Influence of Different Duct Configurations on Flow Field Uniformity and Aerosol Distribution of Airborne Effluents in...

To ensure the accuracy of single-point sampling for airborne effluents in nuclear facilities, it is critical to clarify how stack and duct configurations regulate the flow field uniformity (velocity distribution) and aerosol distribution of the effluents. Taking the exhaust system of nuclear facilities as the research object, this study built a modular experimental platform covering seven duct configurations. Combined with experimental measurements and computational fluid dynamics (CFD) simulations, it systematically explored the impacts of duct configurations (including I, L, S, U types with smooth or right-angle transitions) and Reynolds numbers (Re = 5 × 104-1.5 × 105) on the coefficient of variation (COV) of velocity distribution and that of polydisperse aerosol distribution (average particle size: 5.2 μm). The CFD model established achieved excellent validation accuracy: over 93% of velocity data points showed a deviation between simulated and experimental values within ±15%, and the ratio of simulated to experimental aerosol concentration values followed a log-normal distribution with a mean (μ) of 1.13 and a standard deviation (σ) of 0.26. For flow field uniformity: long straight ducts lacked sufficient turbulence, resulting in a velocity COV >14% even at a length-to-hydraulic diameter ratio (L/D) of 20; elbows effectively reduced the velocity COV, with right angle transition elbows having a stronger turbulence effect than smooth-transition ones (e.g., L2 circular ducts reached a velocity COV <20% at L/D = 8, while L1 ducts required an L/D of 16 to achieve the same level); the S-type double-elbow ducts presented the highest flow field homogenization efficiency (S2 circular ducts achieved a velocity COV <20% at L/D = 7). For aerosol distribution: long straight ducts exhibited extremely poor aerosol mixing (COV >140% at L/D = 20); elbows promoted aerosol diffusion by enhancing vortex flow, with the right-angle transition S2 circular ducts performing the best (aerosol COV <20% at L/D = 4 and <10% at L/D = 20). When Re exceeded 104, further increasing the Re did not significantly improve flow velocity uniformity or aerosol mixing. The CFD method and regulatory requirements revealed in this study can provide technical support for optimizing sampling cross-sections in existing nuclear facilities and designing duct configurations for proposed ones.