Question

The liquid oxygen having the boiling point temperature of -183°C is to be stored in spherical container of 30cm diameter. The system is insulated by an evacuated space between the inner sphere and surrounding 45cm in diameter concentric sphere. For the outer surface of inner sphere and inner surface of outer sphere the emmisssivity is 0.03 and temperature of inner surface of outer sphere is 30°C. Neglecting the thickness of inner and outer spheres.

The rate of flow of heat by radiation to oxygen in the container

• A. 2.81 W
• B. 47.7 W
• C. 134.15 W
• D. 2.81 kW

Answer 1

The correct option is A 2.81 W


$Q_{2-1}=\frac{\sigma A_1(T_2^4-T_1^4)}{\frac{1}{{\epsilon }_1}+\frac{A_1}{A_2}(\frac{1}{{\epsilon }_2}-1)}$

$=\frac{5.67\times {10}^{-8}\times 4\pi \left(0.15{)}^2\right({303}^4-{90}^4)}{\frac{1}{0.03}+\frac{4\pi (0.15{)}^2}{4\pi (0.255{)}^2}(\frac{1}{0.03}-1)}$

$=2.81W\text{[Heat transfer from (2) to (1) ]}$