Effects of direct sun drying of maize grains on perforated and unperforated surfaces

Abstract

Sun drying of maize grains on unperforated and perforated surfaces was conducted under simulated solar radiation intensity of of about 800 W/m and in the field, where solar radiation intensity was variable. The drying depths employed were 10, 20, 30 and 40 mm under simulated solar radiation conditions and 20 and 40 mm in the field. The response variables measured were weight loss at all depths and moisture content and temperature distributions in the 40-mm depth bed. The results in terms of overall drying rates indicate that, at depths greater than 10 mm, the perforated surface was superior (P < 0.05) to the unperforated and at 40 mm the effect was about double that of the control. Changing of drying depth from 10 to either 20 or 30 mm on the perforated surface did not affect the specific drying rates significantly (P < 0.05) except on 4mm depth. On the unperforated surface the overall specific drying rates decreased significantly (P < 0. 05) with change of drying depth from 10 to 20 mm and above. Lower moisture gradients were achieved on the perforated surface and despite the higher drying rates temperatures in the bed were lower than on the uperforated surface. In order for high drying throughput to be achieved, drying depth of about 30mm on perforated surfaces is recommended. Sun drying in the field yielded results that were similar to those obtained under simulated solar radiation conditions despite the fluctuating nature of terrestrial solar radiation intensity. Further work in the field, focusing on the effect of aperture size of perforations and the gap size between the drying surface and the ground floor for perforated surfaces is needed.

Keywords: Sun drying, simulated solar, radiation, unperforated surface, perforated surface

Tanzania J. Agrlc. Sc. (2000) Vol. 3 No. 2, 97-102