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6. White potatoes (k = 0.50 W/m °C and a = 0.13 * 10-6 m²/s) that are initially at a uniform

temperature of 25 °C and have an average diameter of 6 cm are to be cooled by

refrigerated air at 2 °C flowing at a velocity of 4 m/s. The average heat transfer coefficient

between the potatoes and the air is experimentally determined to be 19 W/m² °C.

a. Determine how long it will take for the center temperature of the potatoes to drop

to 6 °C. (25 pts)

b. Determine if any part of the potatoes will experience chilling injury (drop below 3

°C) during this process. (5 pts)

k

Bi hr

0.877

Air

2°C

4 m/s

T(r)-T

To-To

Spring 2023

Potato

T₁ = 25°C

0.6 (Fig. 4-15b)

%0

which gives surface=T +0.6(T₂-T₂)=2+0.6(6-2)=4.4°C

The slight difference between the two results is due to the reading error of the charts.

Fig: 1