## 3 Results  
For the testing activities, the closed impellers were fitted into an in-house test bench that was designed to test and evaluate the hydraulic performance of the pumps, developed by COMOTI. The test bench allowed temperature control on the pump support and on the working fluid (both under vacuum conditions). The effective integration into the bench was performed with a dedicated pump demonstrator, a modular mechanical assembly that is capable of accommodating numerous geometries by using adapters. The test bench is presented in Figure 13. A National Instruments data acquisition system (DAQ) was used with LabView 2020 software for data interpretation. The DAQ was set to 10 parameters/s data recording. Pressure data were recorded from 13 sensors installed on the pump casing. According to the requirements defined in Table 1, one working point was chosen at 885 kg/h with 11,200 rot/min (2.3 bar pressure rise), and one contingency point at 860 kg/h with 12,000 rot/min (2.65 bar pressure rise). It should be noted that due to the high price and low availability of the HFE7200 working liquid, similitude testing was performed using deionized water. Thus, the two points previously mentioned were a 1.6 bar pressure rise and 620 kg/h for the nominal working point (885 kg/h with HFE) and, respectively, a 1.85 bar pressure rise and 600 kg/h for the contingency point (860 kg/h with HFE). The two working fluids were similar, namely, both are used in thermal control applications for manned spacecrafts. The only aspects that differed were the density, vapor pressure, and specific heat. Before the test run, each closed impeller was operated at lower speeds (800 rot/min, 1200 rot/min, and 2000 rot/min) to observe if there were any vibrations or distinctive sounds specific to unbalance, this being a method of validation for the balancing operations performed. The plots containing the hydraulic performance of each closed impeller were generated using values calculated at stationary operating points for each configuration under test. Each plot contained pressure rise, torque, hydraulic efficiency, and power as a function of flow rate. Due to the large amount of data, Figure 14 presents the mass flow as a function of pressure rise. It can be seen from Figure 14 that the aluminum AM closed impeller achieved lower performance compared to the other closed impellers (the red line in Figure 14), as the remaining closed impellers showed similar results. In order to better highlight the differences between the closed impellers, bar-chart-type graphs were created for the differences  
Figure 13: In-house test bench. in pressure rise and hydraulic efficiency, using the performance of the centrifugal closed impeller made by classical manufacturing as a reference. Values were considered only for the 11,200 rot/min working point. The smallest differences in efficiency were obtained for the titanium alloy closed impeller. Thus, at the flow corresponding to the nominal working point, a very small difference (0.03%) was observed. Instead, the biggest differences were reported within the Inconel 625 alloy closed impeller, as indicated in Figure 15. One important note is that, as presented in Table 2, regarding the efficiency of the AM titanium closed impeller, the efficiency of the contingency point was higher than in the classically manufactured one. In terms of the pressure rise difference, the largest differences were reported for the aluminum AM closed impeller. At low flow rates, the difference in pressure rise in the case of the aluminum closed impeller reached about 5% and decreased with the increasing flow rate.