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J. Agric. Sci. Natur. Resour., Vol. 14(2), June -July 2007 www.sid.ir

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Study of rough rice drying process in fixed and fluidized bed conditions

M.H. Khoshtaghaza1, M. Sadeghi2 and R. Amirichayjan3

1Associate Prof. of Agricultural machinery engineering Dept. of Tarbiat Modares University, 2Assistant Prof. of Farm machinery Dept., Isfahan University of Technology, 3Assistant Prof. Farm machiney Dept. Buali sina

University

Abstract

Fluidized bed drying method is one of the most important new drying methods of agricultural materials. In this study the rough rice drying process by fixed and fluidized methods was compared based on thermal efficiency, drying rate and kernel fissuring percent. The experiments were conducted by a laboratory fluidized bed dryer with ability of the inlet air temperature and airflow rate control to operate in fixed and fluidized conditions. The rough rice samples were dried from 17.7 initial moisture content to 11% final moisture content (dry basis) at three temperatures of 40, 60 and 80C. The air velocity in fixed, semi-fluidized and fluidized bed conditions was 0.1, 1.1 and 3.5 m/s, respectively. The thermal efficiency of dryer was calculated based on the ratio of thermal energy utilized for evaporating water from the drying product to thermal energy supplied to the drying air. The maximum and minimum thermal efficiency of 22.84 and 3.3% were belonged to the fixed bed condition at 80C and the fluidized bed condition at 40C, respectively. The fixed bed condition was determined as the main factor influencing kernels fissuring, so that the maximum drying time of 280 minutes and the maximum kernel fissuring of 78% were measured in this condition at 80C. The minimum drying time of 40 minutes and the minimum kernel fissuring of 17% were belonged to the semi-fluidized bed condition at 80 and 40C, respectively. Keywords: Rough rice; Semi-fluidized; Thermal efficiency; Drying rate; Kernel fissuring

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