Numerical Simulation Of Three-dimensional Ultrafast Laser-induced Heat Transfer In Nano

Ultrafast laser induced nanomaterials is a very complex thermal conductivity process,and its results are not only affected by the physical properties of the laser,but also by the physical properties of the material.The size of nanofilms is often on the order of nanometres,and their size effect has a significant impact on the heat transfer characteristics of ultrafast thermal conductivity problems in tiny spaces.Fourier’s law can well describe macroscopic thermal conductivity problems,but it implies the assumption of infinite heat flow propagation speed,which no longer holds true when the heating time is extremely short when ultrafast laser induces nanomaterials.This article uses the Lattice Boltzmann Method(LBM)to study the heat transfer process of three-dimensional ultrafast laser induced nano thin film,exploring the changes in the three-dimensional temperature field inside the film at different times and the heat transfer inside the film.In this thesis,the Boltzmann Transport Equation(BTE)is used to describe the ultrafast laser-induced heat transfer in nanofilms,and the LBM method is used to solve the BTE equation,and its control equation is solved to obtain the three-dimensional control equation.Process the boundary conditions to obtain the mirror reflection boundary conditions for the three-dimensional heat conduction problem.Secondly,the BTE transport equation was used to investigate the problem of ultra fast heat conduction in small space.The results indicate that heat is transmitted in the form of thermal waves within the film,not in the diffusion mode of Fourier’s law;The heat transfer characteristics of thin films vary in the direction of laser irradiation and the tangential direction of laser irradiation,with more drastic changes in the direction of laser irradiation,demonstrating the differences in heat transfer within the film.The heat transfer characteristics of the film under different Knudsen number was investigated.The results show that the larger the Knudsen number is,the more obvious the thermal response in the film is,the shorter the time it takes for the film to reach the steady state,and the higher the internal temperature of the film when it is stable.Once again,the results of the three-dimensional thermal conductivity problem obtained using LBM were compared and analyzed with the results of the two-dimensional thermal conductivity problem obtained using LBM method,exploring the influence of spatial dimensions on the internal heat transfer characteristics of thin film.The results indicate that there are significant differences between the 3D and 2D simulation results,with the temperature of the 3D result being lower than that of the 2D result;At the beginning,the difference between the two is relatively small,and gradually increases as depth and time increase.The numerical simulation results obtained using the LBM are compared with the analytical results obtained using the CV thermal conductivity model and the Dual Phase Model(DPL)non-Fourier thermal conductivity model.The results showed that the LBM,CV thermal conductivity models,and DPL thermal conductivity models obtained very similar results,but as time increased,the three results began to show certain differences.Specifically,the thermal wave amplitude of the CV thermal conductivity model is relatively large and obvious;the thermal response of LBM results is faster and the time required to reach steady-state is shorter.Finally,based on the LBM method,the influence of laser heat sources on the nano film was investigated,and the influence of energy intersection on the internal heat transfer characteristics of the film,as well as the influence on the internal temperature field of the film,was explored.The results indicate that the energy convergence will cause the internal temperature of the film to reach a higher temperature,generating a higher temperature thermal wave,and the time taken for the film to reach steady state is shorter under the heat sources on both sides.When reaching steady state,the temperature inside the film is higher.And the difference between the two heat sources on both sides and the single heat source is not simply a superposition of two single heat sources.Due to the size effect,the internal heat of the film can be rapidly transmitted.When the two heat sources are on both sides,the internal temperature of the film is higher than the temperature of the single heat source and lower than the sum of the two single heat source temperatures.With the increase of the Knudsen number,the thermal response strain in the film is faster,and the film reaches a steady state faster.This is because when there are multiple heat sources,the heat sources on both sides of the film will produce energy convergence,which will change the temperature field inside the film.The temperature inside the film is higher,and the heat transfer rate is faster.In this paper,we have studied the unilateral laser heat source induced nanofilms and bilateral laser heat source induced nanofilms,and explored the changes in the internal temperature field of the films and the influencing factors,in order to achieve more accurate regulation of the internal temperature of the films by controlling various influencing factors.