Problem 3. Consider two black coaxial parallel circular disks of equal diameter D that are spaced apart by a distance L. The top and bottom disks have uniform temperatures of 500° C and 520°C, respectively. Determine the radiation heat transfer coefficient hrad between the disks if they are spaced apart by L = D. A₂ D T2=500°C T₁ = 520°C

Fig: 1