Chemegate
Home/Practice Tests/PYQ Archive/Heat Transfer

GATE 2026 Chemical Engineering, Q53 · Heat Transfer

The correct answer is 15.5 to 16.5.

Question

A pipe with outer diameter of 0.02 m carries hot water at a surface temperature of 70°C.70°C. It is covered with two 0.01 m-thick layers of insulation: felt (k = 0.12 W m−1°C−1,m⁻¹ °C⁻¹, inner layer) and asbestos (k = 0.15 W m−1°C−1,m⁻¹ °C⁻¹, outer layer), exposed to ambient air at 20°C20°C with a convection coefficient of 3 W m−2°C−1m⁻² °C⁻¹ at the outer surface. At steady state, neglecting radiation, the heat loss (in W m−1)m⁻¹) is _____ (rounded off to two decimal places).

Official answer: 15.5 to 16.5

Why

GATE 2026 official key: 15.5 to 16.5. Per-length resistances: felt ln(2)/(2π⋅0.12)≈0.92,ln(2)/(2π\cdot 0.12)\approx 0.92, asbestos ln(1.5)/(2π⋅0.15)≈0.43,ln(1.5)/(2π\cdot 0.15)\approx 0.43, convection 1/(2π⋅0.03⋅3)≈1.77;1/(2π\cdot 0.03\cdot 3)\approx 1.77; total ≈3.12\approx 3.12 m·K/W. q' =50/3.12≈16.0= 50/3.12 \approx 16.0 W/m.

Explanation cross-checked for consistency. Final answer matches the official IIT answer key.

Heat Transfer Topic Guide →More Heat Transfer PYQs →Take the Full GATE 2026 Test →