An experimental study was conducted to evaluate the pressure loss per unit length of nonmetallic flexible duct under fully stretched conditions when a controlled bend was present and to determine a pressure corrective K factor to compare to a straight section of the same length. All tests were conducted in accordance with ANSI/ASHRAE Standard 120-2008. Ducts of 203-, 305-, and 356-mm (8-, 12-, and 14-in.) nominal diameters were tested. The bend was created by wrapping the duct around a mandrel to generate a 45° and 90° bend. In every instance, the duct was subjected to only one bend with a dimensionless bend radius of either R/D = 1 or R/D = 1.5. The pressure loss per unit length versus flow rate was described by a power law relationship. Positive K factors were obtained when a bend was present, and it was found that the K factor typically increased as volume flow rate increased. Generally the K factor for a 90° bend approximately equaled 2.0, whereas the K factor for a 45° bend tended to have a value roughly equal to 1.25. For a given duct diameter with either a 45° bend or a 90° bend, the K factor for R/D = 1 exceeded that for R/D = 1.5. Suggestions for additional testing of flexible duct configurations more representative of typical field installations are provided.
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机译:进行了一项实验研究,以评估在存在受控弯曲的情况下在完全拉伸条件下非金属挠性管道每单位长度的压力损失,并确定与相同长度的直管段进行比较的压力校正K因子。所有测试均根据ANSI / ASHRAE标准120-2008进行。测试了203-,305-和356-mm(8-,12-和14-in。)公称直径的导管。弯曲是通过将导管缠绕在心轴上以产生45°和90°弯曲而产生的。在每种情况下,导管仅经受一次弯曲,其无因次弯曲半径为R / D = 1或R / D = 1.5。每单位长度的压力损失与流速之间的关系由幂律关系描述。当存在弯曲时,获得正的K因子,并且发现K因子通常随体积流量的增加而增加。通常,90°弯曲的K系数大约等于2.0,而45°弯曲的K系数往往具有大约1.25的值。对于具有45°弯曲或90°弯曲的给定管道直径,R / D = 1的K因子超过R / D = 1.5的K因子。提供了对柔性管道配置进行更多测试的建议,这些建议可以更好地代表典型的现场安装。
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