Numerical Analysis of Deterioration in Heat Transfer to Near-Critical Rocket Propellants

Abstract

Liquid propellants, which are typically used for regenerative cooling of rocket thrust chambers, can flow in channels at supercritical pressures and in the neighborhood of pseudocritical temperature (near-critical fluid). This could be for instance the case for the envisioned liquid-oxygen/liquid-methane engines with chamber pressures larger than about 50 bar. When the fluid is in such a near-critical condition, deterioration in heat transfer can occur if the heat transfer level is higher than a threshold value. Aiming to improve flow prediction capabilities for the design of such systems, the present study is devoted to numerical simulations of near-critical fluids flowing in uniformly heated straight tubes. After code validation against experimental data of near-critical-hydrogen flow, numerical simulations of near-critical-methane flow in heated tubes are carried out, each characterized by a different wall heat flux. Results are discussed in detail and the near-critical-methane flow condition that exhibits the heat transfer deterioration is identified and emphasized.

The study has been partially supported by ESA/ESTEC under contract no. 21881/08/NL/PA and MIUR (the Italian Ministry of University and Research).

Notes

¹The pseudo-critical temperature is the temperature at which specific heat at constant pressure c _p has a maximum at a specified pressure.

²In analogy with the definition introduced in the field of combustion which identifies a transcritical fluid as a fluid which is injected in the combustion chamber at supercritical pressure and subcritical temperature [3].