JM
J. Maszkowski
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Non-equilibrium Fluid Model for Expander
Development of a Two-Phase, Non-equilibrium Fluid Model for System-level Simulation of an Expander for Hydrogen Fuel Cell Propulsion Systems
To reduce the impact of aviation on climate, more sustainable propulsion systems need to be developed. One proposed solution is the hydrogen fuel cell. This propulsion system requires pressurized air for optimal operation. The energy of this air can be utilized by a radial expander located downstream of the fuel cell, which transfers mechanical power to the compressor. Accurate estimation of expander parameters and design is crucial for efficient propulsion system development. Although current fluid models cover a wide range of compositions and flow regimes, there is still a need for a system-level fluid model that accounts for non-equilibrium condensation optimized for expanders. The goal of this study is to explore the consequences of considering or neglecting non-equilibrium condensation on expander performance and design. The developed fluid model is a hybrid approach combining NASA polynomials for species-specific property estimation, IF97 for dew point prediction, and a surrogate model for subcooling temperature calculation. To enable a fair comparison between equilibrium and non equilibrium condensation, a simplified one-dimensional expander model was also developed. The comparison results show that considering non-equilibrium condensation increases the projected power and mass flow while decreasing the cross-sectional area of the expander at the outlet for given inlet and design conditions. The specific work remains unchanged; however, the values of thermodynamic properties along the normalized streamwise location differ when non-equilibrium condensation is considered. The most significant differences include lower static temperature, higher density, and increased water vapor content. It is concluded that such discrepancies should be included in system-level simulations to improve propulsion system mass and efficiency. Moreover, the effects of composition changes under non-equilibrium conditions show that expander performance strongly depends on the water content, the amount of condensation, and the magnitude of subcooling. Higher water content decreases mass flow while increasing specific work and power of the expander; however, it reduces total-to-total efficiency because of increased condensation. Future work should focus on expanding the surrogate model to cover a wider range of pressure ratios in order to improve the accuracy of subcooling temperature prediction. Additionally, the fluid model could be extended to include more thermodynamic and transport properties required for more sophisticated expander models.
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To reduce the impact of aviation on climate, more sustainable propulsion systems need to be developed. One proposed solution is the hydrogen fuel cell. This propulsion system requires pressurized air for optimal operation. The energy of this air can be utilized by a radial expander located downstream of the fuel cell, which transfers mechanical power to the compressor. Accurate estimation of expander parameters and design is crucial for efficient propulsion system development. Although current fluid models cover a wide range of compositions and flow regimes, there is still a need for a system-level fluid model that accounts for non-equilibrium condensation optimized for expanders. The goal of this study is to explore the consequences of considering or neglecting non-equilibrium condensation on expander performance and design. The developed fluid model is a hybrid approach combining NASA polynomials for species-specific property estimation, IF97 for dew point prediction, and a surrogate model for subcooling temperature calculation. To enable a fair comparison between equilibrium and non equilibrium condensation, a simplified one-dimensional expander model was also developed. The comparison results show that considering non-equilibrium condensation increases the projected power and mass flow while decreasing the cross-sectional area of the expander at the outlet for given inlet and design conditions. The specific work remains unchanged; however, the values of thermodynamic properties along the normalized streamwise location differ when non-equilibrium condensation is considered. The most significant differences include lower static temperature, higher density, and increased water vapor content. It is concluded that such discrepancies should be included in system-level simulations to improve propulsion system mass and efficiency. Moreover, the effects of composition changes under non-equilibrium conditions show that expander performance strongly depends on the water content, the amount of condensation, and the magnitude of subcooling. Higher water content decreases mass flow while increasing specific work and power of the expander; however, it reduces total-to-total efficiency because of increased condensation. Future work should focus on expanding the surrogate model to cover a wider range of pressure ratios in order to improve the accuracy of subcooling temperature prediction. Additionally, the fluid model could be extended to include more thermodynamic and transport properties required for more sophisticated expander models.