Paper Submission
09. Heat and Mass Transfer
MIXING OF VISCOELASTIC FLUIDS IN STATIC MIXERS
Numerical study of the mixing of viscoelastic fluids in SMX static mixers was performed for understanding the relative importance of shear thinning and elastic effects on mixing, and the geometric parameters of the mixer for optimization, with the aid of COMSOL software. The velocity and pressure were calculated using two constitutive models, the Carreau model and the Giesekus model, and the mixing was accessed through the simulation of mass transport of dilute species. The shear thinning effect is well described by the Carreau model, while the Giesekus model could further accounting more adequately the elastic effect, such as the prediction of the first and second normal stress differences. First, the calculation was validated using the experimental results in literatures. The calculations using Giesekus model agree with the mixing experiment within experimental error, while the Carreau model underestimates the mixing by about 7% at the exit of a 9-element mixer, indicating that the elastic effect could contribute additional mixing. Both models could be applied for mixer design as they predict qualitatively the same tendency for mixer performance, but much more computation time (about 7.5 times longer) is required for the Giesekus model. Secondly, parametric study of the geometric parameters of the SMX mixer was performed using the Carreau model with various fluids. It was found that the performance of standard SMX mixer designs is not optimized in general, while the design rule proposed in the literature through optimization via the so-called “Mapping Method” for Newtonian fluids, Np = (2/3)Nx – 1 for Nx = 3, 6, 9, 12, … , could provide better performance also for viscoelastic fluids. Here Nx is the number of crossing bars over the width, and Np is the number of parallel bars over the length of the mixer element. However, more than one set of parameters for better mixing could be found, and the one with fewer cross-bars should be chosen for smaller pressure drop across the mixer.
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Author Information
Y. L. Liao
Mr.
H. H. Lai
Mr.
Y. H. Bai
Mr.
K. T. Lai
Mr.
C. F. Chen
Mr.