Human lung capacity varies from about 4 L to 6 L, so we shall use an average of

Question

Human lung capacity varies from about 4 L to 6 L, so we shall use an average of 5.0 L. The air enters at the ambient temperature of the atmosphere and must be heated to internal body temperature at an approximately constant pressure of 1.0 atm in our model. Suppose you are outside on a winter day when the temperature is -15 F.

How much heat must your body have supplied to get the 5.0 L of air up to internal body temperature, assuming that the atmosphere is all N2? Express your answer in joules to three significant figures.

Explanation / Answer

Volumetric capacity of air (Va) = 0.001297 J/cc K.

Human body temperature in Kelvin = 310.15 K

Outside environment temperature = -15F = 247.04 K

Heat supplied by the body E = Va × Inhaled air in lungs × change in temp

E = 0.001297 J/cc K × 5 L × (1000 cc / 1L) × (310.15 K - 247.04K)

E = 409.27J

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