Numerical simulation of horizontal particle jets in a supercritical water environment based on an improved coarse-grained computational fluid dynamics–discrete element method

Horizontal particle jets are critical to supercritical water (SCW) reactors, as their flow behavior directly impacts reaction efficiency, heat transfer, and system stability. However, the rapid variation in fluid properties near the critical point and the complexity of particle–fluid interactions have hindered a comprehensive understanding of their kinetic characteristics. This study employs an advanced coarse-grained computational fluid dynamic–discrete element method to simulate horizontal particle jets in a SCW environment. By integrating the kinetic theory of granular flow with turbulence modeling, the proposed approach effectively captures rapid fluid property changes and complex particle–jet interactions. This study systematically analyzes the effects of transcritical and supercritical conditions on particle diffusion, fluid dynamics, and heat transfer, alongside sensitivity analyses of coarse-grained ratios on particle flow and thermal properties. The results demonstrate that higher fluid temperatures stabilize jet behavior, enhance mixing, and create more uniform temperature and density distributions. Particle diffusion is significantly influenced by temperature with increased fluid temperatures accelerating diffusion velocities. While translational velocity fluctuations decrease with rising temperatures, rotational perturbations and particle temperatures intensify before stabilizing. The coarse-grained method shows high accuracy in predicting particle behavior and heat transfer with deviations below 1%. These findings provide critical insight into the hydrodynamics of horizontal particle jets in SCW environments and offer valuable guidance for optimizing reactor design and improving operational efficiency.