## 5 Discussion  
Loop heat pipes are commonly analysed using various analytical models, including steady-state and transient models. In this study, we presented the lumped parameter model which exhibits thermal performance comparable to that reported by other researchers [33], indicating its reliability. It is worth noting that different authors may adopt distinct modelling approaches, highlighting specific elements of the loop heat pipe or incorporating additional components like radiators in the condenser line with sub-cooling effects, as discussed in [24]. The primary objective of this article was to simulate the heat switch effect that occurs during loop heat pipe dry-out. To achieve this, the model required adjustment parameters. For instance, we set \(h_{CC}\) to a value of 50 (W/(m\({}^{2\circ}\)C)), resulting in a thermal conductance of \(G_{CC}\) = 0.267 (W/\({}^{\circ}\)C), ensuring reliable behaviour of the condenser. However, it is crucial to correlate this value with dedicated experimental data to enhance the model accuracy in order to find the correct thermal conductance coefficient \(h_{CC}\) due to convective effects. Figure 8: Chart with changing in differential pressure (\(\Delta P=P_{6-7}-P_{4-5}\)) and heating/cooling loads (\(\dot{Q}_{cusp}\) and \(\dot{Q}_{CC}\)) over time. Figure 7: Chart with changing in liquid masses in condenser, compensation chamber and wick (\(M_{4-5}\), \(M_{6-7}\) and \(M_{7-1}\)), and heating/cooling loads (\(\dot{Q}_{cusp}\) and \(\dot{Q}_{CC}\)) over time. Additionally, the investigation of the convection coefficient between the vapour and condenser lines (\(G_{(3-4)-ext}\)) is another important aspect that required adjustments to achieve a closer fit between the test data curve from [33] and our model. During the development of this lumped parameter model, another interesting finding emerged, which highlighted the criticality of correction coefficients, namely \(f_{m1}\) and \(fG_{1-(1-2)}\), to simulate the five operational states of the loop heat pipe. Similar to \(f_{\epsilon}\), as suggested in [22; 23], these correction factors account for the influence of Wick dry-out. Interpreting these results in light of previous studies and working hypotheses, it is evident that the lumped parameter model demonstrates thermal performance consistent with that in the established literature, validating its efficacy as a modelling approach for studying the heat switch effect during loop heat pipe dry-out. However, further investigation is warranted to refine and validate the model by comparing it with experimental data and exploring the convection coefficient between the vapour and condenser lines (\(G_{(3-4)-ext}\)) in greater detail. An intriguing discovery emerged during the analysis of simulated results, as illustrated in Figures 6-8. This discovery relates to the connection between the startup event, occurring at \(Time=1.1\) h, and the cooling process (\(Q_{CC}\)) within the time frame of 1 to 1.2 h, specifically at the compensation chamber. In these figures (Figures 6-8), a significant observation is that \(T_{8}\) initiates cooling before the compensation chamber completes its cooling phase, which concludes at 1.2 h. This phenomenon can be attributed to the negative pressure differential (\(\Delta P\)) between the compensation chamber (\(P_{6-7}\)) and the condenser (\(P_{4-5}=P_{3-4}\)), defined as \(\Delta P=P_{6-7}-P_{4-5}<0\)Pa, as observed in Figure 8. This pressure differential plays a crucial role in facilitating the inflow of liquid into the compensation chamber (\(M_{6-7}\)) and the Wick (\(M_{7-1}\)), as depicted in Figure 8 at 1.1 h, enabling the device to restart. This means that the start-up of the device could be achieved even with reduction in cooling power (\(Q_{CC}\)) or its time frame. Given the transient nature of heat switch thermal simulations, a transient model proves to be a valuable tool, facilitating dimensioning and allowing for the determination of the appropriate amount of heating or cooling power and the respective application period.