Question

Liquid oxygen (boiling temperature = – 182°C) is to be stored in spherical container of 30 cm diameter. The system is insulated by an evacuated space between inner sphere and surrounding 45 cm inner diameter concentric sphere. For both spheres ε = 0.03 and temperature of the outer sphere is 30°C. Estimate the rate of heat flow by radiation to the oxygen in the container.

Answer 1

Given : T₁ = – 182 + 273 = 91 K, 

T₂ = 30 + 273 = 303 K, ε₁ = ε₂ = 0.03 

d₁ = 30 cm = 0.3 m, 

d₂ = 45 cm = 0.45 m. 

Rate of heat flow, Q₁₂ : 

The heat flow between the two concentric spheres by radiation is given by

For concentric spheres 

F_1-2  = 1

Now substituting the values in the above equation, we get

– ve sign shows heat flows from outside to inside.