Engineering Questions with Answers - Multiple Choice Questions
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
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: 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)
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: 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%
View Answer
Explanation: η = Wmin/(LW + Wmax).