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首页> 外文期刊>International Journal of Heat and Mass Transfer >Buoyancy driven flow and heat transfer of nanofluids past a square cylinder in vertically upward flow
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Buoyancy driven flow and heat transfer of nanofluids past a square cylinder in vertically upward flow

机译：浮力驱动的流动和纳米流体在垂直向上流动中经过方形圆柱体的传热

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摘要

The present work simulates the buoyancy driven mixed convective flow and heat transfer characteristics of water-based nanofluid past a square cylinder in vertically upward flow using a SUPG (Streamline Upwind Petrov-Galerkin) based finite element method. Nano sized copper (Cu) and alumina (Al_2O_3) particles suspended in water are used with Prandtl number (Pr) = 6.9. The range of nanopartide volume fractions (φ) considered is 0 ≤ φ ≤ 20%. Computations are carried out at a representative Reynolds number (Re) of 100. Effect of aiding and opposing buoyancy is brought about by considering the Richardson number (Ri) range -0.5 ≤ Ri ≤ 0.5. Al_2O_3water and Cu-water nanofluids show suppression of vortex shedding at Ri ≥ 0.15. Vortex shedding process is initiated and a completely new phenomenon is discovered when the nanofluid solid volume fraction,φ, is increased. For Al_2O_3-water nanofluids, at Ri = 0.15, completely periodic vortex shedding is found for φ ≥ 10%. For Cu-water nanofluid, shedding is observed for both Ri=0.15 and Ri = 0.5. At Ri=0.15 shedding is found at φ ≥ 5%, w_Hereas at Ri=0.5 it is at φ ≥ 15%. A new expression for convective instability of nanofluids is derived to calculate critical nanofluid solid volume fraction. The local Nusselt number increases with increasing φ. At a fixed φ, the time averaged local Nusselt number is higher for Cu-water nanofluids, as compared to Al_2O_3-water nanofluids. The average Nusselt number (Nu_(avg)) increases with the concentration of φ. Cu-water based nanofluids show higher magnitudes of Nu_(avg) compared to Al_2O_3-water nanofluids.
机译：本工作使用基于SUPG（Streamline Upwind Petrov-Galerkin）的有限元方法模拟了水动力纳米流体在垂直向上流动时通过方形圆柱体的浮力驱动的混合对流流动和传热特性。使用悬浮在水中的纳米级铜（Cu）和氧化铝（Al_2O_3）颗粒，其Prandtl数（Pr）= 6.9。所考虑的纳米粒子体积分数（φ）的范围为0≤φ≤20％。以代表性的雷诺数（Re）为100进行计算。考虑到理查森数（Ri）的范围-0.5≤Ri≤0.5，可产生辅助和相反的浮力效果。 Al_2O_3水和铜水纳米流体在Ri≥0.15时抑制了涡旋脱落。当增加纳米流体固体体积分数φ时，便开始了涡旋脱落过程，并发现了一种全新的现象。对于Al_2O_3-水纳米流体，在Ri = 0.15时，对于φ≥10％，发现了完全周期性的涡旋脱落。对于铜水纳米流体，在Ri = 0.15和Ri = 0.5处均观察到脱落。在Ri = 0.15时，在φ≥5％处发现脱落，在Ri = 0.5时的w_Hereas在φ≥15％处发现。推导了纳米流体对流不稳定性的新表达式，以计算临界纳米流体固体体积分数。局部Nusselt数随φ的增加而增加。在固定的φ下，与Al_2O_3-水纳米流体相比，铜水纳米流体的时均局部Nusselt数更高。平均努塞尔数（Nu_（avg））随着φ的浓度而增加。与Al_2O_3-水纳米流体相比，Cu-水基纳米流体显示出更高的Nu_（avg）量级。

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