Steel is sequentially heated and cooled (annealed) to relieve stresses and to make it less brittle.Consider a 100-mm-thick plate (k = 45 W/m-K, p = 7800 kg/m³, cp = 500 J/kg-K) that is initially at a uniform temperature of 300 °C and is heated (on both sides) in a gas-fired furnace for which To =700 °℃ and h = 500 W/m²-K. How long will it take for a minimum temperature of 550 °C to be reached in the plate? Neglect radiation.

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