Performance Evaluation of Critical Flow Venturi Nozzle with Primary Standard Calibration Facilities at FCRI and Validation with ISO Standards

摘要

A 2" NB Critical Flow Venturi Nozzle (CFVN) of Nominal Flow capacity 25m~(3)/h was designed at Fluid Control Research Institute (FCRI), India as a transfer standard for undertaking calibration of smaller capacity flow meters. The Nozzle fabricated was of Toroidal throat design and was assembled as per the general guidelines of ISO 9300:2005 "Measurement of gas flow by means of Critical flow Venturi nozzles". The Air Flow Measurement facilities at FCRI is equipped with Primary Standards Pressure-Volume-Temperature-time (PVTt) facility of 2m3 Nominal volume and 90 m~(3)/h maximum flow capacity and a Bell Prover of 500 ltr volume and with a maximum flow capacity of 40m~(3)/h. The performance of the Critical Flow Venturi Nozzle assembly was tested and analyzed with both PVTt facility and Bell Prover. PVTt facility can be used as a collection tank for estimation of mass flow rate during operation of CFVN during suction mode. To establish dynamic traceability in measurements and compare the test results with other proven primary standards, the same CFVN assembly was calibrated both under pressure mode and suction mode using the Primary standard Bell Prover system available at the Primary Standard Air Flow Laboratory at FCRI. During filling mode operation of Bell Prover, the Throat Reynolds number of nozzle was about 1.24E+05 and in Discharge mode of flow test the Throat Reynolds number of nozzle was about 8.61E+04. Cd of the nozzle was established at different Reynolds numbers with both PVTt facility and Bell prover. The results obtained with the above methods were validated using ISO equation given in ISO 9300: 2005.