A membrane distillation unit is used to remove water and lactose from milk. In the unit warm milk flows through the inside of a bundle of fibres and a cold fluid which consists of water and lactose flows on the outside of the fibres. Some water and lactose from the milk pass through the fibre walls into the cold fluid and concentrated milk exits the unit.
(a) Draw the flowchart of the system with the information given below.
(b) Milk enters the unit at a rate of 220 mL/min and milk exits the unit at a rate of 215 mL/min. What is the rate of solution (in mL/min) and the rate of lactose (in mg/min) that passes into the cold fluid from milk if the entering concentration of lactose in milk is 2.30 mg/mL and the exiting concentration of lactose in milk is 1.70 mg/mL.
(c) If the cold fluid entering the unit at the rate of 1 L/min and exiting solution leaves at approximately the same rate, what is the concentration of lactose (mg/mL) in the cold fluid.
(d) What is the time required to reduce the concentration of lactose in 2 L of milk from an initial value of 2.50 mg/mL to a final value of 1.5 mg/mL. It can be assumed that the average rate of lactose removal is that calculated in (b) and the loss in total milk volume due to the removal of water into the cold fluid is negligible.