Page 2 012 - : Open book section (75) 1. Apple juice is manufactured by adding w
ID: 1027735 • Letter: P
Question
Page 2 012 - : Open book section (75) 1. Apple juice is manufactured by adding water and citric acid to the apple juice concentrate. The concentrate contains 60% (w/w) sugar, and 0.1% citric acid. How much concentrate, water and pure citric acid powder is needed to formulate 1000 kg juice containing 15% (w/v) sugar and 0.2% (w/v) citric acid. (15) 2. 1000 liter/minute of apple juice (density 1.2 kg/liter, specific heat 3.8 kJ/kg) is to be pasteurized by heating from 4 °C to 74 °C. This is accomplished by using at 120 °C. The flow rate of steam was set at 130 kg/minute (Latent heat of steam is 2400 kJ/kg, specific heat of water and steam are 4.18 kJ/kg C and 2 kJ/kg oC). What will be the outlet temperature of the steam/hot water? (10) 3. In problem 2, once the apple juice (1000 liter/min, density 1.2 kg/liter, specific heat is 3.8 kJ/kg °C) exits from the pasteurizer, it is held at a temperature of at least 72 °C for 15 second to ensure a complete inactivation of bacteria. This is accomplished by passing the apple juice through a holding tube that is essentially a long stainless steel tube covered with an insulation. The tube chosen for this operation has an inside diameter of 4 cm and has a thickness of 10 mm. What should be the length of the tube to ensure that the juice resides in the holding tube for a minimum of 15 s? The stainless steel tube has a thermal conductivity of 64 W/m C. The insulator surrounding the tube is 4 cm thick. The 52Explanation / Answer
Apple juice concentrate contains sugar, citric acid and water. So there are 3 components.
Let x= mass of concentrate, y= mass of water and z= mass of citric acid
Hence three balance equations can be written, one for sugar, one for water and one for citric acid
Concentrate contains 60% sugar, 0.1% citric acid and balance is 100-(60+0.1)= 39.9% water
Apple juice contains 15% sugar, 0.2% citric acid and balance is 100-(15+0.2)= 84.8% water
Since Appled juice is formulated by addition of water and citric acid to apple juice concentrate.
Writing sugar balance
Mass of sugar in concentrate= mass of sugar in 1000 kg
Hence x*60/100 = 1000*15/100, x= 250 kg of concentrate
Next writing citric acid balance
Mass of citric acid in concentrate= mass of citric acid in 1000 kg + mass of citric acid added
=250*0.1/100 = 100*0.2/100+z, z=0.05 gm of citric acid
Writing water balance
Mass of water in concentrate= mass of water in 1000Kg+ mass of water added
250*39.9/1000= 1000*84.8/100 +x , x= 14.95 gm
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