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Analysis of entropy generation in double-diffusive natural convection of nanofluid

机译：纳米流体双扩散自然对流中的熵产生分析

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摘要

In the present work, entropy generation analysis on double-diffusive natural convection of nanofluid in a rectangular enclosure is conducted to deepen our insights into the performance of solar thermal systems. The effects of thermal Rayleigh number, ratio of buoyancy forces, nanoparticle volume fraction and aspect ratio of enclosure are discussed in details. It is found that entropy generation will be enhanced more intensively in turbulent regimes. The total entropy generation will reach its minimum when the ratio of buoyancy forces is unity. The total entropy generation is a monotonic decreasing function of nanoparticle volume fraction. It is interesting that the irreversibility due to thermal diffusion, viscous dissipation and concentration diffusion will change about the same rate with nanoparticle volume fraction. The differences and similarities between nanofluid and pure base fluid are also analyzed. In some scenarios, the data based on the second law of thermodynamics are better than that based on the first law of thermodynamics to describe the difference between heat and mass transfer intensity. Moreover, we find a kind of self-organized phenomenon, which we firstly observed in double-diffusive natural convection of air, also exists in its nanofluid counterpart. Especially, even in fully turbulent regimes, there appear order structures in the picture of relative entropy generation. Such phenomenon can be used as an indicator to find order in complicated flow.
机译：在目前的工作中，对矩形外壳中纳米流体的双扩散自然对流进行熵产生分析，以加深我们对太阳能热系统性能的认识。详细讨论了热瑞利数，浮力比，纳米颗粒体积分数和围护结构的长宽比的影响。已经发现，在湍流状态下，熵的产生将得到更强烈的增强。当浮力的比率为1时，总熵产生将达到最小值。总熵产生是纳米颗粒体积分数的单调递减函数。有趣的是，由于热扩散，粘性耗散和浓度扩散引起的不可逆性将随着纳米颗粒体积分数而以大约相同的速率变化。还分析了纳米流体与纯基础流体之间的差异和相似性。在某些情况下，基于热力学第二定律的数据要好于基于热力学第一定律的数据来描述传热和传质强度之间的差异。此外，我们发现一种自组织现象，我们首先在空气的双扩散自然对流中观察到，也存在于它的纳米流体对应物中。特别是，即使在完全湍流的情况下，在相对熵产生的图中也会出现有序结构。这种现象可以用作指示复杂流程中的顺序的指标。

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