Calculation Methods for Constant-Rate Drying Period

6 CALCULATION METHODS FOR CONSTANT-RATE DRYING PERIOD 

Introduction. Probably the most important factor in drying calculations is the length of time required to dry a material from a given initial free moisture content Afi to a final moisture content Xj - For drying in the constant-rate period, we can estimate the time 

Method using drying curve. To estimate the time of drying for a given batch of material, the best method is based on actual experimental data obtained under conditions where the feed material, relative exposed surface area, gas velocity, temperature, and humidity are essentially the same as in the final drier. Then the time required for the constant-rate period can be determined directly from the drying curve of free moisture content versus time. 

EXAMPLE 9.6-1. Time of Drying from Drying Curve A solid whose drying curve is represented by Fig. 9.5-la is to be dried from a free moisture content Xj = 0.38 kg iiiOPag dry solid to Xj = 0.25 kg H20/kg dry solid. Estimate the time required. 

Method using rate-of-drying curve for constant-rate period. Instead of using the drying curve, the rate-of-drying curve can be used. The drying rate R is defined by Eq. (9.5-3) as 

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Sec. 9.6 Calculation Methods for Constant-Rate Drying Period... 

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