Study on Key Parameters of Flow Element for Particle Samplers

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%.