Calculation and analysis of critical flow Venturi nozzle discharge coefficient
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维普
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临界流文丘里喷嘴是一种高性能的流量计量器具,常作为气体流量计量标准应用于标准装置中,而流出系数是其最重要的计量性能参数之一,通常可溯源至pVTt法气体流量标准装置,采用实流标定的方法进行量值确认,也可以采用经验公式进行计算.目前经验公式有两种,一种为JJG 620-2008《临界流文丘里喷嘴》中给出的经验公式,一种为ISO 9300:2022 Measurement of gas flow by means of critical flow nozzles中给出的经验公式,两种公式具有相同的雷诺数适用范围,但其考虑的流出系数影响因素不同,计算结果有一定差异.该文对两种经验公式计算流出系数的结果与pVTt基准装置实流标定的流出系数结果进行了对比,结果表明,两种半经验公式在边界层湍流区域的计算结果相一致,在层流区域和转捩区域存在较大差异.另外,测试喷嘴均在层流状态下进行实流标定,且其标定结果与两种半经验公式的计算结果存在差异,建议在实际使用时对喷嘴的流出系数进行修正.
The critical flow Venturi nozzle is a high-performance flow measuring instrument,often used as a gas flow measurement standard in standard equipment,and the outflow coefficient is one of its most important measurement performance parameters,which can be traced back to the pVTt gas flow stand-ard equipment.The measurement value is confirmed using real flow calibration method,and empirical for-mulas can also be used for calculation.There are currently two empirical formulas,one is the empirical for-mula given in JJG 620-2008"Critical Flow Venturi Nozzles",and the other is the empirical formula given in ISO9300:2022 Measurement of gas flow by means of critical flow nozzles.The two formulas have the same Reynolds number applicable range,but they consider different factors affecting the outflow coeffi-cient,resulting in certain differences in the calculation results.This article compares the results of two em-pirical formulas for calculating the outflow coefficient with the results of the actual flow calibration of the pVTt reference device.The results show that the calculation results of the two semi empirical formulas are consistent in the boundary layer turbulent region,but there are significant differences in the laminar and transition regions.In addition,the test nozzles were all calibrated under laminar flow conditions,and the calibration results were different from the calculation results of two semi empirical formulas.It is recom-mended to correct the flow coefficient of the nozzles during actual use.
critical flow Venturi nozzledischarge coefficientreynolds numbercritical back pressure
维普
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