MODELLING OF MOISTURE PROFILES IN PADDY RICE DURING DRYING MAPPED WITH MAGNETIC RESONANCE IMAGING (MRI)

摘要

During the drying process, internal water migration is often the limiting factor for thernoverall water transfer. In order to simulate a drying process, an accurate determinationrnof the water diffusivity (D) in the material is always necessary. For biological productsrnD is known to be low and to vary with moisture content (X) and temperature (T).rnD=f(X, T) can be estimated from the fitting of moisture profiles determined by nonintrusivernNMR imaging. This work first presents the experimental results obtained onrnpaddy rice. The moisture profiles were measured during the drying process using arnBruker AMX400 spectrometer, equipped with a micro-imaging device at the H+rnfrequency of 400 MHz. Four drying experiments at two different air temperatures werernperformed. A Constant Time Imaging (CTI) technique proved to be useful to obtain thernmoisture content map in a central slice section of the kernel with 3 mm thickness,rnallowing a spatial resolution of 0.1 mm. This method provided access to low moisturerncontent and low water mobility data. Then a diffusive model was developed using arncylindrical geometry, taking into consideration the shrinkage during drying.rnUnidimensional water profiles from axes of the elliptic section of the kernel werernselected in order to determine the diffusivity parameters of the drying model.