1. Two tonnes of paddy with 22% moisture content (wb) are to be dried to 13% moisture content (db). Calculate the weight of bone-dry product and water evaporated during the drying.... 1. Two tonnes of paddy with 22% moisture content (wb) are to be dried to 13% moisture content (db). Calculate the weight of bone-dry product and water evaporated during the drying. 2. Two tonnes of wheat grains are to be dried from 20% (wb) moisture content to 12% (wb) in 2 hrs using a mechanical dryer. How much air and heat will be required to dry the grains? 3. It is desired that 4 tonnes of parboiled paddy is to be dried on the open floor under the sun from 30% to 14% moisture content (wb) during 16 hrs effective drying time. The average rate of water removal is 0.5 kg/m2.hr, calculate the floor area required for sun drying. 5. A sample of wheat grains was dried in a thin layer at 65 °C temperature. The moisture content at 0, 1, and 2 hrs interval were 25.30, 18.50, and 15.90% (db), respectively. Compute the EMC, Me, and the value of constant k in drying rate equation. 6. Rough rice was dried at 50 °C and 60% relative humidity. The moisture content at time 3 and 5 hrs are 12.0 and 10.0%, respectively. If the drying rate constant be 0.49 per hour, calculate the equilibrium moisture content of the sample. Read more

Steps to Solve

1. Define Weight of Bone-Dry Product for Paddy Drying Calculate the weight of bone-dry paddy from the initial and final moisture content.

   • Initial weight of paddy: 2 tonnes = 2000 kg
   • Initial moisture content (wb): 22%
   • Final moisture content (db): 13%

   The formula for bone-dry weight is given by: $$ \text{Bone-dry weight} = \frac{\text{Wet weight} \times (100 - \text{wb})}{100 - \text{db}} $$

2. Calculate Water Evaporated during Paddy Drying Find the total water content before and after drying to determine the water evaporated.

   • Water evaporated: $$ \text{Water evaporated} = \text{Initial water content} - \text{Final water content} $$ where, $$ \text{Initial water content} = \text{Weight} \times \frac{\text{wb}}{100} $$ $$ \text{Final water content} = \text{Weight} \times \frac{\text{db}}{100} $$

3. Calculate Air and Heat Required for Wheat Drying For the second problem, calculate the air and heat required to reduce wheat moisture from 20% to 12%.

   • Water evaporated: $$ \text{Water evaporated} = \text{Weight} \times \left( \frac{\text{Initial wb} - \text{Final wb}}{100} \right) $$ Substitute the values.

4. Calculate Floor Area for Sun Drying of Parboiled Paddy For the third problem, calculate the floor area required given the drying rate.

   • Use the formula: $$ \text{Area} = \frac{\text{Water evaporated}}{\text{Water removal rate} \times \text{Drying time}} $$ where, $$ \text{Drying time} = 16 \text{ hours} $$

5. Calculate EMC, Me, and Constant k for Wheat Drying For the fifth problem, use the moisture content at different times to calculate the equilibrium moisture content (EMC), moisture content (Me), and drying constant (k).

   • EMC and Me can be determined based on moisture change.
   • The constant k is derived from the drying rate equation.

6. Calculate Equilibrium Moisture Content for Rough Rice For the rice drying, calculate equilibrium moisture content using the drying rate constant.

   • The relatively simple method utilizes the change in moisture over the drying time to find equilibrium.