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A solid is being dried in the linear drying rate regime from moisture content X<sub>o</sub> to X<sub>F</sub>. The drying rate is zero at X = 0 and the critical moisture content is the same as the initial moisture X<sub>o</sub>. The drying time for M = (L<sub>s</sub>/AR<sub>c</sub>) is (where, L = total mass of dry solid, A = total surface area for drying R<sub>c</sub> = Constant maximum drying rate per unit area X = moisture content (in mass of water/mass of dry solids)

Correct Answer: MX<sub>o</sub> ln(X<sub>o</sub>/X<sub>F</sub>)

200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000 seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5 × 10-3 kg/m2.s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m2/1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid)

In a laboratory test run, the rate of drying was found to be 0.5 × 10-3 kg/m2.s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m2/kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is

A dryer is used for drying pears which has initial moisture content of 70 % (wet basis) and final moisture content of 5 % (wet basis). An experimental drying curve for the product indicates that the critical moisture content is 25 % (wet basis) and the time for constant drying is 5 min. Can you estimate the total drying time for product?

It takes 6 hours to dry a wet solid from 50% moisture content to the critical moisture content of 15%. How much longer it will take to dry the solid to 10% moisture content, under the same drying conditions? (The equilibrium moisture content of the solid is 5%).

A 25 cm × 25 cm × 1 cm flat sheet weighing 1.2 kg initially was dried from both sides under constant drying rate conditions. It took 1500 seconds for the weight of the sheet to reduce to 1.05 kg. Another 1 m × 1 m × 1 cm flat sheet of the same material is to be dried from one side only. Under the same constant drying rate conditions, the time required for drying (in seconds) from its initial weight of 19.2 kg to 17.6 kg is

"It is now expected that the variable production cost per unit and the selling price per unit will each increase by 10%, and fixed production cost will rise by 25%. What will be the new break even point?
Selling price - Rs 6 per unit
Variable production cost - Rs 1.20 per unit
Variable selling cost - Rs 0.40 per unit
Fixed production cost - Rs 4 per unit
Fixed selling cost - Rs 0.80 per unit
Budgeted production and sales for the year are 10,000 units."

Find the initial moisture content for the batch process if the final moisture content is 25% (dry basis) and the constant moisture content is 40%. (Includes constant and falling rate period)

Find the final moisture content for the batch process if the initial moisture content is 75% (dry basis) and the constant moisture content is 40%. (Includes constant and falling rate period)

Find the moisture to be evaporated per kg of dried product if initial and final moisture content per kg of dry solid is 85% and 15%.

Find the time taken to dry 50% to 40% of moisture (dry basis) if critical moisture content is 30%. If the weight of the wet solid is 5 kg and the product of area and the constant rate is 0.5 kg/min.