用于颗粒物采样器的流量元件关键参数的研究

Study on Key Parameters of Flow Element for Particle Samplers

针对颗粒物采样器常用流量孔口流量元件的不足,研制流量测量范围在1~120 L/min的孔板流量元件。此流量范围内对应的流量元件入口雷诺数不超过2000,基本属于层流状态,已经超出了现有各类标准规定的差压式流量元件的应用范围。为保证新设计孔板的流量性能,需给定孔板厚度E、节流孔厚度e和取压位置三个关键参数的机械加工的最大允许偏差。采用计算流体力学仿真的方式确定上述几何尺寸的参数机械加工的最大允许偏差。对于1~10 L/min的孔板,E的推荐值为1.6 mm,最大允许几何偏差为±6.25%;e的推荐值为1.16 mm,最大允许几何偏差为±2.5%。对于10~100 L/min的孔板,E的推荐值为3.2 mm,最大允许几何偏差为±6.25%;e的推荐值为2.00 mm,最大允许几何偏差为±5%。上下游采用D-D/2取压方式,上游取压位置准确度为±0.1D,下游取压位置准确度为±0.05D。基于此关键尺寸,设计加工后的层流孔板的流出系数线性度和加工一致性均优于1.5%。

This study focuses on addressing the shortcomings of commonly utilized flow orifice elements in particle samplers by developing an orifice flow element capable of measuring flow rates ranging from 1 to 120 L/min.Within this flow range,the Reynolds number at the inlet of the flow element does not exceed 2000,ensuring primarily laminar flow conditions.This exceeds the operational range of differential pressure flow elements as per existing standards.To ensure optimal flow performance of the new orifice plates,it is imperative to define the maximum allowable mechanical machining deviations for key parameters such as orifice plate thickness(E),throttling orifice thickness(e),and pressure tap locations.Computational fluid dynamics simulations were employed to determine these maximum allowable deviations in the geometric dimensions.For orifice plates operating in the 1 to 10 L/min range,the suggested E value is 1.6 mm,with a maximum allowable deviation of±6.25%,and for e,a value of 1.16 mm is recommended with a deviation of±2.5%.For the 10 to 100 L/min range,an E value of 3.2 mm is recommended with a deviation of±6.25%,and an e value of 2.00 mm with a deviation of±5%.The D-D/2 method was used for pressure tapping,with upstream accuracy being±0.1D and downstream accuracy±0.05D.Based on these key dimensions,the designed orifice plates exhibited an outflow coefficient linearity and machining consistency better than 1.5%.