Mass Transfer Questions and Answers – Time period Calculation in Batch Drying

This set of tricky Mass Transfer Questions & Answers focuses on “Time period Calculation in Drying”.

1. 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.
a) 20 sec
b) 40 sec
c) 60 sec
d) 80 sec
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2. Find the period if the initial and the final moisture content are 60% and 40%. Also the critical moisture content is 30%.
a) Constant rate period
b) Falling rate period
c) Unsaturated period
d) None of the mentioned
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3. Find the period if the initial and the final moisture content are 50% and 20%. Also the critical moisture content is 30%.
a) Constant rate period
b) Falling rate period
c) saturated period
d) None of the mentioned
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4. At the constant drying period of a batch process, the rate of drying varies accordingly.
a) True
b) False
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5. Find the change in moisture content from the given data
Given data:
Time for drying= 6 sec
Area * Constant rate = 8 kg per sec
Weight of wet solid = 100 kg
a) 0.21
b) 0.12
c) 0.48
d) 0.84
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6. 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)
a) 35
b) 30
c) 60
d) None of the mentioned
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7. 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)
a) 45
b) 50
c) 60
d) None of the mentioned
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8. Falling rate period of a batch process starts at
a) Saturated drying surface
b) Unsaturated drying surface
c) Both unsaturated and saturated region
d) None of the mentioned
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9. If the time taken for the moisture removal is obtained from the formula
Time = Ss(Xc – Xe)/ Nc * A ln ((X1-Xe)/(X2-Xe)) then the falling curve will be curves symmetrically
Where, Ss= Wet solid weight
Xc,Xe- constant & equilibrium moisture content
X1,X2 – initial and final moisture content
a) True
b) False
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10. There will be a change in the rate of drying of a batch process after the constant drying process.
a) True
b) False
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11. Find the Constant rate representation

a) X
b) Y
c) Z
d) A
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12. Find the representation of critical moisture content value

a) A
b) B
c) Z
d) Y
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13. Find the equilibrium content value

a) A
b) B
c) C
d) Y
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14. Falling rate period of the batch drying curve = _______ + ___________
a) Internal movement, unsaturated surface drying
b) Internal movement, saturated surface drying
c) External movement, unsaturated surface drying
d) External movement, saturated surface drying
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15. Find the region if the final and the initial moisture content are 40% and 30% (Dry basis) and the critical moisture content is 45%.
a) Constant rate
b) Falling rate
c) Internal movement
d) None of the mentioned
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