Chapter 4 Transient Heat Conduction4-20An iron whose base plate is made of an aluminum alloy is turned on. The time for the plate temperature to reach 140°C and whether it is realistic to assume the plate temperature to be uniform at all times are to be determined. Assumptions185 percent of the heat generated in the resistance wires is transferred to the plate. 2The thermal properties of the plate are constant. 3The heat transfer coefficient is constant and uniform over the entire surface. PropertiesThe density, specific heat, and thermal diffusivity of the aluminum alloy plate are given to be ρ= 2770 kg/m3, Cp= 875 kJ/kg.°C, and α= 7.3×10-5m2/s. The thermal conductivity of the plate can be determined from α= k/(ρCp)= 177 W/m.°C (or it can be read from Table A-3). AnalysisThe mass of the iron's base plate is Air 22°CIRON 1000 W mVLA====ρρ()(.)(.).27700 0050 030 4155kg / mmmkg32Noting that only 85 percent of the heat generated is transferred to the
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