We often cut a watermelon in half and put it into the freezer to cool it quickly. But usually we forget to check on it and end up having a watermelon with a frozen layer on the top. To avoid this potential problem a person wants to set the timer such that it will go off when the temperature of the exposed surface of the watermelon drops to 3°C. Consider a 25-cm-diameter spherical watermelon that is cut into two equal parts and put into a freezer at 212°C. Initially, the entire watermelon is at a uniform temperature of 25°C, and the heat transfer coefficient on the surfaces is 22 W/m2·K. Assuming the watermelon to have the properties of water, determine how long it will take for the center of the exposed cut surfaces of the watermelon to drop to 3°C. Answer: 46.7 min
We often cut a watermelon in half and put it into the freezer to cool it quickly. But
usually we forget to check on it and end up having a watermelon with a frozen layer
on the top. To avoid this potential problem a person wants to set the timer such that
it will go off when the temperature of the exposed surface of the watermelon drops
to 3°C. Consider a 25-cm-diameter spherical watermelon that is cut into two equal
parts and put into a freezer at 212°C. Initially, the entire watermelon is at a uniform
temperature of 25°C, and the
Assuming the watermelon to have the properties of water, determine how long it
will take for the center of the exposed cut surfaces of the watermelon to drop to 3°C.
Answer: 46.7 min
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