DESIGN OF A CONTINUOUS FLOW MAGNETIC RESONANCE SYSTEM FOR RHEOLOGICAL CHARACTERIZATION

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2022-12
Bölükkaya, Zikrullah
In food processing, handling, pumping, and extrusion of dilute and viscous fluids, emulsions, and suspensions are important for production purposes. Magnetic Resonance Imaging (MRI) offers the possibility to measure the rheological properties of different fluids in a non-invasive mode and is highly selective (in situ, online) to study the structural changes, or inner transport processes (without wasting samples and disturbing production) in flowing materials. In this study, a bench top Magnetic Resonance Imaging system operating at a frequency of 24.15 MHz (~0.50 T), equipped with a radio frequency coil of 10mm was converted to a flow-MR system or the so-called MR-Viscometer to measure the rheological constants of different Newtonian and Non-Newtonian fluids. At the first step, mechanical energy calculations were made to determine the system dimensions, and fittings and to integrate the pressure transducer of the system. Since a peristaltic pump was used there was the ‘pulsation’ problem, which could have caused problems in the MR velocity images was observed. Thus, a dampener was added to the system by making the proper calculations. Once the design calculations were complete and the system was set up, experimental trials were carried out to test the system. Almond milk and whole milk were tested at different pump flow rates to check whether the system was operating properly. Almond milk was a shear-thinning fluid (K=0.0254 Pa.s, n =0.783) whereas whole milk was Newtonian (=0.0032 Pa.s). The error between theoretical and experimental pressure differences was found to be 31-40% for whole milk and 23-45% for almond milk. It was interesting to observe that at different flow rates there was a significant and positive correlation (r=0.99, p<0.05) between the experimental and theoretical pressure differences which indicated that there was an ‘inherent’ error associated with the pressure measurements. Error rates of whole milk higher at low flow rates were explained by the high slip velocities and the high error at high flow rates for almond milk was explained with dampener problems. Measurements were also conducted with methylcellulose solutions and rheological constants were compared with the conventional rheometer experiments. ‘n’ values were not found to be different for the flow MR and conventional measurements (p>0.05) whereas K values were significantly higher in flow MR results. However, despite the K values higher in flow MR results, there was a positive and significant correlation (p<0.05) between the two measurements confirming that the system was working properly but the pressure measurement error needs to be corrected to get an equal number from both methods.

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Citation Formats
Z. Bölükkaya, “DESIGN OF A CONTINUOUS FLOW MAGNETIC RESONANCE SYSTEM FOR RHEOLOGICAL CHARACTERIZATION,” M.S. - Master of Science, Middle East Technical University, 2022.