This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Availability-1”.
1. When we obtain useful work during a process in which a finite system undergoes a change of state, when should that process terminate?
a) when the pressure of system equals the pressure of surroundings
b) when the temperature of system equals the temperature of surroundings
c) when the system has reached the dead state
d) all of the mentioned
View Answer
Explanation: The process goes on until the system reaches the dead state.
2. The availability(A) of a given system is defined as the ____ work that is obtainable in a process in which system comes to equilibrium with its surroundings.
a) useful work
b) maximum useful work
c) minimum useful work
d) none of the mentioned
View Answer
Explanation: Maximum useful work is given by total work minus pdV work.
3. Availability is a composite property.
a) true
b) false
View Answer
Explanation: This is because it depends on the state of both the system and surroundings.
4. Availability function for a steady flow system is given by
a) H+TS+(m*V*V/2)+(m*g*z)
b) H-TS+(m*V*V/2)+(m*g*z)
c) H-TS-(m*V*V/2)-(m*g*z)
d) H-TS-(m*V*V/2)+(m*g*z)
View Answer
Explanation: This term comes very frequent and is considered as availability function for a steady flow system.
5. Availability function for a closed system is given by
a) u-pv-Ts
b) u+pv+Ts
c) u-pv+Ts
d) u+pv-Ts
View Answer
Explanation: This term comes very frequent and is considered as availability function for a closed system.
6. Which of the following is true for an internal combustion engine?
a) the reactants are in pressure and temperature equilibrium with the surroundings
b) the products are in pressure and temperature equilibrium with the surroundings
c) both of the mentioned
d) none of the mentioned
View Answer
Explanation: This is true if the products are cooled to atmospheric temperature To before being discharged from the engine.
7. The Helmholtz function F is given by
a) U-TS
b) U+TS
c) -U-TS
d) -U+TS
View Answer
Explanation: Helmholtz function F is a property which is defined by the relation F=U-TS.
8. Which of the following statement is true?
a) maximum work is done when process is reversible
b) if the process is irreversible, work is less than the maximum
c) W<=(F1-F2)
d) all of the mentioned
View Answer
Explanation: W<=(F1-F2) when initial and final temperature of system is same as that of surroundings.
9. Gibbs function G is given by
a) G=H-TS
b) G=U+pV-TS
c) both of the mentioned
d) none of the mentioned
View Answer
Explanation: G=H-TS and H=U+pV.
10. If the process is irreversible, the useful work is less than the maximum.
a) true
b) false
View Answer
Explanation: Useful work is maximum for a reversible process.
11. Find the availability when 100 kW is delivered at 500 K when the ambient temperature is 300 K.
a) 20 kW
b) 30 kW
c) 40 kW
d) 50 kW
View Answer
Explanation: Φ = W(revHE) = [1-(To/T)]Q = [1-(300/500)](100) = 40 kW.
12. A control mass gives out 10 kJ of energy in the form of heat transfer at 500°C. Find the change in availability of the control mass.
a) −4.14 kJ
b) −5.14 kJ
c) −6.14 kJ
d) −7.14 kJ
View Answer
Explanation: ∆Φ = -[1-(To/Th)]Q = -[1-(298.15/773.15)](10) = −6.14 kJ.
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