Agricultural Engineering and Agro-products Processing towards Mechanization and Modernization in Rural Areas“at Nong-Lam University, Ho Chi Minh City, 11-12 December 2003.
Lecturers, Faculty of Agricultural Engineering and Technology, Nong-Lam University Ho Chi Minh City, Vietnam. E-mailphhien@hcm.vnn.vn
INTRODUCTION
In Vietnam, over the past 20 years, the simple flat-bed dryer has been accepted anddeveloped into the foremost dryer for reducing post-harvest paddy losses due to adverserainy weather, with about 3000 units of capacities from 4 to 8 tons per batch.Goodfeatures of these dryers are: fairly high capacity, good grain quality, low drying cost, easyto install and operate.Nevertheless, as simplest dryers with a major drawback of non-uniformity in final grain moisture content, they have to be changed to meet the needs for more-mechanized dryers at rice milling centers.
The series of SRA dryers (RA is abbreviation for Reversible-Air, S is drying in Vietnamese) have been designed to serve the above change. The research began in 1999 at Nong-Lam University (NLU, formerly University of Agriculture and Forestry) with alaboratory model for basic information about drying characteristics of various crops with reversible airflow. Next, a pilot 1.5-ton/batch SRA dryer was designed and tested with paddy and coffee. Finally, the dryer was scaled up to different models, of 2; 4; 6; 8; 10;and 12 tons per batch.Twenty five SRA units have been applied successfully in various Provinces of Vietnam; of which 8 units have each dried 500-1500 tons in the past 3 years. Features drawn from testing and using these dryers are: a) Saving of land space; b) More mechanized, meaning lessuse of manuallabor; c) Multi-crop use, in cluding high-moistureproducts such as coffee, sliced cassava, longan… , and d) The investment and drying costare not higher compared to a flat-bed dryer of similar capacity. Successful applications ofthese SRA have been reported elsewhere (Nguyen Hung Tam et.al., 2002; Phan Hieu Hien,2003)
The unique feature of these dryers, is that the drying is reversed only once, which makes the process different from other dryers reported in the literature with periodic air reversal,say, every 2 hours.Less air reversal means less intervention by manual labor, which in turn contributes to lower drying cost. But this once-only air reversal should ensuremoisture uniformity for users’ acceptance.
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