Consider a thin 16-cm-long and 20-cm-wide horizontal
plate suspended in air at 208C. The plate is equipped with
electric resistance heating elements with a rating of 20 W.
Now the heater is turned on and the plate temperature rises.
Determine the temperature of the plate when steady operating
conditions are reached. The plate has an emissivity of
0.90 and the surrounding surfaces are at 178C. As an initial
guess, assume a surface temperature of 508C. Is this a good
assumption?