Consider a 1000-W iron whose base plate is made of 0.5-cm-thick’ aluminum alloy 20211-T6 (...

Consider a 1000-W iron whose base plate is made of 0.5-cm-thick’ aluminum alloy 20211-T6 (ρ= 2770 kg/m3, tρ= 875 J/kg · °C, α = 7.3 × 10–5 m2/s). The base plate has a surface area of 0.03 m2. Initially, the iron is in thermal equilibrium with the ambient air at 22°C. Taking the heat transfer coefficient at the surface of the base plate to be 12 W/m2 · °C and assuming 85 percent of the heat generated in the resistance wires is transferred to the plate, determine how long it will take for the plate temperature to reach 140°C. Is it realistic to assume the plate temperature to be uniform at all times?

FIGURE P18-22