用临界流量喷嘴测量气体流量

[中文适用范围]： 本文件规定了临界流量喷嘴 (CFN) 的几何形状和使用方法（在系统中安装和操作条件），用于确定流经系统的气体的质量流量，基本上无需校准 CFN。 它还提供了计算流量及其相关不确定性所需的信息。 本文件适用于气流在最小流动截面处加速至临界速度的喷嘴，并且仅适用于单相气体稳定流动的情况。 当喷嘴达到临界速度时，流过喷嘴的气体质量流量是现有入口条件下可能的最大质量流量，而CFN只能在指定限制内使用，例如CFN喉部与入口直径比和雷诺数。 本文件涉及环形和圆柱形喉部 CFN，已对其进行了足够数量的直接校准实验，以使所得系数能够在某些可预测的不确定性限制下使用。 [外文原描述]： This document specifies the geometry and method of use (installation in a system and operating conditions) of critical flow nozzles (CFNs) used to determine the mass flow rate of a gas flowing through a system basically without the need to calibrate the CFN. It also gives the information necessary for calculating the flow rate and its associated uncertainty. This document is applicable to nozzles in which the gas flow accelerates to the critical velocity at the minimum flowing section, and only where there is steady flow of single-phase gas. When the critical velocity is attained in the nozzle, the mass flow rate of the gas flowing through the nozzle is the maximum possible for the existing inlet condition, while the CFN can only be used within specified limits, e.g. the CFN throat to inlet diameter ratio and Reynolds number. This document deals with the toroidal- and cylindrical-throat CFNs for which direct calibration experiments have been made in sufficient number to enable the resulting coefficients to be used with certain predictable limits of uncertainty.