# Engineering Design of the European DEMO HCPB Breeding Blanket Breader Zone Mockup
## 2 Design of the Mockup
### Design Description  
After many iterations between designers and experimentalists, the design has been defined, as shown in Figures 3 and 4, only pending confirmation from manufacturing partner. The mockup is connected to the HELOKA facility by using two flanges, facilitating the exchange of test sections. The mockup is heated through three-coiled, wire-form electric heaters, which are embedded into the grooves on the Tube-1 through brazing to ensure a good contact. The three electric heaters are identical and each can have a maximum heating power of 2000 W. The maximum power needed in this experiment is expected to be about 4000 W. The electric heaters will work at lower than the maximum heating capacity to optimize their lifetime. In order to test the heat transfer enhancement of different roughness conditions on the surface of the annular channel, the mockup is designed in a way to make sure that the Tube-3 is exchangeable. Different roughness profiles were manufactured on the outer surfaces of different versions of Tube-3 that can be consecutively integrated into the mockup. \begin{table}
\begin{tabular}{c c c} \hline \hline \(\mathbf{q^{+}}\) & **Heat Flux in HCPB [W/m\({}^{2}\)]** & **Heat Flux in Mockup [W/m\({}^{2}\)]** \\ \hline
0.0002 & 3.25 \(\times\) 10\({}^{4}\) & 3976 \\ \hline
0.0003 & 5.94 \(\times\) 10\({}^{4}\) & 5971 \\ \hline
0.0004 & 6.69 \(\times\) 10\({}^{4}\) & 7970 \\ \hline
0.0005 & 9.25 \(\times\) 10\({}^{4}\) & 9972 \\ \hline
0.0006 & 1.03 \(\times\) 10\({}^{5}\) & 11,979 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Heat flux comparison at same q\({}^{+}\) of selected Re number. Figure 3: CAD of mockup. Tube-2 acts as the tube carrier for the Tube-1 (for heaters) and Tube-3 (for roughness). There are grooves for the three wire-form electric heaters. After winding into the grooves on Tube-1, the heaters are then brazed with Tube-1 and Tube-2. The Tube-3 is attached to Tube-2 using tack welding, which allows the Tube-3 to be dismantled from the Tube-2. At the upstream region, there is a cover-dome for guiding the coolant to flow into the annular channel formed by Tube-3 and Tube-4. Now, the Tube-1, Tube-2, and Tube-3 are bundled together, thereafter called insert-tubes. The region containing the tubes Tube-1, Tube-2, Tube-3, and Tube-4 is also called the test section. The outer contour of the mockup is driven by the dimension of Tube-4 (DN 150-120), which was determined using the above-mentioned upscaling methods. The Flange-1 is used to connect the mockup to the helium loop, whose pipe size is smaller than Tube-4. Therefore, two reducers are used to connect the Flange-1 to Tube-4. Tube-4 is then connected with a T-junction. The 90\({}^{\circ}\) branch is welded to Pipe-2 for returning the flow to the helium loop (see Figure 4). Again, a reducer (Reducer-3) is used for the transition of differently sized pipes. Between the Reducer-3 and the Flange-4, an elbow is used for accommodating thermal expansion. The straight branch of the T-junction is for facilitating the exchange of the insert-tubes and the feedthroughs of the electric heaters and thermocouples (TCs) through the Flange-2. These feedthroughs are needed for ensuring the tightness of mockup. The insert-tubes are connected by three evenly spaced support rods to a thick circular plate between the Flange-2 and Flange-3. The Flange-2 has an outer diameter of 395 mm. The total horizontal length from the inlet flange (Flange-1) to the end-tip of feedthrough is about 2080 mm. The vertical height of the mockup is about 898 mm. The total mass of this mockup (without considering isolation) is about 362 kg. The insert-tubes, which are planned to be exchanged during the experimental campaign, have a mass of about 67 kg. The nominal dimensions of the 4 tubes at the test section is shown in Table 2. It is desired that, during the manufacturing, a small fabrication tolerance will be maintained.