GB/T 21188-2007 in English

《GB/T 21188-2007用临界流文丘里喷嘴测量气体流量》由TC124（全国工业过程测量控制和自动化标准化技术委员会）归口，TC124SC1（全国工业过程测量控制和自动化标准化技术委员会温度、流量、机械量、物位、显示仪表、执行器和结构装置分会）执行，主管部门为中国机械工业联合会。
本标准规定了测量气体质量流量的临界流文丘里喷嘴的几何尺寸和使用方法。

Scope

This standard specifies the geometric dimensions and usage method (installation and working conditions in the system) of the critical flow venturi nozzle (CFVN) for measuring gas mass flow rate, and gives the data required for calculating the flow rate and its uncertainty. It is suitable for Venturi nozzles where the gas flow is accelerated to a critical velocity (equal to the local speed of sound) at the throat, and there is only a steady flow of single-phase gas at the throat. At the critical velocity, the gas mass flow rate through the Venturi nozzle is the maximum flow rate possible under practical upstream conditions. Critical flow Venturi nozzles should only be used within the specified limits for the nozzle throat to inlet diameter ratio and throat Reynolds number. The critical flow Venturi nozzles involved in this standard have done a large number of direct calibration tests, which can ensure that the given critical flow Venturi nozzle discharge coefficient is within a predictable uncertainty limit. The data given in this standard are suitable. In the following cases: the upstream pipeline of the critical flow Venturi nozzle is a circular cross-section pipeline; or the upstream of the critical flow Venturi nozzle, or the upstream of a set of critical flow Venturi nozzles installed in groups can be regarded as a large space. This group configuration provides the possibility to install critical flow venturi nozzles in parallel, so that a larger flow rate can be obtained. For high accuracy measurement, this standard discusses the precise machining of critical flow venturi nozzles for low Reynolds numbers.