Heat-transfer characteristics of CO[formula omitted] boiling flow in the regenerative cooling channel of an Mg/CO[formula omitted] powder rocket engine for Mars missions.

To solve the problem of thermal protection posed by the long working time of Mg/CO 2 powder rocket engines, an experimental system is designed to study the heat-transfer characteristics of liquid CO 2 in the regenerative cooling channel. How the heat flux, coolant temperature, mass flux, and back pressure influence the heat-transfer coefficient, the thermodynamic quality, and the gas-phase formation point of nearly saturated CO 2 is studied. The heat-transfer coefficient is found to increase with increasing mass flux or decreasing inlet temperature. Higher heat flux increases the rate of bubble formation and promotes nucleate-boiling heat transfer, but it also intensifies the film boiling, thereby degrading the heat-transfer performance. Lower back pressure does not affect the heat-transfer performance in the nucleate-boiling region, but it worsens it in the film-boiling region. It is also found that the classical boiling-heat-transfer models do not predict the experimental heat-transfer coefficient well. Combined with experimental data, how reduced pressure affects heat transfer is considered, and a new empirical correlation formula is proposed for the heat-transfer coefficient of CO 2 near saturation. The optimized model can successfully predict 90.23% of the experimental data, and the prediction accuracy is improved greatly. The present research provides a theoretical basis for designing a regenerative cooling scheme for an Mg/CO 2 powder rocket engine. • Liquid CO 2 is used as coolant for the first time to conduct heat transfer experiments in a regenerative cooling channel. • A method for calculating the heat transfer coefficient along the microchannel is established. • The effects of different heat fluxes, coolant temperatures, mass fluxes and back pressures on the heat transfer performance of CO 2 are obtained. • An empirical correlation for heat transfer of CO 2 boiling flow in a regenerative cooling channel at near saturation state is obtained. [ABSTRACT FROM AUTHOR]