Abstract Responding to the rapid growth of size reduction in engineering systems, it is crucial to explore the safety performance of supercritical fluid systems in miniature tubes. In this paper, numerical studies are conducted to explore the performance of baffles on heat transfer deterioration (HTD) mitigations for supercritical CO2 (sCO2) flowing in a horizontal mini tube using RNG k-e turbulence model with enhanced wall treatment (EWT). Three kinds of baffle arrangements: in-lined, staggered and centred, with the same blockage ratio (BR = 0.25) are selected to explore their performance on HTD mitigation. The thermo-hydraulic performances of the baffled tubes are examined using the dimensionless parameters based on normalized Nusselt numbers and Fanning friction factors, Nu/Nu0, f/f0 and PEC = (Nu/Nu0)/(f/f0)1/3. The results reveal that unlike the in-lined and staggered baffles, the centred baffles induce jet impingements directly onto the tube walls and generate significant amounts of transverse fluid velocity near the tube wall (which exceeds that in the core region), making it the most influential baffle arrangement on the HTD mitigations. The effects of baffles on buoyancy flow under a wide range of heat and mass fluxes are explored based on Jackson’s criterion (Gr/Re2 10 3 ). It is observed that the Gr/Re2 increases at a relatively lower rate in baffled tube than in the smooth tube under increased heat flux variation whereas it decreases at a higher rate than the smooth tube under increased mass flux variation, thus revealing the buoyancy weakening effects of baffles. Finally, the baffle’s performance on HTD mitigation when the tube is further miniaturized is explored and the results unveil that miniaturization weakens buoyancy, and there exists a certain mini size (D = 0.5 mm) at which buoyancy influence completely vanishes, and the effect of baffles on HTD mitigation becomes insignificant.

中文翻译：

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超临界 CO2 在水平微型管中流动的传热劣化及其缓解的数值研究

摘要 为应对工程系统尺寸减小的快速增长，探索微型管中超临界流体系统的安全性能至关重要。在本文中，使用 RNG ke 湍流模型和增强的壁面处理 (EWT) 进行数值研究，以探索挡板对水平微型管中流动的超临界 CO2 (sCO2) 传热劣化 (HTD) 缓解的性能。选择三种挡板布置方式：直列式、交错式和居中式，具有相同的堵塞比（BR = 0.25）来探索它们在 HTD 缓解方面的性能。使用基于归一化 Nusselt 数和 Fanning 摩擦系数的无量纲参数 Nu/Nu0、f/f0 和 PEC = (Nu/Nu0)/(f/f0)1/3 来检查折流管的热工水力性能。结果表明，与内嵌和交错的挡板不同，居中的挡板直接在管壁上引起射流冲击，并在管壁附近产生大量横向流体速度（超过核心区域的速度），使其成为最对 HTD 缓解有影响的挡板布置。基于Jackson 准则(Gr/Re2 10 3 ) 探索了在大范围的热量和质量通量下挡板对浮力流的影响。观察到，在热通量变化增加的情况下，折流管中 Gr/Re2 的增加率低于光滑管，而在质量通量变化增加的情况下，Gr/Re2 减少率高于光滑管，从而揭示了浮力减弱效应的挡板。最后，