## 3 Results and Discussion
### Thermal Management Experiment
#### 3.2.1 Heating Run
This can be explained by the fact that for longer operation times, the PCMs get completely melted (retains no latent heat) therefore temperature curves for HS only and HS with PCMs come closer which is evident in Figure 5C. Figure 6A shows that, under FV for 5 min, the device temperature can be maintained below safety limit by HS only (Ref-FV) up to 8 W; however, addition of PCMs (salt-FV, paraffin-FV and Milk fat-FV) extended it to 10 W. PCMs rendered an additional temperature drop as compared to HS only under FV. In comparing PCMs' performance, milk fat performed better than the other two PCMs from 4 W to 8 W, but the trend reversed at 10 W.  
Figure 5: Average heat sink base surface temperature (\(T_{b}\)) for three PCMs at 4–10 W heat loads under NV for: (**A**) 5 min; (**B**) 15 min; and (**C**) 60 min. Figure 6: Average heat sink base surface temperature (\(T_{b}\)) for three PCMs at 4–10 W heat loads under FV for: (**A**) 5 min; (**B**) 15 min; and (**C**) 60 min at heat loads. Figure 6B shows that for a longer operation time of 15 min, HS only under FV can maintain the device below safety temperature up to 6 W. The inclusion of PCM extends service to higher heat loads of 8 W for all PCMs and 10 W in the case of salt hydrate. For a 15 min period, salt hydrate performs better than the other PCMs. Figure 6C shows that for a prolonged operation of 1 h, the HS-only under FV maintains the device under safety temperature at a lower heat input of 4 W while adding PCMs can extend it to 6 W. At heat loads above 8 W, the device temperature will exceed safety limit and hence will be prone to failures. It can be emphasized that at higher heat loads additional measures would be needed, e.g., increasing the amount of PCM, increasing thermal conductivity of PCMs, improving contact resistance between HS and heat generator and increasing ventilation rates. Figure 7 summarizes the optimum cooling techniques as a function of operation time and heat loads. In order to compare the PCM cooling performance over the whole duration of experiments, average temperature drop (ATD) achieved by each PCM is presented in Figure 8 at 4-10 W heat loads under NV and FV. In the case of NV, using salt hydrate (red bars) achieved the highest ATD value (15 \({}^{\circ}\)C) due to higher \(\rho\), \(K\) and \(L\), while milk fat (milk fat-NV) showed lowest ATD (7-8 \({}^{\circ}\)C) at all tested heat loads. In the case of FV, the salt hydrate achieved the highest ATD reaching up to 33 \({}^{\circ}\)C at heat loads of 10 W (9748 W/m\({}^{2}\)) compared to the other two PCMs. However, at 4 W heat load, milk fat achieved a slightly higher ATD (19 \({}^{\circ}\)C) compared to salt hydrate (17 \({}^{\circ}\)C) while the paraffin showed the lowest ATD (13 \({}^{\circ}\)C). Figure 8: Average temperature difference (ATD) at the HS surface for the operational modes compared to the reference for different PCMs (salt hydrate, paraffin and milk fat subjected to: (**A**) NV; and (**B**) FV at heat power input of (4 W, 6 W, 8 W and 10 W). Figure 7: The optimum cooling techniques depending on operation time and heat load.