Drying Basics and Principles

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Drying Basics and PrinciplesM Unit, CESD IRRI LB PhiliiIRRI Los Ba os, Drying process Moisture gradientTempering Tempering Heated air Drying and yglow temperature dryingDrying processyg I Preheating period Drying rate is slowly increasingincreasing only a very slight change in MC II Constant-rate period Drying rate is constant in time removal of surface water grain temperature is constantdtt energy used to evaporate water III Falling-rate period Drying rate declines over time-> Temperatures for Drying dddrying rate declines over time transfer of internal moisture to the surface Drying rate declinespaddy Seeds Maximum of 43 C For milling grain heats up (danger) for paddy grain starts at 18%g During constant-rate period: > 100 C During falling-rate period: < 55 C(depends on Drying system) Drying rateyg Stated in percent moisture removed per hourpp Affected by: Temperature and relative humidity of the Drying air Seeds: max.

– grain at the air inlet dries faster – moisture gradient unloading dry grains are 25 30 – - dry grains are . Top mixed with wet grains – Re-wetting -> cracks in dry grains 15 MC, % w.b 20 Middle Bottom Avg. • For even drying – sun drying: stir every 30 minutes iiifidbd 10 0 5 10 15 Drying time, h – mix grain in fixed bed dryers

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