4. (20 pts) You are in charge of an industrial donut hole production process.The donut holes are cooked in a preheated convection oven at 200 °C, andthey are considered fully

cooked when the temperature at the centerreaches 150 °C. The donut holes have a diameter of 2.5 cm, which you mayassume to be constant during the baking process. The average specificheat of the dough is 1.15 kJ/kgK, its average conductivity is 0.084 W/mK,and its average density is 0.98 g/cm (in reality these quantities changeduring baking, but you may assume they are constant). The effective heattransfer coefficient between the donut holes and the air in the oven is12 W/m K. You may ignore heating by radiation from the oven walls.

Fig: 1