发散微纳通道内的流场和温度场研究
Flow and Thermal Fields Investigation in Divergent Micro/Nano Channels
摘要：
本论文主要研究氮气在微纳通道中的流动。采用直接模拟蒙特卡罗（DSMC）方法对流动进行了研究。简化伯努利试验（SBT）碰撞计划已被用来减少计算成本和所需的计算机资源量。本文研究了在滑移晚期和转捩早期不同努森数条件下，不同发散角对流场和热场的影响。对于具有均匀恒定壁温的微米和纳米通道，入口与出口压力比已被设置为2.5。通过对数值结果的分析，没有发现由于壁面滑移而导致的流动分离，这与连续区的流动行为不同。结果表明，粘性组分对总压降和流动特性有较大的贡献。观察到，对于低发散角，压力的影响主导剪切应力和发散角的影响，并导致流动沿通道加速，而通过增加发散角，从而增加流动膨胀的影响，流动沿通道减速。通过通道的质量流率通过增大发散角而增大。冷到热的传热已被观察到在发散的微米和纳米通道。为了研究发散微纳米通道中的热行为，将结果与从Boltzmann方程导出的弱非线性本构律进行了比较。
英文摘要：
The present work is related to the study of the nitrogen gas flow through diverging micro and nano-channels. The direct simulation Monte-Carlo (DSMC) method has been used to study the flow. The Simplified Bernoulli Trials (SBT) collision scheme has been employed to reduce the computational costs and required amounts of the computer resources. The effects of various divergence angles on flow and thermal fields have been studied for different Knudsen numbers in late-slip and early-transition regimes. The inlet-to-outlet pressure ratio has been set to 2.5 for micro and nano-channels with a uniform constant wall temperature. By analyzing the numerical results no flow separation has been found due to slip at the wall which is different than flow behavior in continuum regime. The results indicate that the viscous component has a relatively large contribution to the overall pressure drop and flow behavior. It observed that for low divergence angles the effects of pressure forces dominate the effects of shear stress and divergence angle and cause the flow to accelerate along the channel while by increasing the divergence angle and therefore the effects of flow expansion, the flow decelerates along the channel. The mass flow rate through channel increases by increasing the divergence angle. Cold-to-hot heat transfer has been observed in diverging micro and nano-channels. In order to investigate the thermal behavior in diverging micro and nano-channels, the results have been compared to weakly non-linear constitutive laws derived from Boltzmann's equation.
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