Abstract In this work, transient numerical simulations are carried out to investigate the effect of alumina nanoparticles with pure water as a base fluid on mixed convection with magnetohydrodynamic flow in a vertical channel with two facing identical open cubic cavities with discrete heating. The nanofluids are modeled using a single phase approach and the fluid properties are considered constant with temperature. The left and right vertical walls of the cavities are isothermal, all other bounding walls of the cavity and the channel are adiabatic, and a uniform magnetic field is applied in the horizontal direction. The governing Navier–Stokes equations in vorticity and stream function form coupled with the energy equation are solved using the control volume method on a nonuniform orthogonal Cartesian grid. A parametric study has been carried out for three different Hartmann numbers of ( H a = 0 ; 5 ; 10 ) Richardson numbers of ( R i = − 1 ; 5 ) , nanoparticle volume fractions of ( φ = 0 . 0 ; 0 . 1 ; 0 . 2 ) and Reynolds number ranging from 300 to 700. The effects of the nanoparticle volume fraction and magnetic field on hydrodynamic and thermal characteristics and entropy generation for assisting/opposing buoyancy have been assessed. In general, it has been found that in the range of parameters considered in this study, the entropy generation is dominated by irreversibilities due to heat transfer for all values of φ . The results show that the vortex dynamics, heat transfer characteristics and the magnitude of irreversibilities in the entropy generation are strongly affected by the strength of the magnetic field applied and the nanoparticle volume fraction. Moreover, these results suggest that the modulation effect of the applied magnetic field can play an important role in practical applications for entropy generation minimization.

中文翻译：

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Al2O3-水纳米流体在离散加热的两个面对腔通道中磁流体动力混合对流和熵产生的数值研究

摘要 在这项工作中，进行了瞬态数值模拟，以研究以纯水为基液的氧化铝纳米颗粒对垂直通道中磁流体动力流混合对流的影响，该通道具有两个面对的具有离散加热的相同开放立方腔。纳米流体使用单相方法建模，流体特性被认为随温度保持不变。腔体的左右垂直壁是等温的，腔体和通道的所有其他边界壁都是绝热的，并且在水平方向上施加均匀的磁场。使用控制体积法在非均匀正交笛卡尔网格上求解与能量方程耦合的涡度和流函数形式的控制 Navier-Stokes 方程。对三种不同的哈特曼数（H a = 0 ; 5 ; 10 ）理查森数（R i = − 1 ; 5 ），纳米颗粒体积分数（ φ = 0 . 0 ; 0 . 1）进行了参数研究。 ; 0 . 2 ) 和雷诺数范围从 300 到 700。已经评估了纳米颗粒体积分数和磁场对流体动力学和热特性以及用于辅助/对抗浮力的熵产生的影响。总的来说，已经发现在本研究中考虑的参数范围内，熵的产生主要是由于所有 φ 值的热传递引起的不可逆性。结果表明，涡流动力学，热传递特性和熵产生中的不可逆程度受所施加磁场强度和纳米颗粒体积分数的强烈影响。此外，这些结果表明外加磁场的调制效应可以在熵产生最小化的实际应用中发挥重要作用。