Figure 4 shows the desorption isobar (1 bar) of our product obtained from
equilibrium laboratory experiments using Bassal’s method and described with
Oswin’s model (1992). A nonlinear optimisation method (Simplex) was used to
estimate the parameters of the model from the experimental results (Table 1). We
observe in Fig. 4 that the newly adjusted model is close to the experimental points
especially between 118 and 145”C, which is the temperature working range at the
output of the drum dryer. We can thus deduce the moisture content Xf from the
measurement of Tpe with a good precision.
In order to validate the use of the desorption isobar with the dried product
coming out of the drum, samples at different temperatures were taken just before
the knife and their moisture contents were determinated in the oven. Two different
emissivities were tested for the IR thermometer: &=0.85 and 0.95.
Figure 5 shows a good agreement between the experimental moisture content
obtained from drum drying experiments through classical oven methods and through
the isobar equation and temperature measurement for ~=0*85. We can also check
that the emissivity variation has little influence on the moisture content deduced
from the temperature.
Conclusion, the final product moisture content can be achieved by an infrared
thermometer T=TIR=f(Xj), giving through the isobar a local value of Xf, which is
precise (error 7% for T=118-148“(Z), without contact and quite cheap compared to
other methods of moisture measurement.