A very long rod (diameter = 25 mm, thermal conductivity = 400 W/m-K) extends from a surface at temperature of 121°C. The temperature of surrounding air is 25°C, convective heat transfer coefficient over the rod is 9 W/m²-K. What will be heat loss from the rod? [assume, π² = 10]

Question

Question

This question was previously asked in

BHEL Engineer Trainee Mechanical 24 Aug 2023 Official Paper

Answer 1

Concept:

For a very long rod, the heat loss is given by:

Where P is the perimeter and A_c is the cross-sectional area of the rod.

Given:

Diameter, d = 25 mm = 0.025 m

Thermal conductivity, k = 400 W/m·K

Convective heat transfer coefficient, h = 9 W/m²·K

Surface temperature, T_s = 121°C

Ambient temperature, T_∞ = 25°C

π² = 10

Calculation:

Perimeter,

Cross-sectional area,

Heat loss,

=