Hydrodynamic mechanisms of jet mixing-induced cooling enhancement​ for reactor thermal stability using an experimental-CFD approach

Abstract

Thermal runaway is a severe process safety hazard, particularly in stirrerless reactors, where the absence of mechanical agitation limits heat redistribution under abnormal operating conditions. Jet mixing cooling combines coolant injection with internal circulation; however, the hydrodynamic mechanisms by which jet configuration influences the transient thermal response remain insufficiently characterized. This study integrates experiments and Computational Fluid Dynamics (CFD) to examine jet Reynolds number (Rej) effects for a 45° side jet and 90° axial bottom jet in a cylindrical vessel (0.16 m in diameter and 0.24 m in liquid height). Experiments were conducted at Rej = 3828, 4290, 4752, and 5148. After validation, the CFD analysis was extended to Rej = 5610 and 5808. The CFD model was validated for the representative 90° axial bottom jet at two thermocouple locations, with average relative errors of 0.91% at TC1 and 0.88% at TC2. Increasing Rej reduced t50 and t90 by approximately 35% to 36% for both configurations. At the same Rej, the axial bottom jet reduced t50 by 7.2% to 8.1% and t90 by 3.8% to 5.5% relative to the side jet, consistently providing better cooling performance. The CFD fields show that increasing Rej increases transport intensity, whereas jet orientation determines how momentum is organized within the vessel. The axial jet develops symmetric recirculation throughout the vessel depth, whereas the side jet produces an asymmetric circulation pathway. The results establish how jet momentum and hydrodynamic structure influence transient cooling and provide practical guidance for stirrerless reactor cooling systems during thermal excursions.