White potatoes (k=0.60 W/m,C and a =0.20 x 10-6 m2/s) in spherical shape that are initially at a uniform temperature of 30 C and have an average diameter of 5 cm are to be cooled by refrigerated air at 4 C flowing at a velocity of 5 m/s. The average heat transfer coefficient between the potatoes and the air is experimentally determined to be 25 W/m2.C. Determine how long it will take for the center temperature of the potatoes to drop to 4 C. Also, determine the surface temperature of the potato. (Use Heisler Charts.)