Question

Calculate the heat transfer rate per m² area by radiation between the surfaces of two long cylinders having radii 100 mm and 50 mm respectively. The smaller cylinder being in the larger cylinder. The axes of the cylinders are parallel to each other and separated by a distance of 20 mm. The surfaces of inner and outer cylinders are maintained at 127°C and 27°C respectively. The emissivity of both the surfaces is 0.5. 

Assume the medium between the two cylinders is non-absorbing

Answer 1

r₁ = 50 mm = 0.05 m ; r₂ = 100 mm = 0.1 m, T₁ = 127 + 273 = 400 K, 

T₂ = 27 + 273 = 300 K, ε₁ = ε₂ = 0.5 

The heat transfer between two concentric or eccentric cylinders is given by

Substituting the values, we have