*2.3. Measurement of Geometric Parameters*

To verify the accuracy of the geometric model, it was necessary to measure, for each pump subject of this analysis, the following geometric parameters:


The measurement of some of the parameters listed above such as the diameters and the height of the blades did not present difficulties. To perform such measurements, a vernier caliper was used (0–1000 mm range, 0.15 mm accuracy). The evaluation of the angles *β*<sup>1</sup> and *β*<sup>2</sup> was carried out adopting the following methodology:


$$r = a \; e^{m\theta} \tag{48}$$

Having a series of pairs of values of *r*, *θ* it is possible to evaluate by interpolation the unknown values *a* and *m* of Equation (47). To obtain the values *r* and *θ*, the various measured impellers were mounted on a divider disc of the type used for milling machines. This disc allowed the rotation of the impeller installed on it exactly by the desired angle, with great precision.

