Apples of diameter 12 cm are picked from a tree and cooled in a stream of cold water to reduce its metabolism so that it stores longer. Consider a stream of water at 5 degC and a velocity of 0.04 m/s flowing over an individual apple. If the initial uniform temperature of the apple was 25 degC, calculate the time it takes for the center of the apple to reach 8 degC.
Hint: Calculate Biot number to confirm that both external convection and internal conduction are important in this problem.