使用弹性聚合物在二维蛇形微通道中增强传热
Enhanced heat transfer in a 2D serpentine micro-channel using elastic polymers
AI总结：
本研究通过Rheotool模拟Oldroyd-B流体在二维蛇形微通道中的流动，揭示了弹性湍流条件下基于Weissenberg数的三个传热与摩擦系数变化区域，发现弹性不稳定性显著增强了传热效率。
摘要：
在弹性力存在的情况下，即使稀薄的聚合物悬浮液也能表现出不稳定的流动波动，即使粘性力在趋于零的低雷诺数（Re）下主导惯性力。这种现象被称为弹性湍流（Elastic Turbulence, ET）。ET可以在小规模实验室环境中产生，与增强微流体装置中的混合效率和传热相关。在本研究中，我们研究了在以趋于零的Re和高Weissenberg数（Wi）的流入条件为特征的ET条件下，稀薄聚合物溶液的水力和热特性。我们使用Rheotool对Oldroyd-B粘弹性流体的二维曲线通道流动进行了广泛直接数值模拟。我们分析了摩擦系数和Nusselt数沿蛇形通道的变化，以揭示ET的全局和局部特征。基于Wi，我们识别出三个区域。首先，对于0 < Wi < 3，我们观察到与层流相比约10%的传热增强，同时摩擦系数降低约5%，这被称为聚合物诱导的热导率增强。其次，对于3 < Wi < 5，我们观察到传热急剧线性增加（约30%），代价是摩擦系数增强高达15%。最后，在充分发展的弹性湍流区域（Wi > 5），我们观察到高达60%的传热增强，同时伴随摩擦系数降低。随着Wi增加，传热的显著增强主要归因于由法向应力和流线曲率之间的平衡引起的弹性不稳定性的强度增加。
英文摘要：
In the presence of elastic forces, even dilute polymer suspensions can exhibit erratic flow fluctuations even when the viscous forces dominate over the inertial forces, which occur at vanishing-low Reynolds numbers (Re). This phenomenon is called Elastic Turbulence (ET). ET can be generated in small-scale laboratory settings and is relevant to enhancing mixing efficiency and heat transfer in microfluidic devices. In this study, we investigate the hydraulic and thermal properties of a dilute polymer solution under ET conditions characterized by inflow conditions of vanishing Re and high Weissenberg numbers (Wi). We carry out extensive direct numerical simulations of the 2D curvilinear channel flow of an Oldroyd-B viscoelastic fluid using Rheotool. We analyze the variations of friction factor and Nusselt numbers along the serpentine channel to reveal the global and local characteristics of ET. Based on Wi, we identify three regimes. First, for 0 < Wi < 3, we observe roughly 10% heat transfer enhancement accompanied by roughly 5% reduction of friction factor compared to laminar flow, known as polymer-induced thermal conductivity enhancement. Second, for 3 < Wi < 5, we observe a sharp linear increase of heat transfer (roughly 30%) at the cost of up to 15% enhanced friction factor. Finally, in the fully developed elastic turbulence regime (Wi > 5), we observe up to 60% heat transfer enhancement accompanied by reduced friction factor. The substantial enhancement of heat transfer with increasing Wi is mainly attributed to the increasing intensity of the elastic instability resulting from the balance between normal stresses and streamlined curvatures.
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