Freeze-drying is a process used to preserve food. If strawberries are to be free

Question

Freeze-drying is a process used to preserve food. If strawberries are to be freeze-dried, then they would be frozen to -80.00 °C and subjected to a vacuum of 1.00 mtorr. As the water is removed, it is frozen to a cold surface in the freeze-drier. If 150 mL of water has to be removed from a batch of strawberries, how much energy would be required?

_____________ kJ

At any given time, how much water is in the atmosphere if the volume of the freeze-drier is 5 liters?

__________ g of water

If it takes one hour to remove one mL of water, how long will it take to freeze-dry the strawberries?

________ hours

Explanation / Answer

taking basis of 100 kg of strawberry as standard intially, the calculation as follows

100 kg of strawberry contains moisture of = 100*0.172g of water = 17.2 kg moisture

and 100*(1-0.172) = 82.8 kg of dry strawberry

Latent heat of evaporation = 2257 kJ kg-1(at 100 °C)

so heat necessary to supply = 17.2 x 2257 = 3.88 x l04 kJ

If freeze drier is 5 litres then 5*0.172 = 860 gm of moisture (water)

If it takes 1 hr for 1 ml of water then total of 860 hrs is required to remove 860 gm of water

Related Questions

Navigate

• Browse (All)
• Browse F
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.