solution

Valyrian steel is produced in 1 m long slabs with cross sections of 10 cm by 10 cm. The slabs, initially at 950 K, are cooled in air at 300 K giving a heat transfer coefficient of 200 W/m2K a. Estimate the time required for the temperature at the centre of a slab to decrease to [10] 315 K In order to improve the cooling process, the 1 m long slabs are cut into 50 cm long sections with the same initial temperature and cross sections of the slabs in part (a). They are also cooled by strong air jets at 300 K giving a heat transfer coefficient of 400 W/m2K b. Estimate the temperature at the centre of a single 50 cm-long section after 16 minutes. [15] Valyrian steel has the following properties: p-7840 kg/m3, c 460 J/kg-K, k 50 W/m-K and a-13.9 x 106 m2/s. Neglect radiation