Temperature mapping of particles during aseptic processing via magnetic resonance imaging
Kantt, Carlos Alberto
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Permalink
https://hdl.handle.net/2142/23345
Description
Title
Temperature mapping of particles during aseptic processing via magnetic resonance imaging
Author(s)
Kantt, Carlos Alberto
Issue Date
1996
Doctoral Committee Chair(s)
Litchfield, J. Bruce
Department of Study
Agricultural and Biological Engineering
Discipline
Agricultural and Biological Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Agricultural
Language
eng
Abstract
Different Magnetic Resonance Imaging (MRI) techniques for temperature measurement of particles undergoing aseptic processing were studied. A variable flip angle gradient echo sequence was initially tested. With this sequence T1 maps were obtained from two images acquired in sequence with a total imaging time of approximately 25 seconds. With a T1 vs temperature calibration, temperature determinations were possible. Reasonable results were obtained with phantoms at room temperature, but temperature maps of potato cylinders being heated by water did not follow the expected trend of heat penetration from the outside to towards the inside of the potato.
Temperature measurement through T1 weighted spin-echo imaging showed non temperature dependent contrast, due to inherent differences in T1 in different sectors of the white potatoes that were being studied. T1 spin-echo maps of red potato cubes being heated by flowing water at approximately 100$\sp\circ$C showed no temperature dependent profile.
The use of the change in precession frequency of the water proton with temperature (known as chemical shift imaging or phase mapping) proved more successful. Temperature maps of a gel, and of cooked and raw red potatoes were obtained during heating from 20 to 60$\sp\circ$C. Temperature resolution ranged between 0.3 and 3$\sp\circ$C, decreasing with increasing temperature due to a reduction in the signal to noise ratio. The difference in temperatures determined by MRI and thermocouples was less than 5$\sp\circ$C.
Chemical shift imaging was also used to obtain two dimensional temperature maps in potato particles undergoing aseptic processing. Large particles $(3/4\times3/4\times3/4\sp{\prime\prime})$ showed a temperature difference ($\Delta$T) of up to 22$\sp\circ$C in images obtained 45 seconds after exiting the heat exchanger with the $\Delta$T of the carrier fluid across the heat exchanger being approximately 30 to 45$\sp\circ$C. No $\Delta$T was measured in particles smaller than $1/2\times1/2\times1/2\sp{\prime\prime}$ pumped at less than 6 gal/min. Using a finite element model of the heating process, average fluid to particle convective heat transfer coefficients $\rm(h\sb{fp})$ in the range of 600 to 2500 W/m$\sp2\sp\circ$C were estimated for the large particles. For the smaller particles only a lower limit for $\rm h\sb{fp}$ of approximately 3000 W/m$\sp2\sp\circ$C could be determined.
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