A new iterative wall heat flux specifying technique in DSMC for heating/cooling simulations of MEMS/NEMS
A new iterative wall heat flux specifying technique in DSMC for heating/cooling simulations of MEMS/NEMS
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DOI：
10.1016/j.ijthermalsci.2012.04.002
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发表时间：
2012-09-01
影响因子：
4.5
通讯作者：
Stefanov, Stefan
中科院分区：
文献类型：
--
作者：
Akhlaghi, Hassan;Roohi, Ehsan;Stefanov, Stefan
具有特定壁面热流的微/纳几何结构在电子冷却和微/纳流体传感器中广泛遇到。在本研究中，我们引入了一种新的迭代技术施加所需的（正/负）壁热流边界条件的DSMC方法，可以用于模拟微/纳米机电系统（MEMS/NEMS）与给定的热能交换。在所提出的算法中，我们使用的计算和期望的壁热流率之间的无量纲差异，以提高迭代壁温的初始估计。松弛因子用于控制壁温值的校正。不同的数值参数，如每个细胞的模拟粒子数和松弛因子的精度，性能和鲁棒性的迭代技术的影响进行了研究。我们通过分析稀薄压力驱动的微/纳米通道流中的加热和冷却过程来研究我们的迭代技术。观察到一些独特的行为。例如，观察到与加热过程相反，微/纳米通道壁的冷却导致密度场的小变化。冷却过程中的上游热蠕变效应使速度滑移减小，但努森数沿通道沿着增大。此外，冷却过程改变了压力分布的曲率，使其低于线性不可压缩的。对于这里考虑的情况下，我们的研究结果表明，流动冷却增加通过通道的质量流率，反之亦然。研究了壁面换热对二维微纳空腔流动的流体力学和热行为的影响。(C)2012年Elsevier Masson SAS。All rights reserved.
Micro/nano geometries with specified wall heat flux are widely encountered in electronic cooling and micro-/nano-fluidic sensors. In the present study we introduce a new iterative technique to impose a desired (positive/negative) wall heat flux boundary condition in the DSMC method that can be useful for simulation of Micro/Nano electro-mechanical systems (MEMS/NEMS) with given heat energy exchange. In the proposed algorithm we use the non-dimensional difference between computed and desired wall heat flux rates to improve iteratively an initial estimate of the wall temperature. A relaxation factor is applied to control the correction of wall temperature values. Effects of different numerical parameters such as number of simulator particles per cell and relaxation factor on the accuracy, performance and robustness of the iterative technique are investigated. We examine our iterative technique by analyzing heating and cooling processes in rarefied pressure-driven micro/nanoscale channel flows. Some unique behaviors are observed. For example, it is observed that contrary to the heating process, the cooling of micro/nano channel walls results in small variations in the density field. The upstream thermal creep effects in the cooling process decrease the velocity slip although the Knudsen number increases along the channel. Additionally, the cooling process changes the curvature of the pressure distribution making it below the linear incompressible one. For the cases considered here, our results indicate that flow cooling increases the mass flow rate through the channel, and vice versa. We also investigate the effects of wall heat transfer on the hydrodynamics and thermal behaviors of the 2-D micro/nano cavity flow. (C) 2012 Elsevier Masson SAS. All rights reserved.