In recent years, the Coriolis mass flow meters (CMF), devices based on the Coriolis effect over a vibrating pipe, have developed better metrological performance and they are now a reasonable alternative for the custody transfer measurements. Nowadays, many custody transfer operations require measurement of the net volume (volume measured at a certain reference temperature) and, therefore, it is not feasible to use the CMF as a mass flow meter. However, the actual CMF can be used as net volume meters because they have special equipment to measure density and temperature, and a flow computer. In this work, firstly a mathematical simplification of the physical model is proposed for the CMF. We part from the dimensional analysis of the flow-phase relationship produced by the Coriolis force, the main physical principle behind these devices. A simplified formula is obtained and it permits identifying the magnitudes of influence of the CMF as a mass meter. Secondly, its metrological properties are characterized. For such purpose, a 4" straight tube commercial meter has been calibrated in volume, in the 50 to 165 m3/h range against a standard container and a bidirectional prover, employing gas oil and kerosene (JET-A1). These calibrations have turned out to be compatible with the ones performed by the manufacturer in mass and using water. Then it is verified that the CMF fulfills the requisites of the legal metrology: maximum error allowed, linearity and repeatability. Skewness is observed in the relative error (expressed in %) of the CMF and it has been researched to be due to systematic effects related to constructive parameters of the meter. Lineal correlation is verified between relative error and temperature, and between relative error and flow rate, with negative slopes of -0.03% °C-1 and -0.001% h/m3 respectively.
Keywords: Coriolis; Custody transfer; Flow meter; Intercomparison.
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