Critical flow nozzles are widely used as secondary standards in gas flow measurement. In the context of critical flow nozzles, carbon dioxide (CO▫$_2$▫) is of particular interest for investigation due to its properties and its increasingly widespread use. Since CO▫$_2$▫ typically contains impurities in practical systems, this study focuses on the measurement of CO▫$_2$▫ flow with impurities, represented by nitrogen (N▫$_2$▫). The primary result of each measurement is the discharge coefficient as a function of the Reynolds number. The discharge coefficient is a nozzle-specific parameter that depends on the working fluid and operating conditions and is defined as the ratio of the actual mass flow rate to the theoretical mass flow rate. The nozzles were first calibrated using air, pure CO▫$_2$▫, and N▫$_2$▫, and the experimental results were compared with theoretical model predictions and previous calibration data. A dedicated measurement system for generating gas mixtures was subsequently established. Gas mixtures were prepared using calibrated mass flow controllers, while a piston prover was employed as the reference flow measurement device. A linear relationship between the discharge coefficient and the N▫$_2$▫ fraction in the gas mixture was demonstrated. Measurement uncertainty was evaluated for all measurements.
|
