A Transpiration- Cooled Nozzle as Applied to a Gas-Core Nuclear Propulsion System

The use of mass injection through a porous wall as a cooling technique for axisymmetric nozzles is investigated. The effect of homogeneous mass injection on the heat transfer in a turbulent, compressible boundary layer is analyzed, using an integral-momentum approach. Approximate formulations of the gaseous thermal radiative and recombination energy contributions are included in the analysis. Coolant requirements are determined for a conical nozzle associated with a 106 Ib-thrust gas-core system operating at a 300-atm chamber pressure. Hydrogen is assumed to be used for the propellant and coolant. Chamber temperatures range from 7500° to 20,000°R, and wall temperatures range from 2000° to 3000°R. The degradation of specific impulse, which is a result of expelling the coolant at a lower total temperature than that in the chamber, is found to be as high as 9% at 20,000°R for a wall temperature of 2000°R.