## 3 Results and Discussion
### Test Results for Pressure-Matching Approach  
The measurement characteristics of the Coriolis mass flowmeter for the pressure-matching approach were assessed using the high-pressure water flow test facility to investigate the pressure dependence of the flowmeters at hydrogen refueling stations, as shown in Figure 5. The measurement test of the pressure-matching approach was conducted with the same Coriolis mass flowmeter used in the test with the density-matching approach, shown in Figure 4. The Coriolis mass flowmeter was installed in a position where the inlet pressure of the supplied water could be controlled by a high-pressure liquid pump and two pressure regulators. The pressure range of the supplied water to the installed Coriolis mass flowmeter, adjustable in the high-pressure water flow test facility, is 2 bar to 700 bar, which is equivalent to the operating pressure conditions at a hydrogen refueling station. The flowrate conditions of the measurement test at the installed Coriolis mass flowmeter were 1 kg/min to 5 kg/min, as controlled by a control valve downstream of the high-pressure water flow facility. Figure 8 presents the test results of the Coriolis mass flowmeter when the inlet pressure of the supplied water is set to 2 bar. Five different mass flowrates ranging from 1.0 kg/min to 5.0 kg/min were used, as this is the most relevant mass flowrate range regarding the hydrogen refueling process. At each measuring point, three repeated measurements were taken. The error (%) is defined as the relative difference between the measurement results of the Coriolis mass flowmeter installed upstream for the pressurized condition and for the other Coriolis mass flowmeter installed downstream of the two pressure regulators. The Coriolis mass flowmeter installed at the downstream location was used as the reference meter, given its traceability to the KRISS National Water Flow Standard System. The error of the Coriolis mass flowmeter was within \(\pm\)0.10% at flowrates from 1.0 kg/min to 5.0 kg/min, and the average error was \(\pm\)0.10% The repeatability of three measurements at each flowrate was less than \(\pm\)0.04%. Figure 7: Measurement results of Coriolis mass flowmeters with the density-matching approach. Figure 9 shows the test results of the Coriolis mass flowmeter when the inlet pressure of the water supplied to the flowmeter was set to 100 bar. The condition of the inlet pressure was increased and controlled by a high-pressure liquid pump and pressure regulators at flowrates of 1.0 kg/min to 5.0 kg/min. In the comparison between the measurement results at 2 bar and 100 bar for the inlet pressure of the water supplied to the Coriolis mass flowmeter, no pressure dependence could be identified. It is interesting to note that when the inlet pressure to the Coriolis mass flowmeter was increased up to 100 bar, the calibration results of the flowmeter were similar to calibration results found by the manufacturer at ambient pressures with water. Figure 8: Measurement results of the Coriolis mass flowmeter at the inlet pressure condition of 2 bar for the pressure-matching approach. Figure 9: Measurement results of the Coriolis mass flowmeter at the inlet pressure condition of 2 bar and 100 bar. Figure 10 shows the measurement results of the Coriolis mass flowmeter when the inlet pressure of the water supplied to the flowmeter was 700 bar, equivalent to the operating pressure conditions at hydrogen refueling stations. The measurement characteristics of the Coriolis mass flowmeter for the pressure-matching approach were investigated in a pressure range of 2 bar to 700 bar at flowrates in the range of 1.0 kg/min to 5.0 kg/min. The error of the Coriolis mass flowmeter was within \(\pm\)0.10% at flowrates from 1.0 kg/min to 5.0 kg/min, and the average error was \(\pm\)0.10%. The measurement results of the Coriolis mass flowmeter for the pressure-matching approach show no detectable dependence of the pressure on the accuracy of measurement performance in the pressure range of 2 bar to 700 bar.