Question

A flat and wide sheet material (cp = 283 J/kg K, P = 3700 kg/m", a = 6.76 x 10 m/s) of thickness 20 mm is initially uniformly heated to 1600 °C. It is then hardened by quenching it in an oil bath that is maintained at 35 °C. The convection coefficient for the oil is 460 W/m2K. Quenching is to occur for 50 seconds. Determine the Blot number used in the Hiesler charts. This may or may not be the same at that calculated above. Determine the midplane temperature of the sheets at the end of the quenching period. Answer in Determine the sheet surface temperature at the end of the quenching period. Answer in °C.

Answer 1

(a) There and conductivity , K = Pca. K= 3700x 283 x 676x10-6 k = .7.078 W ble Biot numba, Biz hec he Bi = 4.60X 20 X1003 L . 2x7.078 Bi= 0.649 from beiska charts, 676 v10 x 50 (20x103)² fo= ZZ = 0.845. 7:078 hL 460x 20 x 153 - - 0.769

midplone at temperature 0.845 .. Fo= 0 769. & I = 0.769. To-To T7 - Tribe 0.52 = 0.52 To-35 . 1600-35 To = 848.8 °C. (c) shack surface at mali temperature, : 6969 T - 35 = 0.6 846.8-35 T72. 523.28 Ć