THIN LAYER MODELLING OF OPEN SUN AND SOLAR DRYING KINETICS OF PULVERIZED MAIZE HUSKS

The open sun and solar drying of maize husks were investigated. Husks obtained from freshly harvested maize were cut into pieces, pulverized and 5 – 20 mm deep beds of husks were dried in open sun and solar dryer. The drying data were fitted to twelve thin layer drying models. The drying time increased with increasing depth of husks for both open sun and solar drying. The solar drying was faster than open sun drying, however, both took place in the falling rate period. The effective moisture diffusivities for open sun dying were 1.65 x 10-9 - 9.39 x 10-9 m2 s-1 while those for solar drying were 2.83 x 10-9 – 2.20 x 10-8 m2 s-1 for bed depths of 5 - 20 mm. The Wang and Singh model best fitted the sun drying data, whereas it only fitted the solar drying data for the 15 and 20 mm samples. The time required for drying pulverized maize husks, by radiation from the sun, can be essentially shortened by using thinner layer of husks and drying in a solar dryer rather than in open sun. The data provided by this study can aid the design of solar dryers for agriculture residues.