Consider a 0.6-m 0.6-m thin square plate in a room at 30°C. One side of the
plate is maintained at a temperature of 90°C, while the other side is insulated,
as shown in Figure 9–15. Determine the rate of heat transfer from the plate by
natural convection if the plate is (a) vertical, (b) horizontal with hot surface facing
up, and (c) horizontal with hot surface facing down.