of the two particles,and the falling velocity is significantly different.Three particles and multiple particles will collide and drag each other in the falling process,which makes the particles have complex motion trajectories in the channel,thus affecting the phase transition process of the particles.