## 3 Results and Discussion
This includes (**a**) relationships pertaining to the three types of entropy production, where losses in the form of head are observed in Impeller 2 while operating with the original RGV; (**b**) relationships related to the three types of entropy production, where losses in the form of the head are observed in Radial diffuser 1 while operating with the original RGV; (**c**) relationships related to the three types of entropy production, where losses in the form of head are observed in Impeller 2 while operating with RGV1; (**d**) relationships related to the three types of entropy production, where losses in the form of the head are observed in Radial diffuser 1 while operating with RGV1; (**e**) relationships related to the three types of entropy production, where losses in the form of head are observed in Impeller 2 while operating with the form of head are observed in Impeller 2 while operating with RGV2; (**f**) relationships related to the three types of entropy production, where losses in the form of head are observed in Radial diffuser 1 while operating with RGV2. The analysis of the graphs clearly indicates that in all cases, the losses h\({}_{\text{v,T}}\), h\({}_{\text{v,V}}\) and h\({}_{\text{v,W}}\) have similar values when the pump is operating with the original RGV and RGV2, which holds true for the entire range of flow rate studied. The loss values when operating with RGV1 fluctuate between those of RGV2 and the original RGV. Losses h\({}_{\text{v,T}}\) obtained  
Figure 8: Relative losses in the Impeller and Radial diffuser 1 obtained as a result of entropy production. This includes (**a**) the relationships concerning the losses h\({}_{\text{v,T}}\), presented as head losses obtained in Impeller 2 when operating with the three types of RGV; (**b**) the relationships concerning the losses h\({}_{\text{v,T}}\), presented as head losses obtained in Radial diffuser 1 when operating with the three types of RGV; (**c**) the relationships concerning the losses h\({}_{\text{v,V}}\), presented as head losses obtained in Impeller 2 when operating with the three types of RGV; (**d**) the relationships concerning the losses h\({}_{\text{v,V}}\), presented as head losses obtained in Radial diffuser 1 when operating with the three types of RGV; (**e**) the relationships concerning the losses h\({}_{\text{v,W}}\), presented as head losses obtained in Impeller 2 when operating with the three types of RGV; (**f**) the relationships concerning the losses h\({}_{\text{v,W}}\), presented as head losses obtained in Radial diffuser 1 when operating with the three types of RGV. in the pump impeller predominate when operating with RGV1, while losses h\({}_{\text{v,v}}\) in the diffuser predominate when operating with RGV. When using the diffuser, the individual types of losses are similar when operating with the three studied vanes. Analyzing the previous statements leads to the conclusion that the shape (design) of the studied vanes does not have a significant impact on the losses in the pump stage, as well as on its hydraulic coefficient of efficiency. In order to clarify the reason for the increased head when operating with vanes RGV1 and RGV2, the impact of RGV on the velocity field in front of Impeller 2, and thus on the theoretical head H\({}_{\text{t}}\), is studied. To achieve the main purposes of this study, the theoretical head H\({}_{\text{t}}\) and the head of Impeller 2 H\({}_{\text{imp}}\) are determined by applying the following equations:  
\[\rm H_{rel} =\frac{H_{i}}{H_{n}}\]0  
where \(\overline{\text{u}_{1}\text{c}_{\text{u1}}}\) and \(\overline{\text{u}_{2}\text{c}_{\text{u2}}}\) are mass flow averaged values, obtained by using the relative velocity \(\text{u}=\text{r}\omega\) and the relevant component of the absolute velocity c\({}_{\text{u}}\) (circumferential velocity) at the entrance (subscript 1) and at the impeller output (subscript 2); \(\omega\) (rad/s) is the impeller angular velocity; r is the radius at the inlet and Outlet of the impeller; g is gravity acceleration.