## 4 The Experimental Campaign
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Parameter** & **Steady State** & \multicolumn{4}{c}{**Partial LOFA Runs**} & \multicolumn{2}{c}{**Full LOFA**} \\ \hline Valve V-1 opening (\%) & 100 & 60 & 40 & 20 & 10 & 5 & 0 \\ Valve V-2 opening (\%) & 0 & 34 & 44 & 54 & 63 & 64 & 67 \\ LOFA duration (s) & - & 120 & 120 & 23 & 12 & 6 & 3 \\ \hline Flow meter 1 (g/s) & 300 & 170 & 150 & 90 & 64 & 56 & 43 \\ Flow meter 2 (g/s) & 350 & 350 & 350 & 350 & 350 & 350 & 350 \\ \hline Max. outlet temp. (\({}^{\circ}\)C) & 323 & 334 & 337 & 346 & 344 & 342 & 338 \\ MAwg. pressure drop—Circuit 1 (mbar) & 2935 & 970 & 760 & 260 & 150 & 110 & 65 \\ Avg. pressure drop—Circuit 2 (mbar) & 3550 & 3550 & 3550 & 3550 & 3550 & 3550 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Second batch of tests performed at 330 kW/m\({}^{2}\). shows a tendency to settle oppositely to the other two cases (10% in Figure 18b) and 5% in Figure 18c) where the evolution was almost linear for the recorded time. Figure 16: Experimental tests execution example (300 kW/m\({}^{2}\) heat load). Figure 17: Outlet coolant temperature from channels 3 and 4 at a heat flux of 300 kW/m\({}^{2}\) averaged over all similar runs at: (**a**) 60% valve opening; (**b**) 40% valve opening. The indicated uncertainties are total uncertainties, which are varying between 2 and 2.9 \({}^{\circ}\)C.  
From the three pictures in Figure 18 it can be seen that the time for which the valve V-1 was maintained at reduced opening was decreased from 30 s in the case of a 20% opening to only 20 s for the 10% and 5% cases. The reason for this is that the simulated LOFA event was terminated (V-1 reopens) once the IR camera measured temperatures over 550 \({}^{\circ}\)C on the mock-up surface. Since the transient duration was shorter, the temperature field was not fully established and, while locally, the temperature reaches 550 \({}^{\circ}\)C rather quickly, there are regions that have a lower temperature increase rate. This non-uniform heating rate is the explanation why, for the temperatures plotted in Figure 15b, the recorded temperature values in the region Ch 3_20 showed a tendency towards decreasing in their maxima with respect to the valve V-1 opening. The \"total LOFA\" case, namely the one where the valve V-1 set point was set to 0% showed some distinct features as compared with the others. First of all, it should be mentioned that, even if the set-point was zero, the flow rate through the channels 1 to 5 dropped only to about 30 g/s (6 g/s per channel in average), as can be seen in Figure 16. The reason for this is that, at the lower end (<1%) of the valve opening, the valve actuator cannot follow the imposed closing ramp of 10%/s. It actually takes a bit longer than 1 s to fully close the last few % down to 0. Since the temperature on the mock-up was rising very quickly, it was not possible to keep the valve at 0% long enough for the flow through the sensor to drop to 0. In addition to that, the flow meter systematic uncertainty at these small flow rates is high, so the actual flow rate could have been lower. The typical coolant temperature evolution at the outlet of channels 3 and 4 in a 0% scenario (300 kW/m\({}^{2}\)) is shown in Figure 19. As can be seen the outlet temperature increased in both channels, but between 16 s and 20 s it remained in quasi-steady conditions. Then, it increased again, peaking at 342 \({}^{\circ}\)C in channel 3 and 337 \({}^{\circ}\)C in channel 4. After 23 s the temperature decreased again because a sufficient mass flow rate is re-established through the channels. The quasi-steady temperature between 16 and 20 s is probably due to small backflows occurring in these channels. Actually, the coolant in the outlet manifold is colder than that in the outlet of channels 3 and 4, being the result of the mixing of the coolant also coming from the unheated channels (channels 1, 2, and 5). This colder coolant mixes with the residual coolant crossing the channels, showing this peculiar plateau.