The surfaces of two concentric spheres having radii of 75 and 100 mm are maintained at 325 K and 275 K, respectively.
(a) If the space between the spheres is filled with nitrogen at 5 atm, estimate the convection heat transfer rate.
(b) If both sphere surfaces are black, estimate the total rate of heat transfer between them.
(c) Suggest ways to reduce the heat transfer.
GIVEN
Concentric spheres with nitrogen between them
Nitrogen pressure (p) = 5 atm
Sphere radii
Inner sphere (ri) = 75 mm = 0.075 m
Outer sphere (ro) = 100 mm = 0.1 m
Sphere temperatures
Inner sphere (Ti) = 325 K
Outer sphere (To) = 275 K
Both spheres are black
ASSUMPTIONS
Sphere temperatures are constant and uniform
Only the density of the nitrogen is affected significantly by pressure
The nitrogen behaves as an ideal gas