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Cooling and heat transfer of/from various materials.

An imaginary dimensionless room has a ceiling fan that moves 10 cubic feet of air per minute. Assuming the air flow is directed downward at a temperature of 65 degrees F --- there are 3 materials below at which the ceiling fan air is directed:

1) A 1 gallon container of water at 140 degrees F
2) A 1 pound block of wood at 220 degrees F
3) And a piece of bread/toast weighing 0.1 lbs at 150 degrees F

Calculate the amount of time needed to cool each of the 3 materials above to 65 degrees F?

Please show the calculations as to how to arrive at the desired answers!

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Solution Preview

Assumption: Continuous flow of air is constant in temperature.

First we calculate the amount of energy required to cool each material to 65F (18C) using the equation Q=mcdeltaT:
1. Water at 140F or 60C.
Specific heat of water = 4.18 kJ/kgC
Qwater=mcdeltaT = 3.78*4.18*(60-18) = 663.6 (kJ)

2. 1 pound of block of wood at 220F ...

Solution Summary

The time required to lower the temperature of three objects with a fan is calculated.