Study On The Temperature Overshooting Phenomenon During Micro/Nano Scale Heat Conduction Process

The traditional Fourier heat conduction law leads to infinite velocity of heat propagation, that is, if a sudden change of temperature is made at some point on the body, it will be felt instantly everywhere. However, in many nano scale heat conductions and transient heat conductions with high heat flux the characteristic time is normally less than the relaxation time of the heat conduction material. The heat does not transport by diffusion process but propagates in a finite speed in the form of waves. In that case, the temperature distribution in the heat conduction medium is different from that predicted by Fourier’s law. For example, if there is no heat source in the heat conduction medium, the temperature in the inner region may exceed the temperature at the boundary or the initial instant, which is called the temperature overshooting phenomenon. If the redundant heat induced by the temperature overshooting can not be appropriately managed, it may deteriorate or even damage the nano scale electronic devices. Therefore, the study of temperature overshooting phenomena occurring in nanoscale heat conduction is of great scientific significance and practical value. In this thesis, based on some typical non-Fourier heat conduction models, the temperature overshooting phenomenon in nano scale heat conduction process is systematically investigated and the occurring condition for the temperature overshooting is also established.Firstly, based on the Fourier law and the CV model the difference between the parabolic heat conduction equation and the hyperbolic heat conduction equation is illustrated. It is found that for the CV model heat propagates with the finite velocity in a wavelike way, and under some specific boundary conditions, the notable temperature overshooting phenomenon may occur. Meanwhile, the temperature overshooting phenomenon in a rectangular region is studied and is more visible than one-dimensional case under the same type of boundary condition.Then based on the dual-phase-lagging (DPL) heat conduction model, the influence of boundary conditions on the temperature overshooting is studied. By taking the heat conduction in a thin film as an instance, one dimensional DPL heat conduction equation is solved under different boundary conditions. It is found that when the temperature of one side jumps to a higher temperature while the temperature of the other side remains unchanged, the temperature overshooting cannot occur. If thermal perturbations are imposed on both boundaries of the film, the temperature overshooting phenomenon will be observed on certain condition. Furthermore, the overshooting amplitude will reach the maximum when the two thermal perturbations on both boundaries are identical. If the temperature on one boundary jumps to a high temperature while the other keeps adiabatic or natural convection condition, the temperature overshooting may occur.Since in many nanoscale heat conductions the influence of the size of the heat conduction medium on the heat conductivity is significant, the impact of the size effect on the temperature overshooting phenomenon is investigated based on an improved CV model in this thesis. It is found that the temperature overshooting occurs only when Kn>1.103. And the larger the Knudsen number, the more significant the temperature overshooting is.Finally, the lattice Boltzmann method is employed to study the temperature overshooting phenomenon for nanoscale heat conductions in thin films. The numerical calculation results show that the temperature overshooting can take place under the total phonon energy boundary condition.