An analytical model of heat transfer and fluid dynamic performances of an unconventional NTR engine for manned interplanetary missions

An analytical model of fluid flow and heat transfer of a Nuclear Thermal Rocket (NTR) engine concept is presented. The engine is based on the direct conversion of the kinetic energy of the fission fragments (FFs) into the propellant enthalpy. The FFs can escape from an extremely thin layer of fissionable material: a sufficiently large surface coated with few micrometers of Americium 242m, confined by a neutron moderator–reflector, may become a critical reactor. Three dimensional coupled CFD-Monte Carlo simulations have already been presented in Di Piazza and Mulas (2006). In this paper, an analytical integral 1-D model of fluid dynamics and heat transfer is built in order to foresee the performances on the basis of simple, physically founded correlations. The Peclet number has been identified as the main governing parameter of the system, and theoretically based correlations have been found for the thermodynamic efficiency of the engine and for the specific impulse. The correlations show a good agreement with numerical results presented in Di Piazza and Mulas (2006) from fully coupled 3D CFD-Monte Carlo calculations.