TITLE:
Mass Transfer in Infrared Drying of Gel-Coated Seeds
AUTHORS:
Antônio M. Barbosa Neto, Luanda G. Marques, Manoel M. Prado, Dermeval J. M. Sartori
KEYWORDS:
Gel Coating; Shrinking Particles; Infrared Drying; Mass Transfer
JOURNAL NAME:
Advances in Chemical Engineering and Science,
Vol.4 No.1,
January
24,
2014
ABSTRACT: In order to contribute for a better understanding of
mass transfer in drying of shrinking particles, in this study shrinkage and
drying characteristics of sorghum seeds encapsulated into gel-based polymeric
matrix were experimentally determined by using infrared (IR) radiation. IR
drying of gel coated seeds was carried out at three different temperatures (65℃,
80℃ and 93℃). The shrinkage of the individual particles during drying was quantified
by means of the volume and surface area changes evaluated from geometric
measurements. The product quality was evaluated in terms of the changes of
particle density and percent of cracks in gel coating incurred during drying.
Surface area and volume of the gel-seed system decreased about 65% and 80% until the end of the process,
respectively, stressing the need to take into account
the surface area changes to calculate water flux density as function of
moisture content and obtain an accurate interpretation of the drying mechanisms
well as to include the volume shrinkage in mass transfer models to determine
reliable values of moisture diffusivity. The IR drying behavior of gel-coated
seeds was then characterized by the presence of three drying periods: heating
up, constant moisture flux and falling moisture flux. Accelerated drying of gel
coated seeds was obtained by applying higher IR radiation intensities. The
effect of IR source temperature on the particle shrinkage was more pronounced
at the constant moisture flux period and practically negligible at the
decreasing moisture flux period. Neglecting shrinkage of individual
coated-seeds during IR drying led to an erroneous absence of constant flux
period and overestimation of the mass transfer by diffusion. Apparent density
of the particles was greater at low-temperature IR drying than at high-temperature
IR drying. Coated particles keep their original geometry, but a significant
cracking of gel coating was observed at rapid drying rate conditions.