A copper sheet (k = 400 W/m·K, rho = 8900 kg/m3 , c = 380 J/kg·K) of thickness 2L = 4 mm has an initial temperature of 118◦C. It is suddenly quenched in liquid water. (a) It is assumed that the convection coefficient is 1200 W/m2 ·K. If the water temperature is 100◦C, find the time required for the sheet to reach a temperature of 104◦C. (b) To find a more accurate solution, we can account for the boiling of water at the sheet’s two surfaces. Newton’s law of cooling is now expressed as q 00 = h(Ts − Tsat) where the saturation temperature of water is Tsat = 100◦C and the variable convection coefficient is h = 200(Ts − Tsat) 2 W/m2 ·K. Using the lumped cap