# Separation Processes Questions and Answers – Multiphase Systems

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This set of Separation Processes Multiple Choice Questions & Answers (MCQs) focuses on “Multiphase Systems”.

1. What is the third phase in all the two phase systems?
b) The interface
c) The container
d) The atmosphere

Explanation: The third phase is the container which selected as inert for separation purposes.

2. How to separate vapor-liquid-liquid system?
a) Fractional distillation
b) Fractional crystallization
c) Zone melting
d) Three phase isothermal flash

Explanation: A three phase isothermal flash is used to separate vapor-liquid-liquid system.

3. Why are calculations for three phase flash difficult?
a) Because of strong dependency of K values on liquid phase composition when two immiscible liquids are present
b) Because of strong dependency of K values on vapor phase composition when two immiscible liquids are present
c) Because of strong dependency of K values on liquid phase composition when two miscible liquids are present
d) Because of strong dependency of K values on liquid phase composition when three immiscible liquids are present

Explanation: The calculations of three phase flash are difficult due to strong dependency of K values on liquid phase composition when two immiscible liquids are present.

4. What is the enthalpy balance for three phase system?
a) hFF + Q =hvV + hLL(1) + hLL(2)
b) hFF =hvV + hLL(1) + hLLL(2)
c) hFF – Q =hvV + hL(1) + hLLL(2)
d) hFF + Q =hvV + hLL + hLLL

Explanation: The correct enthalpy balance is hFF + Q =hvV + hLL(1) + hLL(2).

5. The calculations of multiphase system are made by:
a) Graph
b) Hand calculations
c) Trial and error
d) Process simulators

Explanation: Calculations of multiphase system are made by process simulators.

6. If at a certain pressure the vapor pressure of water is 4.74pisa and the mole fraction of water is 0.923, find out the crystallizer pressure.
a) 2.5pisa
b) 4.38pisa
c) 4.56pisa
d) 4.76pisa

Explanation: Roult’s law is used P=psxh20. Hence P=4.74*0.923=4.38pisa.

7. If at a certain pressure the vapor pressure of water is 8pisa and the mole fraction of water is 0.9, find out the crystallizer pressure.
a) 0.64pisa
b) 7.2pisa
c) 0.66pisa
d) 0.81pisa

Explanation: Roult’s law is used P=psxh20. Hence P=8*0.9=7.2pisa.

8. If at a certain pressure the vapor pressure of water is 6pisa and the mole fraction of water is 0.7, find out the crystallizer pressure.
a) 3.3pisa
b) 3.5pisa
c) 3.96pisa
d) 4.2pisa

Explanation: Roult’s law is used P=psxh20. Hence P=6*0.7=4.2pisa.

9. If at a certain pressure the vapor pressure of water is 2pisa and the mole fraction of water is 0.9, find out the crystallizer pressure.
a) 0.45pisa
b) 1.8pisa
c) 3.6pisa
d) 0.81pisa

Explanation: Roult’s law is used P=psxh20. Hence P=2*0.9=1.8pisa.

10. If at a certain pressure the vapor pressure of water is 10pisa and the mole fraction of water is 0.8, find out the crystallizer pressure.
a) 5pisa
b) 6pisa
c) 7pisa
d) 8pisa 