Flow analysis and thermochemical insight during supercritical water gasification of polypropylene particles

This study presents a comprehensive numerical investigation of polypropylene particle gasification in supercritical water using particle-resolved direct numerical simulations in both two-dimensional (2D) and three-dimensional (3D) configurations involving a single particle or three particles in interaction. The results are analyzed systematically to assess the effects of dimensionality, particle position, and particle Reynolds number (Rep = 50–125) on flow dynamics, interfacial heat and mass transfer, and species distribution. 3D simulations reveal higher drag coefficients, Nusselt numbers, and Sherwood numbers than 2D simulations, primarily due to thinner boundary layers and weaker Stefan flow. While 2D simulations capture general trends, 3D modeling is essential to resolve boundary layer development and wake interactions accurately. In multi-particle arrangements, downstream particles experience significant shielding in 2D, whereas 3D wake structures mitigate these effects. Species H2 shows complex, nonlinear behavior due to high diffusivity and strong coupling with local flow, unlike the approximately linear temperature trends of CO2, CO, and CH4. Higher particle Reynolds numbers enhance convective transport but reduce residence time, heat release, and surface reactions, slowing particle shrinking rates. These findings provide key insight into supercritical water gasification and support the development of predictive models and scalable reactor designs for plastic waste conversion.