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 28°C. Assume the skin has an area of 2.0 m2 and emissivity of 0.97. (0 = 5.6696 x 10-8 w/m2. K4) (a) At what rate is his excess thermal energy dissipated by radiation? (Enter your answer to at least one decimal place.) (b) If he eliminates 0.41 kg of perspiration during that hour, at what rate is thermal energy dissipated by evaporation of sweat? (Enter your answer to at least one decimal place.) (c) At what rate is energy eliminated by evaporation from the lungs? (Enter your answer to at least one decimal place.) (d) At what rate must the remaining excess energy be eliminated through conduction and convection?

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 28°C. Assume the skin has an area of 2.0 m2 and emissivity of 0.97. (0 = 5.6696 x 10-8 w/m2. K4) (a) At what rate is his excess thermal energy dissipated by radiation? (Enter your answer to at least one decimal place.) (b) If he eliminates 0.41 kg of perspiration during that hour, at what rate is thermal energy dissipated by evaporation of sweat? (Enter your answer to at least one decimal place.) (c) At what rate is energy eliminated by evaporation from the lungs? (Enter your answer to at least one decimal place.) (d) At what rate must the remaining excess energy be eliminated through conduction and convection?

Physics for Scientists and Engineers: Foundations and Connections

1st Edition

ISBN:9781133939146

Author:Katz, Debora M.

Publisher:Katz, Debora M.

Chapter21: Heat And The First Law Of Thermodynamics

Section: Chapter Questions

Problem 71PQ

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