Effects of polymer additives on heat transport and flow structure in Rayleigh-Bénard convection

IF 5.8 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer Pub Date : 2025-05-17 DOI:10.1016/j.ijheatmasstransfer.2025.127193

Ning Wei, Yi-Chao Xie

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引用次数: 0

Abstract

We experimentally investigate the effects of polymer additives in turbulent Rayleigh-Bénard convection (RBC) in a cubic cell with an aspect ratio

Γ = 1

. The heat transport efficiency is measured with the polymer concentration

c

varied in the range of

0 \leq c \leq 200

ppm and the

W i

number in the range of

0.15 \leq W i \leq 1.45

. In addition, the structure of the large-scale flow, the dynamics of the velocity boundary layer, and the velocity and temperature statistics in the bulk flow are investigated at various polymer concentrations

c

. It is found that polymer additives reduce the global heat transport. The degree of the reduction increases with

c

for fixed

W i

and decreases with

W i

for fixed

c

. Measurements of the flow structure show that when

c

exceeds a threshold of approximately 60 ppm, the large-scale circulation typically observed in turbulent RBC is replaced by vertically moving thermal plumes. This change in flow structure is also reflected in the statistics of the temperature and velocity in the bulk flow, i.e., the bulk flow becomes more coherent and the vertical velocity fluctuations are enhanced. It is also found that polymer additives stabilize the boundary layer by reducing both the velocity magnitude and velocity fluctuation. This stabilization leads to the thickening of the velocity boundary layer. These findings shed new light on how polymer additives affect the flow structure and heat transport in turbulent thermal convection.

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聚合物添加剂对瑞利-巴氏对流传热及流动结构的影响

实验研究了聚合物添加剂在纵横比Γ=1的立方胞体中对湍流瑞利-巴姆纳德对流（RBC）的影响。当聚合物浓度c在0≤c≤200 ppm范围内变化，Wi值在0.15≤Wi≤1.45范围内变化时，对热传导效率进行了测量。此外，研究了不同聚合物浓度下大尺度流动的结构、速度边界层的动力学以及整体流动中的速度和温度统计数据。结果表明，聚合物添加剂减少了整体热输运。对于固定的Wi，减少的程度随c的增加而增加，而对于固定的c，减少的程度随Wi的减少而减少。流动结构的测量表明，当c超过大约60 ppm的阈值时，通常在湍流RBC中观察到的大规模循环被垂直移动的热羽流所取代。这种流动结构的变化也反映在对体流温度和速度的统计上，即体流变得更加相干，垂直速度波动增强。聚合物添加剂通过降低速度大小和速度波动来稳定边界层。这种稳定化导致速度边界层增厚。这些发现揭示了聚合物添加剂如何影响湍流热对流中的流动结构和热传递。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

International Journal of Heat and Mass Transfer 工程技术-工程：机械

CiteScore

10.30

自引率

13.50%

发文量

1319

审稿时长

41 days

期刊介绍： International Journal of Heat and Mass Transfer is the vehicle for the exchange of basic ideas in heat and mass transfer between research workers and engineers throughout the world. It focuses on both analytical and experimental research, with an emphasis on contributions which increase the basic understanding of transfer processes and their application to engineering problems. Topics include: -New methods of measuring and/or correlating transport-property data -Energy engineering -Environmental applications of heat and/or mass transfer