# Thermodynamics Questions and Answers – One Dimensional Steady Isentropic Flow and Choking-2

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This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “One Dimensional Steady Isentropic Flow and Choking-2”.

1. The discharge is maximum when Mach number is
a) 0
b) 1
c) 2
d) infinity

Explanation: This comes when we differentiate discharge with respect to M.

2. Which of the following relation is correct?
a) (dA)/A = (M + 1)*(dV/V)
b) (dA)/A = (M – 1)*(dV/V)
c) (dA)/A = (M2 + 1)*(dV/V)
d) (dA)/A = (M2 – 1)*(dV/V)

Explanation: Taking isentropic flow and using continuity equation. we get this relation.

3. Where do we have the value of Mach number as 1 ?
a) at the start of flow
b) at the throat
c) at the end of flow
d) everywhere along the nozzle or diffuser

Explanation: At throat we have area as constant which is required for M=1.
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4. Which of the following statement is true about velocity of gas when it is subsonic?
a) it is subsonic before throat
b) becomes sonic at throat
c) becomes supersonic till its exit
d) all of the mentioned

Explanation: This is the case when convergent-divergent duct acts as nozzle.

5. When are properties at throat termed as critical?
a) when M=1
b) discharge is maximum
c) nozzle is choked
d) all of the mentioned

Explanation: For a choked nozzle, we have critical properties at throat.

6. Which of the following relation is correct?(asterik * indicates critical properties)
a) T*/T = 2/ɣ
b) T*/T = 2/(ɣ-1)
c) T*/T = 2/(ɣ+1)
d) T*/T = 2/(ɣ-2)

Explanation: This is the critical temperature ratio.

7. For diatomic gases, critical pressure ratio is equal to
a) 0.528
b) 0.628
c) 0.728
d) 0.828

Explanation: Putting ɣ=1.4 in critical pressure ratio relation we get this.

8. Which of the following statement is true?
a) M is proportional to only velocity
b) M tends towards infinity at low speeds
c) both of the mentioned
d) none of the mentioned

Explanation: Mach number is not proportional to velocity alone and tends towards infinity at very high speeds.

9. Which of the following is correct?
a) when M<1, M*>1 and when M>1, M*<1
b) when M=0, M*=0 and when M=1, M*=1
c) both of the mentioned
d) none of the mentioned

Explanation: When M<1, M*<1 and when M>1, M*>1.

10. At the choking limit, nozzle passes the ____ mass flow.
a) maximum
b) minimum
c) constant
d) all of the mentioned

Explanation: This occurs at the throat.

11. The condition of supersonic flow through throat with adiabatic conditions is called the design pressure ratio of nozzle.
a) true
b) false

Explanation: The condition of supersonic flow through throat with isentropic conditions is called the design pressure ratio of nozzle.

12. Which of the following statement is true?
a) shocks occur when flow is supersonic
b) after the shock, flow becomes subsonic
c) rest of the diverging portion acts as diffuser
d) all of the mentioned

Explanation: Shocks is a highly irreversible phenomenon.

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