Sheath models for thermionically cooled surfaces in two-temperature plasmas

Electron transpiration cooling (ETC) is a proposed thermal management technique for the leading edges of hypersonic vehicles. This technique leverages the well-understood property of thermionically emitted electrons by carrying away heat energy at the surface as potential and kinetic energy. Computational fluid dynamics (CFD) modeling approaches for this phenomenon have developed emissive boundary conditions for ETC. These account for space-charge-limited emission to accurately determine the level of electron emission from the surface. However, CFD modeling approaches for ETC have only considered the thermionic emission from a negatively biased surface. In reality, emitted electrons are expected to travel downstream of the emission point and reattach to the vehicle surface and re-deposit their energy. In this work, we propose an approach to model electron absorption downstream of the thermionic emitter at a positively biased surface. Physics of an electron sheath near a positively biased anode in a 2-T quasineutral plasma are investigated and electron absorption treatment is discussed. Comparison of CFD prediction of the reabsorption model to an ETC experimental investigation is underway.