Consider a 30-cm-diameter spherical watermelon that is cut into two equal parts and put into a freezer at -12oC. Initially the entire watermelon is at a uniform temperature of 25oC and the heat transfer coefficient on the surface is 30 W/m2oC. To avoid frosting of the watermelon surface, it is desired to take watermelon out of the freezer once its surface temperature reaches 3oC. Assuming the watermelon to have the properties of water, how long it will take for the centre of the exposed cut surface to drop to 3oC. Note: for water k = 0.607 W/moC, and α = 0.146×10-6 m2/s.