Simple and Low-Cost Exposed -Layer Grain Drying Apparatus

  • Tilahun Seyoum Workenh Alemaya University, College of Agriculture, Department of Agricultural Engineering, P.O.Box 138, Dire Dawa, Ethiopia
  • Patrick M Grace University College Dublin, Faculty of Engineering and Architecture, Department of Agricultural and Food Engineering, Earlsfort Terrace, Dublin 2, Ireland.


Thin-layer drying apparatus was developed from standard “off-the- shelf” equipment: a fan convection laboratory oven and a weighing scale. Using this apparatus the thin-layer drying data for wheat under constant conditions were obtained for a range of drying air temperature from 30°C to 150°C and the initial moisture content from 0.20 to 0.42 (d.b.). The smooth drying characteristic curves were obtained and used to develop coefficients for three thin layer models namely: Grace (modified Henderson) model, Chen and Johnson, and the numerical diffusion models. The Grace and the Chen and Johnson models were the best at describing the drying curves giving a standard error of the moisture ratio less than 0.027. The drying apparatus enables monitoring of the sample weight during drying without opening the oven. The drying air properties (relative humidity and temperature) inside the oven were kept constant throughout drying. The next special feature of it was that the sample kept on drying even at the time of recording its weight. No temperature change was observed after the oven was switched on after 30 seconds. This apparatus is relatively simple and can be used for drying of biological materials. However, several thin-layer grain drying researchers have obtained moisture loss by using fast sampling devices through out the drying period. During the study a fast sampling device was not used because it was necessary to turn off the oven before taking measurements.

Key words: Drying apparatus, thin-layer grain drying, drying model

J Food Tech in Africa (2002) 7, 45-51

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eISSN: 1028-6098