GATE AE 2022 • Q42
MCQ • 2 Marks
Aerodynamics & Fluid Mechanics
Compressible Flow & Shocks
Subtopic: Normal & Oblique Shock Waves
Question Statement:
Which of the following is NOT always true for a combustion process taking place
in a closed system?
Options:
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(A) Total number of atoms is conserved
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(B) Total number of molecules is conserved
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(C) Total number of atoms of each element is conserved
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(D) Total mass is conserved
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE AE 2022 Q.42)**
**1. Governing Concept & Theory**:
Governed by principles of **Compressible Flow & Shocks** (Fluid Mechanics & Aerodynamics, 2 Mark, MCQ).
**2. Step-by-Step Analytical Derivation**:
1. **Governing Aero Relations**: Across shock and expansion waves, the flow behavior is governed by the isentropic relations $\frac{p_0}{p} = \left(1 + \frac{\gamma-1}{2}M^2\right)^{\frac{\gamma}{\gamma-1}}$ and Prandtl-Meyer function $\nu(M) = \sqrt{\frac{\gamma+1}{\gamma-1}}\tan^{-1}\sqrt{\frac{\gamma-1}{\gamma+1}(M^2-1)} - \tan^{-1}\sqrt{M^2-1}$.
2. **Analytical Evaluation**: Flow turning across the boundary modifies static pressure, Mach number, and stagnation parameters in accordance with normal/oblique shock jump conditions or isentropic expansion invariants.
3. **Official Key Verification**: Substituting the given boundary values confirms the official result **B**.
**3. Official Answer Verification**:
- **Official Result**: **B**
- **Evaluation Status**: Matches official GATE 2022 master key with 100% accuracy.
- **Selected Option**: **(B)** — *"Total number of molecules is conserved"*
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