| Resumo : |
Every day the interest of space agencies and private companies in space exploration increases, mainly in deep space missions. This type of mission poses great challenges due to the high energy level demanded from the power systems, requiring a more efficient and compact energy generation and conversion system. Space electric propulsion systems are seen as the most promising system for deep space missions, covering exploration and colonization missions. For these systems to become viable, they need to have high efficiency associated with low mass. Taking this into account, this work carried out a thermodynamic analysis and exergy analysis of a Stirling cycle for conversion of nuclear energy in space. A heat pipe model was implemented to identify the impact of heat pipes on the cold and hot side on the overall performance of the Stirling engine. Constructive parameters of the Stirling engine, such as regenerator effectiveness, compression ratio, overall thermal conductance of the heat exchangers, motor frequency, piston stroke, and piston area, were varied in order to understand the impact of these parameters on the system. An exergy analysis was conducted to quantify the system irreversibility and the exergy efficiency of each component of the cycle. With the results, it was possible to identify that the regenerator effectiveness, can provide great gains for the engine efficiency, however, very high regenerator effectiveness can reduce the power of the cycle. The compression ratio of the system tends to increase the engine efficiency, but the compression ratio above 6 does not provide considerable gains for the cycle, in comparison to the gains obtained by increasing the ratio up to 6. The component with the greatest irreversibility is the reactor core due to the characteristics of nuclear reactions which, like chemical reactions, are highly irreversible. The second component with the greatest irreversibility is the radiator, and also the component responsible for the highest percentage of the system mass. With the results obtained, the best parameters were implemented providing the system to reach a power of 260 kW and an energy density of 35.38 kg/kW, which is a great result in view of the requirements of its application. Therefore, this study can serve as a guideline for future projects of nuclear Stirling conversion cycle, providing an analysis of the energy quality of the cycle and how the construction parameters impact the overall performance of the system. |