Article,
Modeling of moisture profiles in paddy rice during drying mapped with magnetic resonance imaging
Chemical Engineering Journal, 86 (1-2): 173--178 (2002)
Abstract
During the drying process, internal water migration is often the limiting
factor for the overall water transfer. In order to simulate a drying
process, an accurate determination of the water diffusivity (D) in
the material is always necessary. For biological products D is known
to be low and vary with moisture content (X) and temperature (T).
D=f(X,T) can be estimated from the fitting of moisture profiles determined
by non-intrusive NMR imaging. This work first presents the experimental
results obtained on paddy rice. The moisture profiles were measured
during the drying process using a Bruker AMX400 spectrometer, equipped
with a micro-imaging device at the H+ frequency of 400MHz. Four drying
experiments at two different air temperatures were performed. A constant
time imaging (CTI) technique proved to be useful to obtain the moisture
content map in a central slice section of the kernel with 3mm thickness,
allowing a spatial resolution of 0.1mm. This method provided access
to low moisture content and low water mobility data. Then a diffusive
model was developed using a cylindrical geometry, taking into consideration
the shrinkage during drying. Uni-dimensional water profiles from
axes of the elliptic section of the kernel were selected in order
to determine the diffusivity parameters of the drying model. � 2002
Elsevier Science B.V. All rights reserved.
