233 Diffusion model for thin layer drying process of corn O Hacıhafızo˘ glu 1∗ , A Cihan 1 , K Kahveci 1 , and C Korkmaz 2 1 Department of Mechanical Engineering, Trakya University, Edirne, Turkey 2 Hayrabolu Vocational School, Namık Kemal University, Tekirda˘ g, Turkey The manuscript was received on 21 November 2008 and was accepted after revision for publication on 13 May 2009. DOI: 10.1243/09544089JPME253 Abstract: In this study, single-layer drying behaviour of corn is simulated by liquid diffusion model by using the experimental data for drying temperatures between 40 and 70 ◦ C and for a drying rate of 2m/s. Three different geometries representing a corn grain, slab, sphere, and cylinder are taken into consideration to specify the geometry which yields best results. The drying curves are obtained by minimizing the sum of squared differences between experimental data and theoretical predictions. Results show that drying behaviour of corn can be modelled reasonably by liquid diffusion model and that the solution based on sphere geometry is in better agreement with the experimental drying behaviour as compared with other geometries. The results also show that the temperature and the movement velocity of moisture from the inner part of corn grains towards the outer part have a quite significant effect on the drying rate. Keywords: corn drying process, thin layer, liquid diffusion, moisture ratio, concentration 1 INTRODUCTION Corn is one of the main agricultural products through- out the world and an important industrial raw material in starch industry because of its rich starch content and useful byproducts obtained during starch extrac- tion [1]. Corn grains are not only used in making bread and for human nourishment as an appetizer, but are also utilized in glucose and livestock fodder industries. The germs too are used for the extraction of cooking oil. Corn has high moisture content at harvest and if it is not subjected to an appropriate drying process, it decays due to infestation and mold growth. Drying process is generally performed by heating the ambient air and then sending it by forced convection over the crops to be dried. The aim in heating the air to a certain temperature is to reduce the relative humidity of the air, which has a positive effect on the drying potential. The drying rate of corn is affected by a number of factors such as initial moisture content, drying air tem- perature, relative humidity, and airflow rate. The type of grain and its variety, drying method, dryer type, and efficiency are other important factors that influence the drying rate. There are several studies available in ∗ Corresponding author: Department of Mechanical Engineering, Trakya University, Ahmet Karadeniz Yerleskesi, Edirne, Turkey. email: oktayh@trakya.edu.tr the literature investigating the aforementioned factors on the drying rate of corn. Soponronnarit et al.[2, 3] have studied the drying behaviour of corn in a batch fluidized bed dryer at various drying temperatures. Their results indicate that moisture transfer is con- trolled by internal diffusion. In an experimental study, Krokida et al.[4] have found that drying air velocity has almost no effect on the drying rate of corn and the actual effect is caused by changing the drying air temperature. Drying behaviour of hydrated and fresh corn grains has been examined [5] and it has been found that fresh corn grains have lower diffusion coef- ficients and the difference between the two diffusion coefficients increases with increasing drying tempera- ture. Corn drying in a fluidized bed dryer with an inert energy carrier has been investigated [6]. Their results show that the presence of inert particles enhances the rate of drying, considerably. After an experimental study, Prachayawarakorn et al.[7] have concluded that high-moisture corn should be dried to 23 per cent (db) and tempered for 40 min in order to maintain quality and to reduce energy consumption. Mostly empirical and semi-empirical methods have been used for the simulation of drying behaviour of corn. Doymaz and Pala [8] have taken into account two such types of models to simulate thin layer dry- ing of corn and found that the page equation pro- vides a better fit than the single exponential model. Drying curve for supersweet corn has been correlated JPME253 © IMechE 2009 Proc. IMechE Vol. 223 Part E: J. Process Mechanical Engineering