Abstract

Twisted tape inserts are commonly used for heat transfer enhancement in fusion applications. Although these devices have been extensively studied, existing correlations relating friction factor to Reynolds number and system geometry are applicable only for tight-fitting inserts and cannot account for system roughness and fouling. In this work, we examine pressure losses in twisted tapes of various twist ratios using both a typical twisted tape correlation and a newer formulation that incorporates conventional channel flow correlations. We study flows down to a Reynolds number of 4000 and find that the channel flow treatment predicts experimental outcomes well for turbulent conditions, like those expected in the ITER divertor. For calculations at low Reynolds numbers (expected during start-up and show-down of the divertor), we propose that channel flow correlations be merged with twisted tape correlations. This new, merged correlation is seen to be applicable across all Reynolds numbers observed, although it predicts small divergences among tape pitches at low Reynolds numbers that are not clearly reflected in our experimental data. Experimental and legacy data show that conventional channel flow friction factor correlations can be used under this formulation for pressure drop predictions at Reynolds number above 15 000. We suggest the use of this twisting channel treatment for loose-fitting inserts and systems in which fouling and roughness may be of concern, allowing existing straight channel models to be used for twisted tape pressure drop calculations.

摘要

扭曲的带状插入件通常用于增强融合应用中的传热效果。尽管已经对这些装置进行了广泛的研究，但现有的将摩擦系数与雷诺数和系统几何形状相关的相关性仅适用于紧密配合的刀片，无法解决系统的粗糙度和结垢问题。在这项工作中，我们使用典型的扭曲带相关性和结合了常规通道流量相关性的更新公式，研究了各种扭曲比的扭曲带中的压力损失。我们研究了雷诺数为4000的流量，发现通道流动处理可以很好地预测湍流条件下的实验结果，如ITER偏滤器中预期的那样。对于低雷诺数的计算（预期在分流器启动和显示期间），我们建议将通道流相关性与扭曲带相关性合并。尽管这种新的合并相关性适用于观察到的所有雷诺数，但可以预测出在低雷诺数时磁带间距之间的微小差异，这在我们的实验数据中并未清楚体现。实验数据和传统数据表明，在此公式下，常规通道流摩擦因子相关性可用于雷诺数大于15000时的压降预测。我们建议将此扭曲通道处理用于松配合的嵌件和其中结垢和粗糙度大的系统可能会令人担忧，从而允许将现有的直通道模型用于扭曲带压降计算。合并的相关性被认为适用于所观察到的所有雷诺数，尽管它预测了在低雷诺数下磁带间距之间的微小差异，这在我们的实验数据中并未清楚体现。实验数据和传统数据表明，在此公式下，常规通道流摩擦因子相关性可用于雷诺数大于15000时的压降预测。我们建议将此扭曲通道处理用于松配合的嵌件和其中结垢和粗糙度大的系统可能会令人担忧，从而允许将现有的直通道模型用于扭曲带压降计算。合并的相关性被认为适用于所观察到的所有雷诺数，尽管它预测了在低雷诺数下磁带间距之间的微小差异，这在我们的实验数据中并未清楚体现。实验数据和传统数据表明，在此公式下，常规通道流摩擦因子相关性可用于雷诺数大于15000时的压降预测。我们建议将此扭曲通道处理用于松配合的嵌件和其中结垢和粗糙度大的系统可能会令人担忧，从而允许将现有的直通道模型用于扭曲带压降计算。