7. Someone is walking outside when the temperature of the air is -10°C. The meta

Question

7. Someone is walking outside when the temperature of the air is -10°C. The metabolic rate of walking is 140 Cal/m2hr, and the usual muscle efficiency (20%) applies. They are completely covered by clothing with a coefficient of thermal conductivity of 0.36 Cal-cm/m2 hr °C. Their total surface area is 1.7 m2, and this area can be used as the area through which heat is being conducted away from the body. Their skin temperature is the same as the inside surface of the clothing, 35°C. The temperature of the outside of the clothing is -10°C. It is dark outside. Their mass is 75 kg. Ignore heat lost to breathing. How thick does the down have to be to maintain a constant internal body temperature of 37°C?

Explanation / Answer

the rate at which the persons heat is maintained by the metabolic work is 140cal*1.7*1hr*20/100=47.6cal this is the ha=eat produced in 1 hr 1.7 because surface area of the body, 20/100 because the muscles are only 20 percent efficient the rate at which he is loosing heat to the environment assuming the clothing is of thickness x. T/[kA/x]=47/[0.36*1.7/x] x in cms and this is heat loss per hour x=0.6198cms

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