Q1: 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%).

ANS:C - 71 min

To solve this problem, we can use the concept of drying time ratios. Given:

• Initial moisture content: 50%
• Final moisture content: 15%
• Critical moisture content: 10%
• Equilibrium moisture content: 5%

First, we calculate the drying time ratio for the first drying period: Drying time ratio=Initial moisture content−Critical moisture contentInitial moisture content−Equilibrium moisture contentDrying time ratio=Initial moisture content−Equilibrium moisture contentInitial moisture content−Critical moisture content​ Drying time ratio=50%−10%50%−5%=40%45%=44.5=89Drying time ratio=50%−5%50%−10%​=45%40%​=4.54​=98​ Now, we can use this drying time ratio to find the time it takes to dry from 15% to 10% moisture content: Time taken for second drying period=Drying time ratio×Time taken for first drying periodTime taken for second drying period=Drying time ratio×Time taken for first drying period Time taken for second drying period=89×6 hoursTime taken for second drying period=98​×6 hours Time taken for second drying period=89×6×60 minutesTime taken for second drying period=98​×6×60 minutes Time taken for second drying period=89×360 minutesTime taken for second drying period=98​×360 minutes Time taken for second drying period=320 minutesTime taken for second drying period=320 minutes Thus, it will take an additional 320 minutes−6 hours=320 minutes−360 minutes=−40 minutes320 minutes−6 hours=320 minutes−360 minutes=−40 minutes. This negative result indicates that it will actually take less time to dry from 15% to 10% moisture content compared to the initial drying period. This result seems unlikely, so let's recheck the calculations. 89×360 minutes=320 minutes98​×360 minutes=320 minutes So, it should actually take 320 minutes.