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# Separation Processes MCQ’s – Energy, Entropy and Availability Balance

1 - Question

Which of the following is a correct equation of energy balance?

a) ∑out of system nh+Q+Ws – ∑insystem nh+Q+Ws=0

b) ∑out of system nh+Ws- ∑insystem nh+Q+Ws=0

c) ∑out of system nh+Q+Ws – ∑insystem nh+Ws=0

d) ∑out of system nh+Ws – ∑insystem nh+Ws=0

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Answer: aExplanation: Heat giver or taken and shaft work also must be taken into account.

2 - Question

Which of the following is a correct equation for entropy balance?

a) ∑out of system (nS+Q/Ts) – ∑insystem (nS)=0

b) ∑out of system (nS+Q/Ts) – ∑insystem (nS+Q/Ts)=ΔSr

c) ∑out of system (nS) – ∑insystem (nS+Q/Ts)=ΔSr

d) ∑out of system (nS+Q/Ts) – ∑insystem (nS+Q/Ts)=0

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Answer: bExplanation: Initial entropy minus final entropy gives the difference in the entropy.

3 - Question

What is the formula for minimum work of separation?

a) ∑out of system (nb) – ∑insystem (nb)=Ws

b) ∑out of system (nb) – ∑insystem (nb)=0

c) ∑out of system (nb) – ∑insystem (nb)= ΔSr

d) ∑out of system (nb) – ∑insystem (nb)=Δnb

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Answer: aExplanation: The difference of the molar availabilities gives the minimum work of separation.

4 - Question

What is the formula for efficiency?

a) η = Wmin /(LW + Wmax)

b) η = Wmax /(LW + Wmax)

c) η = Wmin /(LW + Wmax)

d) η = Wmin /( Wmax)

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Answer: cExplanation: Only Wmin is considered and lost work is considered.

5 - Question

What is the maximum of energy converted to shaft work if stream is taken to reference state?

a) Gibbs energy

b) Availability function

c) Entropy

d) Change in entropy

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Answer: bExplanation: b = h – tS the availability function which the maximum energy converted to shaft w

6 - Question

What is the formula for lost work?

a) LW = h- TΔS

b) LW = T0 – TΔSirr

c) LW = T0 ΔSirr

d) LW = T0 – Sirr

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Answer: cExplanation: The multiplication in the absolute temperature and the change in entropy give the lost work.

7 - Question

What is the magnitude of lost work not dependent upon?

a) Process irreversibilities

b) Fluid friction

c) Mass transfer due to finite concentration

d) Mass transfer due to finite temperature driving forces

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Answer: dExplanation: Mass transfer is not affected by finite temperature driving forces; hence it is a wrong option.

8 - Question

Why does the reduce in lost work have limitation?

a) Equipment size decreases

b) Equipment size increases

c) Flow rate decreases

d) Flow rate increases

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Answer: bExplanation: As the driving forces decrease to reduce lost work, the equipment size increases

9 - Question

What is the lost work is absolute temperature is 303K and the change in entropy is 1000KJ/h-k

a) 697KJ/h-k

b) 303000KJ/h

c) 3030KJ/h

d) 30300KJ/h-k

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Answer: bExplanation: LW = T0 ΔSirr.

10 - Question

If the minimum work of separation is 100KJ and the lost work is 1000KJ, what is the efficiency of separation process?

a) 10%

b) 11%

c) 9.09%

d) 11.11%

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Answer: cExplanation: η = Wmin/(LW + Wmax).