In this work, we numerically investigated the heat transfer effectiveness of different phase change materials (PCMs) when infused in a plate-fin heat sink with a fixed volume fraction of thermal conductivity enhancer. The PCM's ability to absorb and release large amounts of thermal energy at constant temperature is a desired feature in transient electronics cooling applications. In this study, we focused on examining the effect of the number of fins, type of PCM, heat flux, PCM volume fraction, and heat sink bottom wall thickness. The results showed that increasing the number of fins improved the performance of the PCM-infused heat sink. When a heat flux of 4000 W/m² was applied for 30 minutes on a plate-fin heat sink infused with paraffin wax, the maximum temperature did not exceed 70°C in the four-fin design, while it exceeded 80°C in the two-fin design. A salt hydrate PCM outperformed paraffin wax and RT35. The bottom wall of the heat sink acted as a thermal spreader and a nonlinear relationship existed between the bottom wall thickness and the maximum electronics temperature. Compared to the two- and four-fin heat sink models, the zero-fin model required the longest time to fully melt the entire PCM due to the additional amount of PCM present in the heat sink gaps.

This study provides a step-by-step, up-to-date fuel cell fundamentals, thermodynamic and electrochemical principles, and system evaluation factors via a case study of a 10-kW alkaline fuel cell designed to operate in space applications. The system also produces 100 kg of pure water and 5.5 kW of heat. The system is modelled using MATLAB and ANSYS Fluent. Then, the model is verified with theoretical and experimental results from the literature. A parametric study of various design and operating parameters, and material selection is carried out to optimize the overall performance. A net output voltage of 0.8 V is obtained at 150 mAcm-2 current density, which yields an overall efficiency of 75%. The results indicate that increasing the electrolyte thickness or operating temperature results in a lower net voltage output. Additionally, improving the performance of a fuel cell through the bipolar plate can be achieved by understanding the contribution of different parameters towards minimizing the pressure drop across the bipolar plate. It is found that implementing an optimized selection of fluid flow rate, channel width, channel depth, number of channels and current density minimize the pressure drop throughout the bipolar plate. Relative humidity has a significant effect on the pressure drop. Results indicate that increasing the relative humidity consequentially rises the pressure drop. Finally, the CFD simulation illustrates that the end-zones in the bipolar plate accumulates fluid due to the nature of stagnation at those locations. Thus, total pressure at those locations is the highest. One of the major contributions here is studying the effect of KOH concentration on the performance of the AFC at different operating temperatures. In addition, a wide range of design and operating parameters were analysed to understand their effect on the overall performance of the fuel cell.