S. Cenkowski et al., DYNAMICS OF DRYING BENTONITE IN SUPERHEATED STEAM AND AIR AS A MODEL FOOD SYSTEM, Canadian agricultural engineering, 38(4), 1996, pp. 305-310
The objective of this research was to compare temperature patterns, dr
ying rates, and diffusivities of bentonite as a food model with a high
concentration of solids dried in hot air and superheated steam at 160
degrees C. In our preliminary investigations on the drying of liquid
food droplets in hot air and superheated steam, spherical samples of 1
3.5 mm in diameter were prepared from chemically stable bentonite past
e. In superheated steam drying, bentonite samples reached the saturati
on temperature for steam (100 degrees C) after the first minute of dry
ing. During this period the samples gained approximately 0.1 kg/kg dry
basis (db) of moisture, due to condensation of water on the surface o
f the sample. In air drying at 160 degrees C, the temperature of a sim
ilar sized sample gradually increased to a wet bulb temperature of 80
degrees C over a 10 min period. The drying rate in the superheated ste
am was higher by 8 to 10% than in the 160 degrees C air in the initial
stage of drying. However, this situation reversed when samples reache
d the falling rate-of-drying stage. For this period and below moisture
content of 0.10 kg/kg db, the overall diffusion coefficient was 50 to
80% higher for samples dried in the 160 degrees C air than in superhe
ated steam of the same temperature.