Rotary Drying This method of drying has been researched at the IRRI in Philippines and also at the AIT in Thailand. Small dryers for farm use were developed at the IRRI as reported by Espanto et al. The interior of the drum is fitted with flights to facilitate mixing and uniform heat transfer. The drum is rotated manually. An indirect-heated dryer is constructed from a 2001 oil drum also mounted over a stove.
Air is passed through the drum by a fan.
The performance of both dryers was very similar. With paddy, milling quality was improved relative to sun drying but the viability of the grain was greatly reduced due to the high temperatures attained at the drum surface. When grain is irradiated by electromagnetic energy high temperature potentials are generated between the interior and surface of individual grains. Moisture therefore migrates to the surface where it evaporates to the surrounding air. The rate of airflow necessary is that required to absorb the moisture and not as the provider of latent heat.