## 3 Results and Discussion
### Dynamic Response Characteristics of the Heat Pipe Systems  
Figure 5 demonstrated the surface temperature distribution of TSHP-1 after reaching the threshold critical power with different heat load B, including (a) 2 W and (b) 4 W. As shown in Figure 5a, TSHP-1 was under normal working before 700 s for the tested points T1-T9 remained relatively stable. TSHP-1 then came into overload working status with the increased heat load A after 700 s. It could be seen that the surface temperature of T1 increased quite rapidly, which meant that the evaporation section was dried-out. However, the surface temperature of T1 recovered stability with heat load B input of 2 W after 1000 s. The stable status of TSHP with heat load B input of 2 W remained at approximately 250 s, and then the surface temperature of T1 increased rapidly to cause the dry-out status of TSHP-1. The stable status of TSHP recovered after heat load B input of 4 W, as shown in Figure 5b. The surface temperature of T8 and T9 grew up when heat load B was input, while that of T1 decreased to the original state. Moreover, the surface temperature of the tested points was kept stable, which meant that the whole heat pipe system could maintain stability after heat load B input of 4 W. The surface temperature distribution of TGHP-1 after reaching the threshold critical power with different heat load B is shown in Figure 6. The changing situation of TGHP-1, which recovered from the dry-out status to the stable status, was almost the same as that of TSHP-1. However, the minimum heat load B input of TGHP-1 was quite different from that of TSHP-1. When heat load B input was 4 W, TSHP-1 could be recovered to the stable status, while TGHP-1 would be recovered stable when heat load B input was at least 6 W.  
Figure 4: The distribution of steam pressure inside the heat pipes: (a) the distribution of steam pressure inside the heat pipes with only one single heat load; (b) the distribution of steam pressure inside the heat pipes with two heat loads (one heat load for the heat source, and the others served as a thermal switch). From the above, it could be known that the heat pipe system would recover from the dry-out status to the stable status with a proper heat load B input. Furthermore, the recovery characteristics of TSHP-1 with heat load B input of 10 W after the surface temperature of T1 dried out to different temperatures, including 75 \({}^{\circ}\)C and 94 \({}^{\circ}\)C. As shown in Figure 7a, the recovery time of TSHP-1 after being dried out was quite short (less than 150 s) with heat load B input when the surface temperature of T1 was 75 \({}^{\circ}\)C. It meant that the addition of heat load B played a significant role in adjusting the status switching of TSHP-1. Moreover, TSHP-1 recovered rapidly when the surface temperature of T1 was low. Therefore, TSHP-1 recovered to a stable status quite rapidly when the evaporation section was under the dry-out status for a short time. On the contrary, TSHP-1 recovered quite slowly because the surface temperature of T1 was high. It also meant that TSHP-1 was out of stable status for a long time. As a result, nearly 450 s was paid for the status recovery of TSHP-1 in Figure 7b. The reason for the different recovery times of TSHP-1 with a different surface temperature of T1 may be that TSHP-1 under the dry-out status with different times caused different  
Figure 5: The surface temperature distribution of TSHP-1 after exceeding the threshold critical power (heat load A was 65 W) with different heat load B, including (**a**) 2 W and (**b**) 4 W.  
Figure 6: The surface temperature distribution of TGHP-1 after exceeding the threshold critical power (heat load A was 65 W) with different heat load B, including (**a**) 2 W, (**b**) 4 W, and (**c**) 6 W.  
pressure distribution in the heat pipe, and it would greatly influence the rebuilding time of the stable status in the heat pipe because the imbalance pressure distribution of the heat pipe changed with time under the dry-out status.