consider a 0.6-m 0.6-m thin square plate in a room at 30c. one side of the plate is maintained at a temperature of 90c, while the other side is insulated, as shown in fig. 9-18. determine the rate of heat transfer from the plate by natural convection if the plate is (a)vertcal, (b) horizontal with hot surface facing up, and (c) horizontal with hot surface facing down.