单弯头条件下A+K流量计前直管段长度研究

Research on the straight pipe length of A+K flowmeter when single elbow is installed in the upstream

A+K平衡流量计是由美国国家航空航天局马歇尔航空飞行中心设计发明的一种新型的差压式流量仪表,与其他的差压式流量计相比,它具有精确度高、量程比宽、直管段短等多项优点。本文针对其所需的直管段长度短的优点,研究了等效直径比分别为0.25/0.45/0.7,口径为50 mm的3种结构的A+K平衡流量计,在上游安装单个90°弯头时所需的最短直管段长度。通过对实流实验和仿真实验获取的数据结果进行定性和定量的分析来预测上游安装单个90°弯头时不同直管段长度对A+K平衡流量计流出系数的影响,并将平均流出系数相对误差和附加不确定度作为单弯头安装条件对流量计性能影响的评价指标,最后给出上游安装单个90°弯头的最短直管段长度。

A ＋ K balance flowmeter is a new type of differential pressure flowmeter, which was invented by NASA Marshall Space Flight Center. Compared with other differential pressure flowmeters, it has many advantages such as high precision, wide range ratio, requiring short straight pipe and so on. Aiming at the advantage of requiring short straight pipe, this paper studies the minimum required length of straight pipe when single 90° elbow is installed in the upstream for three kinds of A ＋ K balance flowmeters with equivalent diameter ratios of 0. 25/0. 45/0. 7 , respectively and caliber of 50 mm. Based on the qualitative and quantitative analysis of the experimental data obtained from real flow experiment and simulation experiment, the effects of different straight pipe lengths on the discharge coefficient of A ＋ K balance flowmeter are analyzed when single 90~ elbow is installed in the upstream. The relative error and additional uncertainty of the average discharge coefficient are taken as the performance evaluation index in the single elbow installation condition. Finally the minimum required straight pipe length when single 90° elbow is installed in the upstream is given.