Enhancing radial temperature uniformity and boundary layer development in viscous Newtonian and non-Newtonian flow by transverse oscillations: A CFD study
Enhancing radial temperature uniformity and boundary layer development in viscous Newtonian and non-Newtonian flow by transverse oscillations: A CFD study
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DOI：
10.1016/j.ces.2009.12.022
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发表时间：
2010-03
影响因子：
4.7
通讯作者：
M. Eesa;M. Barigou
中科院分区：
文献类型：
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作者：
M. Eesa;M. Barigou
层流管流中的径向换热仅限于慢速导热，导致管子横截面上的温度分布较宽。这在许多工业过程中是不可取的，因为它导致了流体热处理的不均匀分布。通常涉及的流体是相对粘性的，在湍流条件下处理它们是不切实际的和/或不经济的。另一方面，在卫生工艺中可能禁止使用静态直列式搅拌器来促进径向混合，因为它们很难保持清洁。本文利用一个有效的计算流体动力学(CFD)模型来证明，在定常层流上施加横向振动运动会产生足够的混沌流体运动，从而导致大量的径向混合。这导致了壁面换热的显著增强，以及近乎均匀的径向温度场，并伴随着流动内部区域的大量加热。振动还会导致温度分布在轴向迅速发展，使热进口长度大大减少，因此原则上可以使用更短的管道来实现所需的出口温度。对于不同粘度的牛顿和非牛顿假塑性流体，在很大的振动幅度和频率范围内，这种影响都被定量地证明了。对于可以实现振动运动的过程，好处可能是非常显著的。
Radial heat transfer in laminar pipe flow is limited to slow thermal conduction which results in a wide temperature distribution over the pipe cross-section. This is undesirable in many industrial processes as it leads to an uneven distribution of fluid heat treatment. Often the fluids involved are relatively viscous and processing them under turbulent conditions is impractical and/or uneconomical. On the other hand, the use of static in-line mixers to promote radial mixing may be prohibited in hygienic processes because they are difficult to keep clean. In this paper, we use a validated Computational Fluid Dynamics (CFD) model to show that the imposition of a transverse vibration motion on a steady laminar flow generates sufficient chaotic fluid motion which leads to considerable radial mixing. This results in a large enhancement in wall heat transfer as well as a near-uniform radial temperature field accompanied by a substantial heating of the inner region of the flow. Vibration also causes the temperature profile to develop very rapidly in the axial direction reducing the thermal entrance length by a large factor, so that much shorter pipes could in principle be used to achieve a desired temperature at the outlet. The effects are quantitatively demonstrated for Newtonian and non-Newtonian pseudoplastic fluids of different viscosities, for a wide range of vibration amplitudes and frequencies. For processes where vibrational motion can be implemented the benefits can be very significant.