Studies of rheological and mixing properties of multi-component systems using magnetic resonance imaging.

摘要

Mixing behavior and rheological characterization studies were conducted using Magnetic Resonance Imaging (MRI).; The mixing was characterized with model systems, carbon black powder systems, and starch systems. The series of mixing images for each system were analyzed statistically using first and second order statistics. MRI techniques show great potential for use in mixing studies of various systems. The model systems revealed that the viscosity of a fluid has more impact on the extent of mixing than the effect of particle loading has. The surfactant concentration and impeller speed were important factors for the carbon black mixing. The release of trapped air was affected by the impeller speed and surfactants. The characterization of starch gelatinization was not successful using MR images.; Rheological characterization of tomato concentrates was performed using MR flow imaging to obtain the effects of temperature and concentration. The flow profiles were best characterized by a Herschel-Bulkley expression. Apparent viscosity showed Arrhenius-type behavior with temperature. Yield stresses and slip velocities were determined directly from the flow profiles and functions of temperature and concentration. Based on this study, the RTD of tomato concentrates is narrower with increasing temperature and concentration. The chemical gelatinization of starch was characterized by the spin-spin relaxation time (T₂) measurements of three types of corn starches; unmodified, acid-thin, and oxidized corn starches. The T₂ varied with time, significantly increasing up to 8 hours of gelatinization. The corn starches displayed similar T ₂ behavior with different magnitudes for each corn starch. Spin-spin relaxation times were sensitive to the changes during chemical gelatinization of corn starches.