Validation of the gravimetric Thermal Energy standard flow facility after extensive modernisation

The performance of the GraTESt (Gravimetric Thermal Energy Standard) flow facility of the Physikalisch-Technische Bundesanstalt (National Metrology Institute of Germany) was revalidated after extensive modernisation. The expanded measurement uncertainty for the test volume was determined for the operational range of flow rate and temperature and did not exceed 0.034 % (k = 2), thereby supporting the projected measurement uncertainty of 0.040 % (k = 2). A bilateral comparison between the present facility and the High-Reff facility at the National Metrology Institute of Japan was performed with a turbine flow meter as the transfer standard. The comparison yielded good agreement with the standardized degree of equivalence E n not exceeding 0.52.