Before ironing, an iron needs to be
warmed up to a certain temperature. The iron temperature is different
for different fabric. The resistance wires are used to generate the energy
warm the iron up.
The power of the iron is =
100 W and 85% of the heat generated in the resistance wires is
transferred to the iron base plate
The materials of the base plate is aluminum alloy
2024-76 (ρ = 2770 kg/m3 and
875 J/(kg-oC)) and the base plate thickness δ =
0.5 cm, and the area is A = 0.02 m2
Initially the iron is in equilibrium with the ambient air at
Tinitial = 20 oC
The convection heat transfer coefficient h = 35 W/(m2-oC)
The emissivity of the base plate to the ambient ε = 0.6
Determine the minimum time needed for the base plate
temperature to reach Tfinal = 140 oC.
After the temperature reaches
how much energy is needed to keep the base at 140 oC?
Energy Balance Diagram
The heat needed to increase the base plate's temperature
from Tinital to Tfinal is:
Q = cp m (Tfinal - Tinitial)
m = mass of the base
cp = specific heat
The energy balance of the base plate (Energy balance
will be introduced in the following section):
Energy in: 85% of the heat generated by the wires.
Energy out: convection, radiation heat loss to the ambient air.
Energy storage: the energy in the base to increase the base's temperature.