Question

An iron sphere has a radius of 0.85 meters and its surface temperature is 370 K. It is surrounded by air whose temperature is 300 K. The emissivity of iron and air is 0.985.

a. Find the heat flux that is emitted by radiation from the iron sphere.

b. Find the net flow of heat from the iron sphere.

Answer 1

Rate of heat flow from iron sphere

Therefore, heat flux is given by

  

Where, A = area of the sphere = 4r2 = (4*3.14*0.852) = 9.0746 m2

T = change in temperature = (370-300) K. = 70 K

= Steafan's constant = 5.67*10-8 W/m2K4

= emmisivity = 0.985

(a) Heat flux = (0.985*5.67*10-8*70) W/m2

= 390.95*10-8 W/m2

(b) Net heat flow = Heat flux *Area

= (390.95*10-8*9.0746) J/s

= 3547.71*10-8 J/s