Computational fluid dynamic model of electron transpiration cooling in weakly ionized air flows

Cesium seeding for effective electron transpiration cooling in hypersonic flows

“…where ρ ∞ and V ∞ are the freestream density and velocity, and r c = 1 cm is the radius of the curvature of the leading edge, taken to be the same as in hypersonic simulations in reference [8]. Calculating the radiative heat transfer from the plasma to the surface, Q p rad , usually requires estimation of various parameters, such as the ionized and excited particle densities, photoionization cross-sections, etc.…”

“…where σ is the Stefan-Boltzmann constant, L is the Rosseland free path, estimated as 4 μm for the cesium plasma at T = 5000 K and ∇T ∼ (T − T s )/L , where L = 0.005 m is taken from [8]. In the limit of black body radiation, the emissivity of plasma, p , is taken as 1.…”

“…At higher coverages, the work function increases due to formation of tungsten oxides. Hypersonic simulations in reference [8] give an oxygen (O and O 2 ) number density of 10 21 m −3 . This means that tungsten surface is exposed to a high flux of oxygen atoms and molecules, but the formation of a monolayer of oxygen is expected to be impeded by the fact that beyond θ = 0.25 and assuming that each oxygen atoms holds three cesium atoms, no lattice sites will be available for adsorption.…”

“…An alternative approach of electron transpiration cooling (ETC) is being actively investigated in the current literature [6][7][8][9][10]. It includes coating of the leading edge surface with a low work-function material, which thermionically emits electrons at high surface temperatures.…”