A 1000-W iron is left on an ironing board with its base exposed to the air at 20°C. The convection heat transfer coefficient between the base surface and the surrounding air is 35?W/m2•K. If the base has an emissivity of 0.6 and a surface area of 0.02 m2, determine the temperature of the base of the iron.
What will be an ideal response?
A 1000-W iron is left on the iron board with its base exposed to the air at 20°C. The temperature of the base of the iron is to be determined in steady operation.
Assumptions 1 Steady operating conditions exist. 2 The thermal properties of the iron base and the convection heat transfer coefficient are constant and uniform. 3 The temperature of the surrounding surfaces is the same as the temperature of the surrounding air.
Properties The emissivity of the base surface is given to be ? = 0.6.
Analysis At steady conditions, the 1000 W energy supplied to the iron will be dissipated to the surroundings by convection and radiation heat transfer. Therefore,
where
and
Substituting,
Solving by trial and error gives
Discussion We note that the iron will dissipate all the energy it receives by convection and radiation when its surface temperature reaches 947 K.
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