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GATE 2019 ME (ME1) – Question 42

Heat Transfer · Convection: boundary layer, dimensionless parameters and correlations · 2 marks · Multiple choice

A 1 m constant-diameter pipe is heated with uniform wall heat flux. Flow enters hydrodynamically fully developed, is incompressible, steady and laminar. Bulk temperature rises from 0°C at inlet to 50°C at outlet. Wall temperatures at P, Q and R, respectively x = 0.4, 0.6, 0.8 m, are 50, 80 and 90°C. At which locations is flow thermally developed?

Diagram for GATE 2019 ME (ME1) question 42
  1. P, Q and R
  2. P and Q only
  3. Q and R only
  4. R only

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Show answer and explanation

Correct answer: (C) Q and R only

Explanation

Uniform heat flux gives bulk temperature $T_b=50x$ in °C. At P, Q and R it is 20, 30 and 40°C. Wall-minus-bulk differences are 30, 50 and 50°C. The constant difference at Q and R indicates thermally developed flow. **C**.