Solar rice drying project (Thailand)
1984
Exell, R.H.B. | Sompong Boonthumjinda
A simple inexpensive solar rice dryer for use in the wet season had been designed and tested. The project was divided into two phases: Phase I in which tests were undertaken on the campus of the Asian Institute of Technology to ascertain the effects of modifications in the design, and Phase II in which the dryers were field-tested on rice farms in the central plain of Thailand. The dryer used for the tests on campus was divided into eight separate compartments for performing several different tests simultaneously. It used solar heated air passing by natural convection through a bed of paddy, and heat from solar radiation incident on the top of the bed. The paddy inside the dryer was fully protected from rain. Tests in the wet season found that drying started simultaneously at the top and bottom of the bed, while the middle layer dried slowest. The optimum thickness of the bed was 100 mm, and drying took one to four days, depending on the weather. The use of a chi1335mney increased the air flow through the bed significantly, and reduced the drying time by about 10 percent. Periodic stirring of the bed of paddy reduced the drying time by about one half. The solar rice dryers tested on farms had a capacity of one ton of paddy. They were made of bamboo poles and clear plastic sheet, and cost about US$ 150 to build. The performance of the dryers in the field was the same as that found in the campus tests. Shortcomings in the dryers revealed by the field tests included: degradation of the plastic sheet the need for a higher capacity than one ton per batch, and rehumidification of the paddy in the bed at night during wet wea
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