*4.2. Corrected Mass Flow*

In order to compare the measured results to the theory of corrected mass flow calculation, the measurements were corrected with Equations (5) and (7) to 940 mbar(a) and 20 ◦C, as shown in Figure 4. For the speed correction required for varying inlet temperatures, it was necessary to use curves with different speeds than the measured ones. A linear interpolation between 100 and 140 krpm was used to correct the speeds for the 120 krpm curves and a linear interpolation between 120 and 140 krpm was used to correct the 140 krpm curves. In reality, an exponential behavior would be expected, but the error made by using the much simpler linear interpolation was estimated to be below 5%, and thus negligible compared to the measurement error. An interpolation is always necessary if the compressor limits are corrected at lower inlet temperatures. For the 40 ◦C curve, the corrected speed is 145 krpm which would not be possible with the measured compressor.

**Figure 4.** (**a**) Pressure ratio over corrected mass flow for measurements with 940 mbar(a) (black), 700 mbar(a) (light blue) and 500 mbar(a) (dark blue) inlet pressure at 20 ◦C, corrected to 20 ◦C and 940 mbar(a). (**b**) Pressure ratio over corrected mass flow for measurements with −10 ◦C (dark blue), 20 ◦C (black), 5 ◦C (light blue) and 40 ◦C (red) inlet temperature at 940 mbar(a), corrected to 20 ◦C and 940 mbar(a).

The resulting curves matched well within the range of the measurement error. Therefore, it can be concluded that Equations (5) and (7) correctly described the shift of the compressor map for the speed limit, as this is the relevant limit for the observed measurements.
