Flow regimes and drop break-up in SMX and packed bed static mixers

• Published in: Chemical engineering science 2012-05, Vol.73, p.354-365
• Main Authors: Baumann, A., Jeelani, S.A.K., Holenstein, B., Stössel, P., Windhab, E.J.
• Format: Article
• Language: English
• Subjects: Applied sciences; Chemical engineering; Dispersion; Drop break-up; emulsions; Exact sciences and technology; Hydrodynamics of contact apparatus; mixers; Packed bed; prediction; specific energy; Specific energy dissipation; Static mixer; steady flow; Turbulent flow
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2012.02.006

We present experimental investigations with SMX and packed bed (PBM) static mixers for power consumption during steady flow of Newtonian fluids and liquid–liquid dispersion in turbulent flow. Newton (Ne) and Reynolds (Re) numbers for obtaining power characteristics were calculated based on interstitial flow in the static mixers. The proposed correlations agreed well with those in literature and showed that at very high Re, meaning in fully turbulent flow, Ne for PBM is almost half of that for SMX. Furthermore, PBM and SMX were compared by measuring drop size distributions and pressure drops during formation of oil-in-water emulsions with different flow rates and residence times, the latter being varied by passing emulsions several times through static mixers of different lengths. The prediction of median drop diameter in terms of Weber (We) and Newton numbers using Kolmogorov–Hinze theory for isotropic turbulent-inertial flow regime involving specific energy dissipation rate is found to be valid only for SMX static mixer. In contrast, the turbulent flow is anisotropic in PBM resulting in higher exponents of We and Ne than theoretically predicted. In addition, the use of short static mixers enabled to present models including an empirical term to account for kinetic effects. However, the median diameters of drops formed in SMX and PBM are about the same at a given specific energy dissipation rate, even though the corresponding volume flow rate is higher in SMX than that in PBM. [Display omitted] ► Comparison of SMX and packed bed static mixers regarding power consumption. ► Calculation of dimensionless numbers based on interstitial flow. ► At high Reynolds number, lower Newton number in packed bed mixers than in SMX. ► Comparable median drop diameters for emulsions formed in SMX and packed bed mixers. ► Reasonable drop size prediction in short mixers by considering kinetic effects.