上游单弯头和闸阀对涡街流量计测量性能影响

Impact of Upstream Single Bend and Gate Valve on the Measurement Performance of Vortex Flowmeters

为了考察现场实际安装环境和使用条件对涡街流量计测量精度的影响,对DN100涡街流量计进行了基准实验、上游单个90°弯头和全开闸阀共23组实流实验.实验介质为水,雷诺数范围3.5×104～5.3×105.以平均仪表系数的相对误差、仪表系数的线性度和重复性作为评价指标,最终给出了涡街流量计在2种安装条件下的推荐前后直管段长度:雷诺数在1.0×105～5.3×105单弯头时,前直管段长度至少5,D,后直管段长度至少3,D;全开闸阀时,前直管段长度至少5,D,后直管段长度至少5,D,此时弯头和闸阀对涡街流量计的测量影响才能忽略.雷诺数在3.5×104～5.3×105时,小流量点处仪表系数的严重下降导致涡街流量计在2种安装条件下均无法达到测量精度.

In order to investigate the effect of installation requirements and application conditions on measurement accuracy, 23 groups of experiments on a vortex flowmeter with 100 mm diameter were carried out, including reference experiments, experiments on single bend and gate valve effects with different upstream and downstream straight pipe lengths. The experiment medium was water and Reynolds number range was 3.5 ×10^4--5.3 ×10^5. Three evaluating indicators were adopted to evaluate the installation effects on vortex flowmeter, such as relative error of average meter factor, linearity and repeatability. Through analysis, the shortest upstream and downstream straight pipe lengths are recommended when the installation effects can be neglected. When Re = 1.0 ×10^5--5.3×10^5, to the single bend, the length of the upstream straight pipe is at least 5 D and that of the downstream pipe is at least 3 D. While to the gate valve, both the upstream straight pipe and the downstream pipe are at least 5 D in length. When Re = 3.5 ×10^4--5.3×10^5, to both single bend and gate valve, the measurement accuracy is hardly achieved because of great decrease of meter factor at low flowrate.