Electron transpiration circuits for hypersonic leading edges

Abstract

Electron transpiration cooling (ETC) is a candidate thermal management approach for the leading edges of hypersonic vehicles. This approach transforms thermal energy at a heated surface, such as a hypersonic leading edge, into electrical energy via thermionic emission. Downstream of the leading edge, electrons from both the emission point and the ionized flowfield can be collected and fed back to the emission point, completing the ETC circuit. While computational fluid dynamics boundary conditions for ETC have been developed, they have only considered the emissive surface. In this work, we describe a model for a complete ETC system (i.e., emissive and collective surfaces with internal circuitry), incorporating kinetically informed modifications to classical sheath theory and detailed sheath heating expressions. A parametric analysis of the ETC circuit is performed in the context of a two-species bulk plasma with a collisionless sheath, and the role of the collecting surface is established. Cooling and efficiency metrics of the ETC system are constructed, and operating conditions to maximize cooling and efficiency are identified. The ETC system is found to offer cooling performance in a hypersonic environment, with some configurations even allowing for the generation of power. Finally, the performance of the ETC circuit model is compared to experimental measurements where reasonable agreement is observed.