两个平行板间纳米流体瑞利- b纳德流动的演化:介观模拟研究

Gui Lu, Y. Duan, Xiao-dong Wang
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引用次数: 2

摘要

采用介观热晶格-玻尔兹曼方法(LBM)模拟了两个平行板之间的纳米流体Rayleigh - Benard流动。采用不同颗粒体积分数(1 ~ 4%)考察了热导率和动态粘度对瑞利-贝纳德流动演化的耦合效应,采用不同粒径(11nm、20nm和30nm)和纳米颗粒类型(Al2O3、Cu和CuO2)考察了热导率和动态粘度的单独影响。还考虑了两种不同的加热模式。结果表明,纳米流体中的瑞利-贝纳德细胞与纯流体中的瑞利-贝纳德细胞有明显不同。纳米流体中稳定的对流细胞来自于初始涡对的膨胀和脱落,而在纯水中,当瑞利数达到临界值时,流动突然开始。因此,纳米流体的平均努塞尔数逐渐增加,而纯液体的平均努塞尔数急剧增加。与纯液体相比,纳米流体的底部加热产生了均匀、充分发展的流动单元,涡对较少但较大,顶部加热时极微小的涡被限制在顶部加热板附近。随着纳米颗粒体积分数和粒径的增加,由于动态粘度的增加,涡流对的数量减少。平均努塞尔数随瑞利数的增加而增加,随纳米颗粒直径的增加而减小。纳米颗粒类型对瑞利-贝纳德流型影响不大。相对于纳米流体的热导率,瑞利-贝纳德流动对动态粘度更为敏感。(DOI: 10.1115/1.4027987)
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Evolution of Nanofluid Rayleigh–Bénard Flows Between Two Parallel Plates: A Mesoscopic Modeling Study
The developing and developed nanofluid Rayleigh‐Benard flows between two parallel plates was simulated using the mesoscopic thermal lattice-Boltzmann method (LBM). The coupled effects of the thermal conductivity and the dynamic viscosity on the evolution of Rayleigh‐Benard flows were examined using different particle volume fractions (1‐4%), while the individual effects of the thermal conductivity and the dynamic viscosity were tested using various particle sizes (11nm, 20nm, and 30nm) and nanoparticle types (Al2O3, Cu, and CuO2). Two different heating modes were also considered. The results show that Rayleigh‐Benard cell in nanofluids is significantly different from that in pure fluids. The stable convection cells in nanofluids come from the expansion and shedding of an initial vortex pair, while the flow begins suddenly in pure water when the Rayleigh number reaches a critical value. Therefore, the average Nusselt number increases gradually for nanofluids but sharply for pure liquids. Uniform fully developed flow cells with fewer but larger vortex pairs are generated with the bottom heating with nanofluids than with pure liquid, with extremely tiny vortexes confined near the top heating plate for top heating. The number of vortex pairs decreases with increasing nanoparticle volume fraction and particle diameter due to the increasing of dynamic viscosity. The average Nusselt number increases with the increasing Rayleigh number, while decreases with the increasing nanoparticle diameters. The nanoparticle types have little effect on the Rayleigh‐Benard flow patterns. The Rayleigh‐Benard flows are more sensitive with the dynamic viscosity than the thermal conductivity of nanofluids. [DOI: 10.1115/1.4027987]
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