A resting adult of average size converts chemical energyin food into internal energy at

Chapter 20, Problem 70

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A resting adult of average size converts chemical energyin food into internal energy at the rate 120 W, calledher basal metabolic rate. To stay at constant temperature,the body must put out energy at the same rate. Severalprocesses exhaust energy from your body. Usually, themost important is thermal conduction into the air incontact with your exposed skin. If you are not wearinga hat, a convection current of warm air rises verticallyfrom your head like a plume from a smokestack.Your body also loses energy by electromagnetic radiation,by your exhaling warm air, and by evaporation ofperspiration. In this problem, consider still anotherpathway for energy loss: moisture in exhaled breath.Suppose you breathe out 22.0 breaths per minute, eachwith a volume of 0.600 L. Assume you inhale dry airand exhale air at 37.0C containing water vapor with avapor pressure of 3.20 kPa. The vapor came from evaporationof liquid water in your body. Model the watervapor as an ideal gas. Assume its latent heat of evaporationat 37.0C is the same as its heat of vaporization at100C. Calculate the rate at which you lose energy byexhaling humid air.