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Drying of food materials like ragi, wheat, rice, seeds is gaining importance in recent years. Many types of driers are available in practice and fluidized bed driers are one among them. It has many advantages like (i) high degree of contact between solids and gases (ii) very high heat and mass transfer rates (iii)better temperature control (iv) absence of moving parts, rotating seals and easy maintenance (v)good mixing over other driers. In the present investigation a continuous drying of food grain ragi has been studied. The experimental set up consists of a main body, a annular tube fixed at the centre of the main body in which the drying takes place, a disengaging section and the auxiliaries like rotameter, compressor, manometer etc.A known amount of moisture content in ragi is fed and it is dried in the annular circulation fluidized bed. The non-ideal unsteady state stirred tank reactor equation found to fit the model. The mass transfer is predominantly controlled by gas film diffusion at lower air flow rates (4.5 to 7 cm/s) and internal diffusion at high flow rate (7 to 13 cm/s).

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RANGASAMY PARTHIBAN, M.Tech.,Ph.D.(Environmental Technology), Professor & Head, Department of Chemical Engineering, Sri Venkateswara College of Engineering, Sriperumbudur, India.

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