CFD-aided contraction-expansion static mixer design and operation

BALBI, MARÍA DEL PILAR; FLEITE S. N.; CASSANELLO MIRYAN

Congreso; WCCE11 ? 11th Word congress Chemical Engineering; 2023

Static mixers are devices that enable continuous mixing inside pipe-like systems without moving parts. They have been used for liquid-liquid mixing, gas-liquid dispersion, solid-liquid mixing and coagulation-flocculation, and as chemical reactor systems. In recent years, contraction-expansion devices have been found to be able to break suspended solids due to turbulence [1]. Hence, the aim of this work was to design and optimize a contraction-expansion static mixer (CE) to be used in solid-liquid and liquid-liquid mass transference limited reaction systems. The program Gerris Flow Solver [2] was sued to perform CFD simulations (Re = 10.000). The velocity vector norm RMS module (‖V ⃗ ‖_RMS) was calculated for different diameters (DC/DE) and longitude ratios (LC/LE), contraction to expansion (see figure below). The ‖V ⃗ ‖_RMS is known to correlate to turbulence and particles breaking in a given velocity vector field. Afterward, a CE device was built following RMSV optimal condition found by CFD, with a reservoir and a centrifugal pump. A TritonX100-water-sunflower oil mixture (1:1:1) was then used to test its capacity for dispersion and emulsification. A batch-stirred flask and a pipe were used as references. Turbidity versus time was measured (absorbance at 860nm) in samples to evaluate emulsion stability, comparing the initial separation velocities. Results showed a maximum RMSV at 0.57 DC/DE and 0.25 LC/LE. The emulsification assay showed a phase separation rate 2.7 times bigger for the stirred flask compared to the CE device, while the pipe setup showed an 11% higher separation rate than CE. A possible cause could be the generation of a smaller droplet-sized emulsion by the CE.