Radiative properties of alumina/aluminum particles and influence on radiative heat transfer in solid rocket motor

The thermal radiation of micron-sized condensed phase particles plays a dominant role during the heat transfer process in aluminized Solid Rocket Motors (SRMs). Open research mainly focuses on the radiative properties of alumina particles while the study considering the presence of aluminum is lacking. In addition, the thermal radiation inside the SRM with consideration of the participating particles is seldom studied. In this work, the multiscale method of predicting the thermal environment inside SRMs is established from the particle radiation at microscale to the two-phase flow and heat transfer at macroscale. The effective gray radiative properties of individual particles (alumina, aluminum, and hybrid alumina/aluminum) and particles cloud are investigated with the Mie theory and approximate method. Then a numerical method for predicting the thermal environment inside SRMs with considering particle radiation is established and applied in a subscale motor. The convective and radiative heat flux distributions along inner wall of motor are obtained, and it is found that the heat transfer in the combustion chamber is dominated by thermal radiation and the radiative heat flux is essentially a constant of 5.6–6.8 MW/m². The convective heat transfer plays a dominant role in the nozzle and the heat flux reaches the maximum value of 11.2 MW/m² near the throat. As the combustion efficiency of aluminum drops, the radiative heat flux remains unchanged in most regions and increases slightly along the diverging section wall of the nozzle.