CFD simulation of methanol and soybean oil mixing in SMX static mixers: the effect of length-to-diameter ratio

Efficient mixing of oil and alcohol is critical for high-quality biodiesel production through transesterification. Static mixers like the Sulzer SMX type, offer energy-efficient mixing but require optimization for practical applications. This study employs computational fluid dynamics (CFD) to investigate the hydrodynamic behavior and design optimization of SMX static mixers for methanol and soybean oil mixing. Three length-to-diameter (L/D) ratios (6, 10 and 14) and inlet velocities (0.283, 0.566, and 1.132 mm/s) were simulated under laminar flow conditions. The results indicated that increasing the L/D ratio enhances mixing efficiency but significantly increases the pressure drop. Although the highest mixing efficiency is obtained at L/D = 14, the incremental efficiency gain becomes progressively smaller relative to the rising hydraulic losses. As a result, an L/D ratio of 6 is identified as the optimal configuration, providing a favorable balance between mixing performance and energy consumption under viscous-dominated laminar flow conditions. The pressure drop exhibits an approximately linear dependence on inlet velocity, which is consistent with laminar flow behavior.