Thermal Mass Flow Controller Induced Temperature Fluctuations in a Gas Flow Calibration Line at NMISA

W. M. Dlamini, R. M. Molefe
The National Metrology Institute of South Africa’s (NMISA) gas flow laboratory uses TMFCs to control gas flow rate during calibration of gas flow meters. The TMFC is connected upstream of the unit under test (UUT) during calibration. The laboratory performs gas flow calibrations in the range 5 mL/min – 50 L/min using nitrogen as flow medium. The gas temperature at the UUT’s location downstream of an TMFC has been found to fluctuate proportionally to the change in the flow rate at flow rates above 250 mL/min and below 22.5 L/min. This temperature fluctuation has a significant effect on measurements by volumetric gas flow meters not installed with temperature and pressure sensors. The temperature fluctuations are attributed to heat generated by the MFC electronics and transferred via thermal convection currents, and the heat absorbed by the gas flowing through the capillary sensor tube. This paper discusses gas temperature fluctuations observed at the NMISA flow laboratory as gas flow rate is changed using a TMFC. It also discusses a calibration setup used to measure temperature and pressure at the UUT’s location for volumetric gas flow meters without temperature and pressure sensors. These temperature and pressure measurements allow the metrologist to convert volumetric flow rate to mass (standardised) flow rate at a specific temperature (Ts) for instruments such as bubble flow meters. The temperature Ts is chosen such that it matches field temperature as close as possible.
Gas Flow; Thermal Mass Flow Controller
Event details
Event name:

19th International Flow Measurement Conference 2022

Chongqing, CHINA
01 November 2022 - 04 November 2022