Enhancement of the performance of a static mixer by combining the converging/diverging tube shapes and the baffling techniques

The performance of a newly designed static mixer is explored in this paper by numerical simulations. It concerns a converging/diverging circular tube equipped with opposing and staggered baffles. This new design of static mixer presents a cost-effective, easy-to-design, easy-to-maintain choice, with a minimum pressure drop and a good mixing index at low Reynolds numbers (from 60 to 700), to the currently used static mixers. The investigation was carried out numerically for different baffle clearances (cl/D = 0.3, 0.5, 0.7 and 1.0, respectively) and inclination angles (alpha = 0 degrees, 30 degrees and 45 degrees, respectively), different ratios of inlet diameter-to-outlet diameter (D-d = d/D = 0.6, 0.8, 1.0, 1.2 and 1.4, respectively) and different Reynolds number values. The obtained results revealed that the diverging tube favors the mixing index while reducing the pressure drop. For a dimensionless baffle clearance (cl/D) of 0.5 and Re = 700, the mixing index has been increased from 0.78 for a simple tube (d/D = 1) having vertical baffles (alpha = 0 degrees) until 0.95 for a diverging tube at the ratio (d/D) of 1.4 with the same vertical baffles (alpha= 0 degrees). The increase in the ratio d/D has also yielded a decrease in pressure losses. Compared to the simple static mixer without baffles and having the same inlet as outlet sections, the maximum enhancement in mixing index was about 315.84% when d/D = 1.4 and Cl/D= 0.3 and alpha= 0 degrees. However, a reduction in pressure drop by about 92% may be obtained when alpha= 30 degrees with only a reduction in mixing index by 14% (compared to alpha = 0 degrees).