🎯 NPCIL/PSU Mechanical Engineering Interview Experience

🗓 Date: 13th June 2025
📍 Venue: [Location not specified]
🧪 Mode: Technical | Conceptual | Application-Oriented
👨‍🔬 Interview Focus: Fluid Mechanics, Heat Transfer, Strength of Materials, Engineering Drawing, Manufacturing

🌊 1. Fluid Mechanics – Pressure in Stratified Fluids

Scenario: A container is filled with two immiscible fluids:

• Water (height = h) on top
• Mercury (height = h) at the bottom

Questions & Concepts:

• a) Draw the Pressure vs. Depth diagram:
  • Linear increase through water
  • Steeper gradient through mercury due to higher density
• b) Calculate:
  • Pressure at the water–mercury interface:
    Pinterface=ρwater⋅g⋅hP_{\text{interface}} = \rho_{\text{water}} \cdot g \cdot hPinterface​=ρwater​⋅g⋅h
  • Pressure at the bottom of the container:
    Pbottom=Pinterface+ρHg⋅g⋅hP_{\text{bottom}} = P_{\text{interface}} + \rho_{\text{Hg}} \cdot g \cdot hPbottom​=Pinterface​+ρHg​⋅g⋅h
• c) What happens upon stirring/mixing?
  • Leads to a uniform mixture with average density
  • Pressure profile becomes linear from top to bottom

🔥 2. Heat Transfer – Cooling of a Hot Sphere

Problem Statement:
A spherical metal ball (d, 800°C) is removed from a furnace and placed in:

a) Still Air

• Asked to plot Temperature vs. Time curves for:
  • Surface Temperature (drops rapidly)
  • Center Temperature (lags due to internal conduction)
  • Average Temperature

b) Water

• Comparative graph requested
• Key Insight:
  • Water has a higher heat transfer coefficient
  • Rapid drop in temperature at both surface and center

🧱 3. Strength of Materials – Stress-Strain Behavior

a) Stress–Strain Curve for Mild Steel

• Drawn and explained:
  • Proportional limit
  • Elastic limit
  • Yield point
  • Ultimate tensile strength (UTS)
  • Fracture point
• Discussion on types of steels:
  • Low, Medium, High Carbon Steels
  • Alloying elements: C, Mn, Cr, Ni, Mo

📘 Taught in Chayan Batch 2.0 – SOM Lecture 01

✏️ 4. Engineering Drawing – Orthographic Views

Task:

• Draw Top and Front Views of a duster
• Identify the Projection Method: First Angle
• Explained the logic behind view placement

🧱 5. Force Analysis – Plate Fixed in L-Shaped Wall

Setup: Plate fixed inside an L-type wall with force F applied at the bottom.

Discussion:

• Stress types:
  • Bending stress
  • Shear stress
  • Tensile/Compressive stress at fixed end
• Insight into reaction forces and stress distribution

⚙️ 6. Manufacturing – Machine Tools & Fasteners

• Q: Which tool is used for thread cutting?
  • Lathe Machine with single-point cutting tool
  • Also mentioned taps and dies for internal/external threading
• Bonus Rapid-Fire:
  • M10 × 2 in bolt thread:
    • M10 = 10 mm nominal diameter
    • 2 = 2 mm thread pitch

✅ Final Reflections

This interview was highly visual, with emphasis on:
✔️ Diagrammatic understanding
✔️ Real-life engineering scenarios
✔️ Connecting theory with design applications

📌 Be prepared to:

• Sketch quickly and accurately
• Justify assumptions using equations and logic
• Explain practical relevance of classroom concepts

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