The production line of a special biscuit at 30 ̊C and 1 atm has a 0.8 X 0.8 (m) square plate. One side of the plate is maintained at a temperature of 100 ̊C, while the other side is insulated....

The production line of a special biscuit at 30 ̊C and 1 atm has a 0.8 X 0.8 (m)

square plate. One side of the plate is maintained at a temperature of 100 ̊C,

while the other side is insulated.

 Determine the rate of heat transfer from the plate by natural convection if the

plate

(i) Is horizontal with the hot surface facing down;

(ii) Is horizontal with the hot surface facing up;

Data: The properties of air at the film temperature are: thermal conductivity, k=

0.0279 W/m.k); kinematic viscosity= 1.815 x 10-5 m2/s; Pr = 0.709