Mixing In Static Mixer Research Articles

Numerical simulation of granular mixing in static mixers with different geometries

A static mixer is a fidelity engineered device for the continuous mixing of fluid/solid materials. To meet the requirements for mixing purpose, a proper design of the static mixer is important. In this study, we proposed various designs of static mixer based on the blade geometry. Six blade patterns including four twisted blades, four elliptical blades and other four combined geometries of two twisted blades and two elliptical blades are chosen to investigate its mixing performance. Mathematical model of the two-phase flow with fluid/solid interaction in the static mixer is presented. Numerical solution of the flow patterns of particulate solids, and the velocity and the pressure fields of the fluid in the static mixer with different blade geometries are carried out. To evaluate the quality of the mixing performance, the results obtained from six blade designs are compared via the relative standard deviation and the amount of pressure drop along the mixing path.

Effects of internal geometry modifications on the dispersive and distributive mixing in static mixers

In this article, different static mixer geometries are studied with an objective of achieving enhanced mixing performance. Design modifications such as incorporating perforations of varying size and different shapes of serrations are introduced to a standard Sulzer SMX geometry. CFD simulations are performed using COMSOL Multiphysics software to investigate mixing performance in these mixers under laminar flow conditions with an incompressible fluid as a working medium. For dispersive mixing, computational results were compared in terms of velocity field, pressure field, shear rate and extensional efficiency of each type of static mixer. Further, binary cluster particle tracer simulations in the flow domain are performed to compute the distributive mixing capacity of these static mixers which is quantified in terms of the standard deviation. Based on the computational results of both dispersive mixing and distributive mixing, the best modified static mixer geometry is proposed which facilitates significantly improved mixing compared to that of a standard SMX geometry.

Relationship between droplet size and fluid flow characteristics in miniemulsion polymerization of methyl methacrylate

AbstractStatic mixer (SM) can be applied for emulsification, but the fundamental understanding of the nature of fluid flow and mixing in static mixers, is however poor. Droplet size is a very important parameter in miniemulsion systems and affects strongly the mechanism of particle formation in polymerization reactions. In this study, static mixer was used as homogenization device for emulsification of methyl methacrylate (MMA). Re number (Re) was obtained for SM inserted tube in different flow rates. It was demonstrated the nature of fluid flow was turbulent under our experimental conditions. The relationship between droplet size—the most important variable in our study—and Weber number (We) was investigated. The results showed that the ratio of the droplet size to the pipe diameter was fit as an exponential function with an order of −0.35. The polymerization of created droplets under certain We values by SM showed that it is possible to obtain a reasonable 1 : 1 copy of droplets to the particles. All these, indicate that using relationship between We and droplet size allow one to obtain acceptable condition of droplet nucleation in miniemulsion polymerization. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Turbulent mixing and residence time distribution in novel multifunctional heat exchangers–reactors

Multifunctional heat exchanger–reactors show significant promise in increasing the energy efficiency of industrial chemical processes. The performance of these systems is conditioned by flow properties and is strongly geometry dependent. Here CFD simulation and laser Doppler anemometry (LDA) measurements are used to investigate the redistributing effects of the longitudinal vorticity generated by rows of inclined trapezoidal tabs on turbulent mixing in static mixers. Studies are carried out on three different configurations: in the first, the tabs are aligned and inclined in the direction of flow (the reference geometry for a high-efficiency vortex (HEV) static mixer), in the second, a periodic 45° tangential rotation is applied to the tab arrays with respect to one another, and in the third the reference geometry is used in the direction opposite to the flow direction (reversed direction). The mixing efficiency, taken as the resultant of the momentum-transfer efficiency of the “mean” flow at different scales, is studied. Macro-mixing entails the dispersive capacity of the flow at the heat exchanger–reactor scale, and is generally measured by the residence time distribution (RTD). At the intermediate scale, meso-mixing is governed by the turbulent fluctuations; this process of turbulent mixing can be characterized by the turbulence kinetic energy (TKE). Micro-mixing is characterized by the local rate of turbulence energy dissipation and is related to the progress of fast chemical reactions and selectivity. It is shown here that the reversed-array arrangement (the third configuration) provides the best performance in micro- (50%) and meso-mixing (25%), but exhibits an approximately 40% increase in power consumption over the classical HEV (reference) geometry and somewhat pronounced bimodal behavior in the RTD.

Experimental characterization and multi-scale modeling of mixing in static mixers. Part 2. Effect of viscosity and scale-up

Static micro-mixers are used in precipitation processes to avoid mixing limitations. The mixing performance of these mixers, which are used in this study to mix two streams of different viscosity, is characterized using competitive-parallel chemical reactions and computational fluid dynamics (CFD). This work is an extension of a previous paper where mixing of fluids with equal viscosity has been studied [Lindenberg, C., Schöll, J., Vicum, L., Brozio, J., Mazzotti, M., 2008. Experimental characterization and multi-scale modeling of mixing in static mixers. Chemical Engineering Science 63, 4135–4149]. It is found that the mixing performance in terms of reaction yield and mixing time decreases slightly with increasing viscosity ratio in a two jet vortex mixer (Roughton mixer). In the Y-mixer the trend is the same at low flow rates, but it is the opposite at large flow rates due to a symmetry breaking phenomenon. The Roughton mixer is scaled-up using the CFD model and a linear relationship between scale-up factor and mixing time is observed. Finally, it is shown that mixing times can be described satisfactorily as a function of velocity, jet diameter and viscosity.

Markov-chain modelling and experimental investigation of powder-mixing kinetics in static revolving mixers

This study aims to develop a general model that is able to describe powder flow and mixing in static mixers, regardless of the type of mixer or the mixing configurations. The process model is based on a homogeneous Markov chain describing the flow of each component through the mixing zone by a series of interconnected cells. It accounts for the number of mixing elements and their disposition in the mixer, as well as particle segregation via different transition probabilities. Some simulations are given to emphasize this particular aspect. Other outcomes of the model include the number of passages to reach a required mixture quality, as well as the asymptotic distribution of components. A laboratory static mixer of revolving type was designed specially for this study. It comprises up to 10 mixing sections, and its high internal voidage favours free flow of the powder. Segregating and non-segregating mixtures have been used to test the model and adjust unknown parameters. The model gives very satisfying results. In particular, it is able to account for the oscillating character of mixing kinetics due to particle segregation. It is also suggested that these parameters could be linked separately to powder flowability and mixing element characterization.

Experimental characterization and multi-scale modeling of mixing in static mixers

Mixing in static mixers is studied using a set of competitive-parallel chemical reactions and computational fluid dynamics (CFD) in a wide range of operating conditions. Two kinds of mixers, a wide angle Y-mixer and a two jet vortex mixer, referred to as Roughton mixer, are compared in terms of reaction yields and mixing times. It is found that the Roughton mixer achieves a better mixing performance compared to the Y-mixer. The effect of flow rate ratio on mixing in the Roughton mixer has been studied as well and it is shown that the mixing efficiency is not affected by the flow rate ratio. Moreover, experimental results and model predictions are in good agreement for all mixer geometries and operating conditions. CFD is used to calculate absolute mixing times based on the residence time in the segregated zone and it is shown that mixing times of less than 1 ms can be achieved in the Roughton mixer. In addition, CFD provides insight in local concentrations and reaction rates and serves as a valuable tool to improve or to scale-up mixers.

Micromixing and fast chemical reactions in static mixers

Turbulent reactive mixing in static mixers has not been widely studied. Knowledge of the turbulent energy dissipation rate is needed to make predictions about the course of chemical reactions in mixing elements. It was determined by applying the engulfment model of micromixing to the measured product distributions of fast competitive-consecutive diazo couplings between 1-naphthol and diazotized sulphanilic acid. Three static mixers, differing mainly in the width of their channels (hydraulic diameters from 0.0021 to 0.0053 m), were studied. Dissipation rates in the range 700–1000 W kg −1 were obtained when the superficial liquid velocity was 2 m s −1 and the viscosity was 7.9 mPa s. The channel width influenced these values as well as the turbulent part (29%−67%) of the total energy dissipation. The performance of the static mixers was compared with that of the empty tube. Turbulence decay downstream from a mixer, the spacing between the feed pipe and the first element and the change from semi-batch to in-line operation were also investigated.