Temperature Mapping of Particles During Aseptic Processing with Magnetic Resonance Imaging

Magnetic Resonance Imaging (MRI) was used to obtain 2-dimensional temperature maps in potatoes undergoing aseptic processing. The change in precession frequency of protons served as the temperature indicator. The larger particles (6.9 and 3.84 cm3) showed a δT (T_surface - T_center) of up to 22±0.4°C 45s after exiting the heat exchanger with the δ (T_outlet - T_inlet) of the carrier fluid in the heat exchanger at 30 to 45°C. No AT was measured between the center and the surface of particles <2.05 cm³ pumped at <22.7 L/min. The average fluid to particle convective heat transfer coefficient (h_fp) for the heat exchanger and holding tube was calculated using a finite element method. The hfp was from 600 to 2500 and >3000 W/m²°C for the large (6.9 cm³ cubes) and smaller particles respectively.