Overall, 80% of the energy used by the body must be eliminated as excess
thermal energy and needs to be dissipated. The mechanisms of
elimination are radiation, evaporation of sweat (2 430 𝑘𝐽/𝑘𝑔) evaporation
from the lungs (38 kJ/h), conduction, and convection. A person working
out in a gym has a metabolic rate of 2 500 kJ/h. His body temperature is
37°C, and the outside temperature 24°C. Assume the skin has an area of
2.0 m2 and emissivity of 0.97.
a) At what rate is his excess thermal energy dissipated by
radiation? (4 marks)
b) If he eliminates 0.40 kg of perspiration during that hour, at what
rate is thermal energy dissipated by evaporation of sweat?
c) At what rate is energy eliminated by evaporation from the lungs?
d) At what rate must the remaining excess energy be eliminated
through conduction and convection? (4 marks)
Overall, 80% of the energy used by the body must be eliminated as excess
thermal energy and needs to be dissipated. The mechanisms of
elimination are radiation, evaporation of sweat (2 430 𝑘𝐽/𝑘𝑔) evaporation
from the lungs (38 kJ/h), conduction, and convection. A person working
out in a gym has a metabolic rate of 2 500 kJ/h. His body temperature is
37°C, and the outside temperature 24°C. Assume the skin has an area of
2.0 m2 and emissivity of 0.97.
a) At what rate is his excess thermal energy dissipated by
radiation? (4 marks)
b) If he eliminates 0.40 kg of perspiration during that hour, at what
rate is thermal energy dissipated by evaporation of sweat?
c) At what rate is energy eliminated by evaporation from the lungs?
d) At what rate must the remaining excess energy be eliminated
through conduction and convection? (4 marks)
