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Effects of buoyancy and thermophysical property variations on the flow of supercritical carbon dioxide
International Journal of Heat and Fluid Flow ( IF 2.6 ) Pub Date : 2020-12-01 , DOI: 10.1016/j.ijheatfluidflow.2020.108697
Jundi He , Junjie Yan , Wei Wang , Peixue Jiang , Shuisheng He

Abstract The flow and heat transfer behaviours of fluids at supercritical pressure have been studied using direct numerical simulations (DNS), in which one or more thermal properties are artificially frozen to discern the various physical mechanisms from each other so as to better understand the complex phenomena. Different from previous similar studies on this topic, this study focuses on the axial flow development resulted from the large variations of thermophysical properties. The contribution of the flow inertia has been quantified by analysing the momentum balance for each case studied, which has been found to be significant throughout the entire length of the pipe in cases when buoyancy is considered. The effect of the inertia on momentum in turn impacts on turbulence production, generally delaying flow laminarisation. Such an influence of flow development is non-trivial and cannot be omitted in flow analysis and heat transfer calculations. This suggests that the results of simplified analyses based on a spatially developed flow cannot be directly applied to such flows despite they can be very useful in developing fundamental understanding of the physics. Similarly, this also explains that in some cases, buoyancy parameters based on local flow quantities cannot describe heat transfer deterioration accurately. The effect of variable viscosity alone can cause turbulence reduction by flattening the velocity profile, but it will not turn the velocity profile to an M-shape, which can only be achieved by buoyancy.

中文翻译:

浮力和热物性变化对超临界二氧化碳流动的影响

摘要 使用直接数值模拟 (DNS) 研究了超临界压力下流体的流动和传热行为,其中一种或多种热特性被人为冻结以区分各种物理机制,从而更好地理解复杂现象。 . 与以往类似的研究不同,本研究侧重于热物理性质变化较大导致的轴流发展。通过分析所研究的每个案例的动量平衡,已经量化了流动惯性的贡献,在考虑浮力的情况下,已经发现在整个管道长度上,动量平衡是显着的。惯性对动量的影响反过来又会影响湍流的产生,通常会延迟流动的层流化。流动发展的这种影响是重要的,在流动分析和传热计算中不能忽略。这表明基于空间发展流动的简化分析的结果不能直接应用于这种流动,尽管它们在发展对物理学的基本理解方面非常有用。同样,这也解释了在某些情况下,基于局部流量的浮力参数无法准确描述传热恶化。单独可变粘度的影响可以通过使速度剖面变平来减少湍流,但不会将速度剖面变成 M 形,这只能通过浮力来实现。这表明基于空间发展流动的简化分析的结果不能直接应用于这种流动,尽管它们在发展对物理学的基本理解方面非常有用。同样,这也解释了在某些情况下,基于局部流量的浮力参数无法准确描述传热恶化。单独可变粘度的影响可以通过使速度剖面变平来减少湍流,但不会将速度剖面变成 M 形,这只能通过浮力来实现。这表明基于空间发展流动的简化分析的结果不能直接应用于这种流动,尽管它们在发展对物理学的基本理解方面非常有用。同样,这也解释了在某些情况下,基于局部流量的浮力参数无法准确描述传热恶化。单独可变粘度的影响可以通过使速度剖面变平来减少湍流,但不会将速度剖面变成 M 形,这只能通过浮力来实现。基于局部流量的浮力参数不能准确描述传热恶化。单独可变粘度的影响可以通过使速度剖面变平来减少湍流,但不会将速度剖面变成 M 形,这只能通过浮力来实现。基于局部流量的浮力参数不能准确描述传热恶化。单独可变粘度的影响可以通过使速度剖面变平来减少湍流,但不会将速度剖面变成 M 形,这只能通过浮力来实现。
更新日期:2020-12-01
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