Question

2 Two spheres, A and B, both initially at 700K, are quenched in liquid baths at 300K. They have diameters 300 and 30 mm, density 1600 and 400 kg/m3, specific heat 0.4 and 1.6 kJ kg1 K1, thermal conductivities 170 and 3.4 Wm-1.K, and convection coefficients 5 and 50 Wm- 2K-1, respectively. Sketch the temperature histories of each sphere on T-t axes, calculate the time taken for the surface of each sphere to reach 400 K, and calculate the energy gained by each bath as the spheres cool to 400 K. (ans 8872 s, 88.72 s, 2.714 MJ, 2.714 kJ)

Answer 1