School of Mechanical Engineering, Kalinga Institute of Industrial Technology, Bhubaneswar 751024, India.
Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, India.
Phys Rev E. 2018 Apr;97(4-1):043302. doi: 10.1103/PhysRevE.97.043302.
Spatiotemporal thermal response and characteristics of net entropy production rate of a gold nanosphere (radius: 50-200 nm), subjected to a short-pulse, femtosecond laser is reported. In order to correctly illustrate the temperature history of laser-metal interaction(s) at picoseconds transient with a comprehensive single temperature definition in macroscale and to further understand how the thermophysical response of the single-phase lag (SPL) and dual-phase lag (DPL) frameworks (with various lag-ratios') differs, governing energy equations derived from these benchmark non-Fourier frameworks are numerically solved and thermodynamic assessment under both the classical irreversible thermodynamics (CIT) as well as extended irreversible thermodynamics (EIT) frameworks is subsequently carried out. Under the frameworks of SPL and DPL with small lag ratio, thermophysical anomalies such as temperature overshooting characterized by adverse temperature gradient is observed to violate the local thermodynamic equilibrium (LTE) hypothesis. The EIT framework, however, justifies the compatibility of overshooting of temperature with the second law of thermodynamics under a nonequilibrium paradigm. The DPL framework with higher lag ratio was however observed to remain free from temperature overshooting and finds suitable consistency with LTE hypothesis. In order to solve the dimensional non-Fourier governing energy equation with volumetric laser-irradiation source term(s), the lattice Boltzmann method (LBM) is extended and a three-time level, fully implicit, second order accurate finite difference method (FDM) is illustrated. For all situations under observation, the LBM scheme is featured to be computationally superior to remaining FDM schemes. With detailed prediction of maximum temperature rise and the corresponding peaking time by all the numerical schemes, effects of the change of radius of the gold nanosphere, the magnitude of fluence of laser, and laser irradiation with multiple pulses on thermal energy transport and lagging behavior (if any) are further elucidated at different radial locations of the gold nanosphere. Last, efforts are further made to address the thermophysical characteristics when effective thermal conductivity (with temporal and size effects) is considered instead of the usual bulk thermal conductivity.
报道了金纳米球（半径：50-200nm）在短脉冲飞秒激光作用下的时空热响应和净熵产生率的特征。为了正确说明皮秒瞬态激光-金属相互作用的温度历史，提出了一种在宏观上用综合单一温度定义来描述的方法，并进一步了解单相滞后（SPL）和双相滞后（DPL）框架（具有不同的滞后比）的热物理响应有何不同，从这些基准非傅里叶框架导出的控制能量方程被数值求解，并在经典不可逆热力学（CIT）和扩展不可逆热力学（EIT）框架下进行热力学评估。在小滞后比的 SPL 和 DPL 框架下，观察到温度过冲等热物理异常，其特征是存在不利的温度梯度，违反了局部热力学平衡（LTE）假设。然而，EIT 框架证明了在非平衡范式下，温度过冲与热力学第二定律的兼容性。然而，观察到具有较高滞后比的 DPL 框架不受温度过冲的影响，并与 LTE 假设保持一致。为了解决具有体积激光辐照源项的非傅里叶控制能量方程的维度问题，扩展了格子玻尔兹曼方法（LBM），并说明了一种三时间级、完全隐式、二阶精度的有限差分法（FDM）。在所观察到的所有情况下，LBM 方案在计算上优于剩余的 FDM 方案。通过所有数值方案详细预测最大温升和相应的峰值时间，进一步阐明了在金纳米球不同径向位置处，金纳米球半径的变化、激光强度的大小以及多脉冲激光照射对热能量输运和滞后行为（如果存在）的影响。最后，进一步努力研究了在考虑有效热导率（具有时间和尺寸效应）而不是通常的体热导率时的热物理特性。
