Materials and Energy Balances: Please draw process diagram(if possible) and plea
ID: 979549 • Letter: M
Question
Materials and Energy Balances:
Please draw process diagram(if possible) and please provide a detailed solution.
A 3-unit process (2 evaporators and 1 mixer) is used to concentrate salt water. 2000 kg/min of a NaCl/water solution of unknown mass fractions is flowed into an evaporator, where 500 kg/min of pure water is removed as vapor. The concentrated solution stream is sent to a mixer, where 1000 kg/min of a 20 wt% NaCl solution in water is added. The mixture is then sent to an evaporator, where 1000 kg/min pure water is removed as vapor. The final stream contains 50 wt% NaCl in water at an unknown total flow rate. Which of the following unit balances has 0 DOF?
Answer choices:
evaporator 1
mixer
evaporator 2
overall
none of the above
Explanation / Answer
Overall
Since in evaporagtor there are two unknown and water is evaporated in the first evaporator, so at the exit the composition is still unknown . In the mixer amount of Nacl is given and water is given and the amount coming from evaporator still remains unknown and after the evaporator, the mass fraction of Nacl is given and based on overall balane ony, NaCl at the intle of evaporator can be calculated.