微纳尺度传热问题的理论分析和格子Boltzmann数值模拟

发布时间：2018-05-23 19:10

本文选题：微纳尺度导热 + 超快速激光加热　；参考：《山东大学》2015年博士论文

【摘要】：超快速脉冲激光加热技术已被广泛应用于材料科学、纳米技术等诸多领域,而激光加热引起的纳米尺度的导热规律仍有待进一步探索,并成为该技术进一步发展的制约因素。许多微电子元件的尺寸已达到纳米级,为了设计其散热系统,必须深入研究微纳尺度导热的机理。对于微纳尺度导热问题,实验、理论和数值结果均表明暗含传播速度无限大假设的传统傅立叶定律不再适用。因此,探索微纳尺度导热规律具有重要的理论价值和应用价值。本文基于Cattaneo-Vernotte(CV)导热模型、双相滞(DPL)导热模型和体现尺度效应的改进的CV导热模型,应用解析方法对超快速激光加热引起的导热问题开展了系统的研究。并应用格子Boltzmann方法(LBM)数值模拟了超快速激光加热问题和微纳尺度热点引起的导热问题。本文首先基于傅立叶定律和CV导热模型,研究了超快速激光加热金薄膜引发的薄膜内部的导热问题,并将两个模型给出的结果进行了比较。研究结果表明,在CV导热模型中,热是以波动方式传输的,而不再是基于傅立叶定律的扩散传输方式,因此消除了热扰动传播速度无限大的缺陷,并得到了不同克努森数下“热波”在薄膜内部传播的无量纲速度。同时发现在绝热边界条件下,当系统达到稳定后,温度会随着克努森数的增加而升高。基于DPL导热模型对超快速激光加热金薄膜的一维导热问题进行了研究。结果表明,增大温度梯度迟滞时间与热流密度迟滞时间的比值会降低薄膜被激光加热一端的温度峰值,并缩短系统达到稳定状态的时间。基于DPL导热模型给出了在激光加热薄膜的导热过程中“热波”发生的必要条件。另外发现当温度梯度迟滞时间大于热流密度迟滞时间时,导热过程将不再发生热波现象,这一结论既符合本文的计算结果,又验证了Tang的结论。同时研究了在滑移边界条件下,表面调节系数对薄膜内温度分布的影响,研究结果表明,受加热表面的温度会随着表面调节系数的增加而降低。本文还基于DPL导热模型研究了不同克努森数下薄膜内部热流密度的分布情况,结果表明,当系统达到稳定状态时,热流密度的值随着克努森数的增加而增大。在微纳尺度导热系统中,导热系数与系统的特征长度紧密相关。因此本文基于体现尺度效应的改进的CV导热模型对超快速脉冲激光加热金薄膜的导热问题进行了研究。在与CV导热模型给出的结果的比较中发现,在改进的CV导热模型中热波的波峰并不出现在薄膜的内部,而是始终位于受加热边界。还发现两个模型所得无量纲速度值之间的大小取决于克努森数是否大于1.1027。在与DPL导热模型给出的结果进行比较时,发现两种模型所得到的温度分布存在较大差别,而且随着克努森数和DPL导热模型中的温度梯度迟滞时间的增大,两者的差别愈发明显。本文利用LBM数值模拟了激光加热硅薄膜的一维导热问题,结果表明,在过渡区由激光加热引起的薄膜内部的能量是以波动的形式进行传输的,且随着克努森数的增大,能量密度峰值变高。利用激光分别对薄膜的两侧进行加热时,发现由激光在薄膜两侧施加扰动引起的热波在薄膜内相遇时,会引发能量的剧烈增强。在与傅立叶定律和CV导热模型给出的结果的比较中,发现傅立叶定律不能展示能量的波动传输方式,且会严重低估薄膜内产生的能量密度峰值。CV导热模型虽然能够展示能量的波动传输形式和热波在相遇后的能量增强现象,但会低估能量增强的幅度。此外,本文还提出了通过控制激光作用于薄膜两侧的时间差,从而调节薄膜内能量最大值产生位置的方法,这对激光加热技术具有一定的指导意义。本文最后利用LBM研究了绝缘体上硅(SOI)晶体管的硅薄膜中纳米尺寸热点引发的导热问题。结果表明,在过渡区能量是以波动的形式进行传输的,并且边界条件对薄膜内能量的高低具有十分重要的影响。
[Abstract]:Ultra fast pulse laser heating technology has been widely used in materials science, nanotechnology and many other fields, and the thermal conductivity of nanoscale caused by laser heating remains to be further explored, and it has become a restriction factor for the further development of this technology. It is necessary to study the mechanism of micro nano scale heat conduction. For the micro and nanoscale heat conduction problem, the experimental, theoretical and numerical results show that the traditional Fu Liye's law with infinite propagation velocity is no longer applicable. Therefore, it is of great theoretical value and application value to explore the law of micro and nanoscale heat conduction. This paper is based on Cattaneo-Vernotte (CV). The heat conduction model, the dual phase hysteresis (DPL) heat conduction model and the improved CV heat conduction model, which reflect the scale effect, have been applied to the systematic study of the heat conduction problems caused by ultra fast laser heating, and the lattice Boltzmann method (LBM) is used to simulate the heat conduction problems caused by the ultra fast laser heating and the micro and nanoscale hot spots. In this paper, based on Fu Liye's law and the CV heat conduction model, the heat conduction in the film caused by a ultra fast laser heating gold film is studied. The results of the two models are compared. The results show that in the CV heat conduction model, the heat is transmitted in a wave mode, and is no longer a diffusion mode based on Fu Liye's law. Therefore, the infinite propagation velocity of thermal disturbance is eliminated, and the dimensionless velocity of the "hot wave" propagating in the film is obtained under different Knudsen numbers. At the same time, it is found that under the adiabatic boundary condition, when the system reaches stability, the temperature will rise with the increase of the Knudsen number. Based on the DPL heat conduction model, the ultra fast laser is heated to the gold thin. The one-dimensional heat conduction problem of the film has been studied. The results show that increasing the ratio of the hysteresis time of the temperature gradient and the delay time of the heat flux will reduce the temperature peak of the film being heated at the end of the laser and shorten the time of the system to reach the stable state. Based on the DPL heat conduction model, the heat wave in the heat conduction process of the excited light heating film is given. It is also found that the heat wave will no longer occur when the temperature gradient lag time is greater than the delay time of the heat flux. This conclusion is not only in accordance with the results of this paper, but also verifies the conclusion of Tang. At the same time, the influence of the surface adjustment coefficient on the temperature distribution in the film under the slip boundary condition is studied. The results show that the temperature of the heated surface decreases with the increase of the surface adjustment coefficient. In addition, based on the DPL heat conduction model, the distribution of heat flux in the thin films under different Knudsen numbers is studied. The results show that when the system reaches a stable state, the value of the heat flux increases with the increase of the number of Knudsen. In the heat conduction system, the thermal conductivity is closely related to the characteristic length of the system. Therefore, based on the improved CV heat conduction model which reflects the scale effect, this paper studies the heat conduction problem of the ultra fast pulse laser heating gold film. In comparison with the results obtained from the CV heat conduction model, it is found that the wave peak of the thermal wave in the improved CV heat conduction model is also found. It does not appear in the interior of the film, but always located at the heated boundary. It is also found that the size of the dimensionless velocity between the two models depends on whether the number of the 1.1027. is larger than the results given by the DPL heat conduction model, and it is found that the temperature distribution of the two models is very different, and with the Knudsen number. The difference between the two is more obvious with the increase of the temperature gradient delay time in the DPL heat conduction model. This paper uses the LBM numerical simulation to simulate the one-dimensional heat conduction problem of the laser heated silicon thin film. The results show that the energy in the thin film caused by laser heating is transmitted in a wave form in the transition zone, and with the increase of the Knudsen number, The peak of the energy density is higher. When the two sides of the film are heated by laser, it is found that the heat wave caused by the disturbance caused by the disturbance of the laser on both sides of the film will cause the intense enhancement of the energy. In comparison with the results given by Fu Liye's law and the CV heat conduction model, it is found that Fu Liye's law can not show the wave of energy. The dynamic transmission mode, and it will seriously underestimate the peak of the energy density in the thin film,.CV heat conduction model, although it can show the wave propagation form of energy and the energy enhancement after the heat wave at the meeting, but will underestimate the amplitude of the energy enhancement. In addition, this paper also proposes to adjust the time difference between the two sides of the film by controlling the excitation of the excitation light, thus adjusting the thin film. The method of producing the position of the maximum energy in the film has a certain guiding significance for the laser heating technology. In this paper, the heat conduction problem caused by the nano size hot spots in the silicon film on the silicon (SOI) transistor on the insulator is studied by LBM. The results show that the energy in the transition region is transmitted in the form of wave, and the boundary condition is the same. The energy level in the film has a very important influence.
【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TK124

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