Study On Molecular Dynamics Of Bubble Nucleation In Rapid Transient Explosive Boiling

Explosive boiling is a hypernormal boiling phenomena caused by a transient high heat flux. It is widely applied in many fields such as ink jet print, metallurgy and transportation of natural gas. There are many special characteristics of explosive boiling:a high superheated degree, explosive bubble nucleation and growth, a large amount of very small sized bubbles, shock wave in an extreme condition. Classical thermodynamics cannot be used to explain this phenomenon. This is because explosive boiling occurs in an nm spatial scale and ps temporal scale, which is a combination of micro scale heat transfer and complicated phase change. It is a new challenge to the classical theory and experimental technology due to the hypernormal phenomenon in the process of heat and mass transfer in explosive boiling.Molecular dynamics simulation is carried out for the bubble nucleation of liquid nitrogen in explosive boiling. The heat is transferred into the simulation system by rescaling the velocity of the molecules. The results indicate that the initial equilibrium temperature of liquid and molecular cluster size affect the energy conversion in the process of bubble nucleation. The potential energy of the system violently varies at the beginning of the bubble nucleation, and then varies around a fixed value. At the end of bubble nucleation, the potential energy of the system slowly increases. In the bubble nucleation of explosive boiling, the lower the initial equilibrium temperature, the larger the size of the molecular cluster, and the more the heat transferred into the system of the simulation cell can increase the potential energy in a larger range.Molecular dynamics simulation is carried out for the bubble nucleation of water and liquid nitrogen in explosive boiling. The heat is transferred into the simulation system by rescaling the velocity of the molecules. When heat is added into the molecular cluster, liquid initial equilibrium temperature and molecular cluster size can affect the energy conversion in the process of bubble nucleation. The potential energy of the system violently varies at the beginning of the bubble nucleation, and then varies around a fixed value. At the end of the bubble nucleation, the potential energy of the system slowly increases. In the process of bubble nucleation of explosive boiling, the lower initial equilibrium temperature leads to the bigger size of the molecular cluster. With more heat added into the system of the simulation cell, the potential energy varies in a larger range.A bubble nucleation on solid surface in explosive boiling is simulated by the molecular dynamics method. Liquid water on a solid surface is heated until bubble nucleated. Temperature and pressure of water system is calculated in the process of bubble nucleation. The volume of the bubble void and the diameters of the void are calculated. The bubble growth rate is determined by doing statistics on the bubble diameters. The nucleation rate of the simulation and the radial distribution function in the process of nucleation are analyzed. The radius of the bubble grows rapidly at the beginning of the nucleation.Molecular dynamics simulations are performed to study the thermal and thermalmechanical phenomena of ultra-high heat flux conduction induced by laser heating in thin Si films. The semi-infinite Si films in the depth 32.3nm,40.4nm, 48.4nm,60.5nm,75.6nm of the heat flux direction are simulated to study the conduction process of heat flux. A distribution of internal heat source in the depth of the thin films is applied to simulate the absorption of the laser in films. Temperature distribution, stress distribution and the evolution of the displacement in the Si films are calculated. The thermal waves are observed according to the distribution of temperature in heat flux direction. The average temperature of the simulated Si films increases linearly, while the average stress shows periodic oscillations. The strain in the heat flux direction in different depth of the films shows the same trend as the average stress throughout the film. The net heat flux shows the same trend as the stress in different depth of the Si films in the direction of heat flux, which shows the close relationship between the stress and the net flux in the Si films in the process of laser heating.