Research Of The Critical Venturi Nozzles Gas Flow Facility For Small Flow And The Measurement Characteristics

As transfer standards extensively used around the world, critical venturi nozzles have advantages such as simple structure, having no mobile parts, high precision, good repeatability etc. These advantages promote the critical venturi nozzles playing an important rote in the flow measurement field. In order to apply critical venturi nozzles in verification work, a small critical venturi nozzles gas flow facility based on the research of small venture nozzles structure have been set up. The measurement characteristics of the device have been studied.A computational fluid dynamics method is employed to simulate the internal fluid field of the two kinds of nozzles with different structures through Fluent. According to the analysis of the influence on the flow characteristics caused by inlet section, throat section and diffuser section, the toroial-throat nozzles which have better discharge coeffient and critical back pressure ratio are selected as the standard meter.The overall design of a small flow sonic nozzle gas flow facility is presented in this paper. The design of hardware and mechanical units, the control system with PLC and the monitoring the data processing system based on LabVIEW software platform are completed. The functions of human-computer interaction and automatic verification are realized.A series of gas leakage and verification experiments have been carried out and uncertainty assessment of device was completed. The leakage testing show that the tightness of stagnation container was good in the static process. However, in the dynamic process, as the range of measurement is small the uncertainty which is caused by small leakage can not be neglected. Considering the uncertainty of small leakage, the expanded uncertainty of the device is 0.264%(k=2). It is satisfied the demand of the verification with the measurement range of (0.008-1.007) m3/h.