Quantifying Mixing using Magnetic Resonance Imaging

The overall goal of the following experiment is to use magnetic resonance imaging as a powerful tool to evaluate mixing and process equipment. This is achieved by combining two liquid streams in a split and recombined static mixer. Mr.Images are obtained by selecting an appropriate imaging protocol.

These images allow characterization of the mixer. Performance results are obtained for an application relevant to personal care products, but the procedure can be applied to a broad range of food, chemical, biomass, and biological fluids. The main advantage of using magnetic resonance imaging over other techniques, such as video, is that opaque materials can be visualized.

Additionally, the information is quantitative and component concentrations and the degree of mixing can be calculated. Visualizing, mixing. Using MRI can be helpful for validating computational fluid, dynamic simulations and manufacturing processes by detailed comparisons of spatially measured concentration distributions to calculated concentration distributions.

The SAR mixer is composed of a number of different plates laid into A PVC pipe. Each laser cut plate is composed of PMMA and cut 1.59 millimeters thick. Each plate has a rectangular key that aligns it along an acrylic rod.

In A PVC pipe, the plastic may be clear or opaque. The plates have various designs which have openings through which fluids can flow. The plates are laid into the pipe in a repeating pattern that results in tunnels that mix.

The two fluids that pass through the pipe plate S is used to stream the two fluids that enter the repeating motif. One fluid stream is at the center and the fluid streams above and below. They're at a relative flow rate of 10 to one.

Next, the fluids meet in an open channel, which is made by eight type C plates. The fluids are then physically separated into two vertical channels by eight plates of plate I.The next section is composed of 16 unique plates, which turn each fluid stream is twisted 90 degrees counterclockwise. The fluid then flows through eight plates that split the fluids into two horizontal channels.

The repeating motif finishes with eight open channel plates. Overall, the motif has repeated six times through the PVC pipe. Assemble a flow system to pump carbo pole solution through the inline split and recombined static mixer begin by positioning the mixer in the magnet.

The magnet is part of a single Tesla permanent magnet based imaging spectrometer with a peak gradient strength of 0.3 Tesla per meter and a nearly cubicle enclosure be able to control and record the mass flow rate of the test fluids. In addition, incorporate a pressure transducer upstream of the mixer to monitor pressure, a radio frequency coil made of a solenoid with four turns in cases of cylindrical volume and closely fits the PVC pipe. Lastly, two distinct solutions are connected to the intakes.

In this demonstration, the solutions will be carbopol with or without manganese chloride. Prepare the carbopol solution by slowly sifting a weighted amount of polymer into deionized water in a stirred tank. Neutralize the carbopol solution with a 50%sodium hydroxide solution to pH seven.

The neutralization allows the solution to achieve its maximum viscosity as the polymer swells in water. To form a gel, prepare a second doped carbo pole solution that contains the MR.Contrast agent manganese chloride. To characterize the flow behavior or rheology, use a standard coquette geometry at a fluid temperature of 25 degrees Celsius is to measure shear viscosity.

Use a steady state sheer stress sweep from 0.1 to 500 pascal in LA rhythmic mode with 10 points per decade and 5%tolerance. Then measure the strain over a frequency sweep from 628 to 0.63 rad per second in LA logarithmic mode with 10 points per decade. When selecting imaging parameters, we need to consider the total signal to noise in the image as well as the contrast and signal intensity between the doped region and the on region.

In this case, we've chosen a gradient echo sequence, and we've chosen concentrations of the. to give us a linear dependence of signal intensity on concentration. The MR sequence does not include flow compensation.

So to avoid motion artifacts, the imaging is performed on quiescent liquid imaging time is on the order of one to four minutes. Reposition the mixer to image the volumes at different axial locations. Slide the mixer tube axially through the magnet until the desired volume is at the center of the NMR coil in the center of the magnet.

Then repeat the imaging process. Finally, analyze the MR data with image analysis procedures to document the spatial distribution of component concentrations. In this work, the real logical properties of the two solutions were indistinguishable.

The solutions viscoelastic properties had the characteristic of a gel system with storage greater than loss, modulus and loss being fairly constant. The slope of a loss over storage increased at higher frequency, and the corresponding phase lag followed the same trend to evaluate the relative contribution of viscous forces to inertia forces during flow. Reynolds numbers were calculated as the average flow through the plates.

These values, which are much less than 1.0, indicate that viscous forces dominated the inertial forces. Thus mixing was by laminar stretching and shearing rather than turbulence. To illustrate the power of flow visualization using MRI, the following results are selected images at different axial locations.

The SAR mixer, effectively and uniformly splits flows as illustrated in the images of the H plates downstream from the first, second, and third mixing sections. The number of doped fluid stripes doubled through each mixing section. Changing the image value thresholds shows the stripes of doped fluid increasing with each pass through the motif.

A sequence of images through the 90 degree counterclockwise turn in the mixer shows how the vertical streams become horizontal streams in the mixing process through the whole tunnel. The two fluid streams are doubled many times When attempting to make these measurements, it's important to remember that the measurement time should be very short compared to the time for molecular diffusion to impact component concentration distributions. These experimental measurements of mixing are especially useful for testing the impact of constituent models of fluid rheology used in computational fluid dynamic simulations of mixing, and a split and recombined mixer.

After watching this video, you should have a good understanding of how to use magnetic resonance imaging to study concentration distributions in a static mixer.