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Question: a person can be modelled as a heat engine that...

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A person can be modelled as a heat engine that does work where the energy is input as food that is metabolized by the body. A person of surface area 1.3 m2 and with a radiative emissivity of 0.82 consumes a meal comprising of 1.45 MJ of energy. All of the energy is expended over a time of 1 hour by exercise (work), radiative heat loss and perspiration.

(a) What is the heat loss by perspiration if 104 mL of sweat is evaporated from the person’s skin? [Note that the latent heat of vapourization of water increases slightly for temperatures below 100°C – hence here use Lvap = 2.42 ×106 J/kg rather than the value in the notes/textbook].

(b) How much energy is radiated if the person’s external surface temperature is 36°C and the environment temperature is 22°C?

(c) How much power is the person putting into the exercise?

(d) What is the person’s efficiency as a heat engine? 

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