Question

The tall tower in Melbourne Central use to hold a lead shot manufacturing facility. Molten lead droplets were poured from the top of the tower and fell into a catch bucket which was full of water at 100°C. They cooled within the bucket before coming to rest at the bottom.

(a) The lead has an initial temperature of 320°C as it enters the water. You may assume the material properties given below are constant with temperature. Calculate the time for the centre temperature to reach 110°C.

(b) For a single sphere of lead, what is the fraction of the thermal energy of the lead that is lost during the cooling process?

Data: diameter = 1.25 mm

Surface Area of a sphere = 4?r 2

h = 4,500 W/(m2 ·°C)

Volume of a sphere = 3 /4 ? r3

kwater = 0.63 W/(m·°C)

Cp,water = 4.21 kJ/(kg·°C)

klead = 16.3 W/(m·°C)

Cp,lead = 0.159 kJ/(kg·°C)

? = 10,500 kg/m3

Answer 1