The temperature controller for a clothes dryer consists of a biometallic switch mounted on an electrical heater attached to a wall - mounted insulation pad.
The switch is set to open at 70°C, the maximum dryer air temperature. In order to operate the dryer at a lower air temperature, sufficient power is supplied to the heater such that the switch reaches 70 °C (Tset) when the air temperature T is less than Tset .If the convection heat transfer coefficient between the air and the exposed switch surface of 30 mm2 is 25 W/m2 .K, how much heater power Peis required when the desired dryer air temperature is T8 = 50°C?