In-line characterization of fluid mixing
- University of California, Food Science and Technology, Davis, United States
Static mixers are implemented across many process industries and are especially effective in mixing, heating and reacting processes. SMX mixers, which split, rotate and recombine flow, are considered the best static mixer for laminar mixing for a wide range of fluid viscosities. The objective of this work was to characterize mixing within a 9-element SMX mixer for miscible liquids using magnetic resonance imaging (MRI).
The SMX mixer was comprised of 9 DN25 (1") SMX elements fabricated in ABS-like (acrylonitrile-butadiene-styrene) material. Each element had a diameter of 25.4 mm and a length of 25.4 mm and was made of six planes of 3.18 mm x 1.9 mm bars spaced 3.18 mm apart. Three planes of bars were spaced 9 mm apart with the remaining three planes placed orthogonally. The axial position was offset 45° from both sets of planes. The SMX mixer assembly was placed in the imaging section of a 1 Tesla permanent magnet based imaging spectrometer (Aspect Imaging, Shoham, Israel) with a 0.3 T/m peak gradient strength. Both Newtonian (glycerine) and nonNewtonian (carboxymethyl cellulose) fluids were evaluated through the acquisition of multi-slice GRE MR images that provided spatially resolved concentrations of 2 equal volume fluids.
The MR images were viewed qualitatively and quantitatively. Mixing indices as a function of axial positions indicated that mixing is more rapid for Newtonian fluids than the nonNewtonian fluid for 50-50 by volume mixing. The experimental trials showed similar mixing patterns and more rapid mixing than given by the curve established by computational methods1. Characterization of mixing behavior within the SMX mixer allows improved prediction of performance based on fluid properties, flow ratio and injection location.
