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首页> 外文期刊>International Journal of Heat and Mass Transfer >Measurements and correlations of frictional single-phase and two-phase pressure drops of R-410A flow in small U-type return bends
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Measurements and correlations of frictional single-phase and two-phase pressure drops of R-410A flow in small U-type return bends

机译：小U型弯头中R-410A流动的单相和两相摩擦压降的测量及相关性

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摘要

This study presents single-phase and two-phase frictional data for R-410A in four U-type return bends with tube diameter D = 3.3 and 5.07 mm and curvature ratio (2R/D) ranged from 3.91 to 8.15, and their frictional performances are investigated. The friction factor f_C and two-phase pressure gradient in the return bend considerably increase with the decrease of curvature ratio. For D = 5.07 mm and G ≥ 200 kg m~2 s~(-1), the ratio of (dp/dz)_C/(dp/dz)_S is relatively independent of the vapor quality x. However, a considerable rise of this ratio is encountered at x < 0.5 and G = 100 kg m~(-2) s~(-1). The significant increase of this ratio may be attributed to the change of flow pattern from stratified flow to annular flow. In contrast, for D = 3.3 mm and G ≥ 300 kg m~(-2) s~(-1), the higher pressure gradient ratio at lower x was not observed. The flow pattern at low vapor quality is slug flow and no dramatic change of flow pattern across the return bend is seen. For the single-phase results, existing correlations give fair agreements with the present f_C data. For two-phase results, the Geary correlation shows a better agreement with the data. A modified two-phase friction factor based on the Geary correlation is then proposed. The proposed correlation gives a good agreement to the present R-410A data and Geary's R-22 data with a mean deviation of 19.1%.
机译：这项研究提供了R-410A在四个U型弯管中的单相和两相摩擦数据，其管径D = 3.3和5.07 mm，曲率比（2R / D）在3.91至8.15之间，其摩擦性能被调查。随着曲率比的减小，回弯处的摩擦系数f_C和两相压力梯度会显着增加。对于D = 5.07 mm和G≥200 kg m〜2 s〜（-1），（dp / dz）_C /（dp / dz）_S的比率相对独立于蒸气质量x。但是，在x <0.5且G = 100 kg m〜（-2）s〜（-1）时，该比例会显着提高。该比率的显着增加可归因于从分层流到环形流的流型变化。相反，对于D = 3.3 mm和G≥300 kg m〜（-2）s〜（-1），在较低x处未观察到较高的压力梯度比。低蒸汽质量下的流型为团状流，在回弯处流型没有明显变化。对于单相结果，现有的相关性与当前的f_C数据具有合理的一致性。对于两阶段结果，Geary相关性显示出与数据更好的一致性。然后提出了一种基于Geary相关性的改进的两相摩擦系数。拟议的相关性与目前的R-410A数据和Geary的R-22数据非常吻合，平均偏差为19.1％。

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