This paper presents a solid rocket motor (SRM), both experiment and simulation of alumina molten flow patterns using the cold flow case. The combustion of aluminum composite propellants in SRM chambers causes high-temperature and pressure conditions resulting in the liquid alumina (Al2O3) as a combustion product, and it tends to agglomerate into molten droplets, which impinge on the propulsion chamber walls and then flow along the nozzle wall. This liquid alumina in the flow creates problems such as chemical erosion of the propellant and mechanical erosion of the nozzle. Thus, particle size and droplet distribution are considered to affect the erosive behavior. Furthermore, for the rocket motor, converging–diverging (C–D) of the nozzle is used because of its high performance in terms of the rate of change of momentum. In this study, to investigate the relationship between air velocity and molten particle size, the study was mainly focused on the horizontal arrangement of the combustion chamber with the cold flow with the liquid.