Tham khảo tài liệu 'coatings technology handbook episode 3 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 106-2 Coatings Technology Handbook Third Edition TABLE Metabolic Rates Perspiration Production and Vapor Permeability Requirements for Various Levels of Physical Activity Activity Metabolic Fate W Water Evaporation Rate g 24 h Vapor Permeability Rate g m2 24 h Sleeping 60 600 200 Sitting 100 3800 1300 Gentle walking 200 7600 2500 Active walking 300 11 500 3800 Active walking on the level carrying a heavy pack 400 15 250 5000 Active walking in the mountains carrying a heavy pack 600-800 23 000-30 000 8000-10 000 Very heavy work 100 3800 13 000 EC heat required to expand the vapor from 34 C 100 RH to 27 C 100 RH 9 calories EV heat required to expand the air containing the evaporated water in order to reduce its relative humidity from 100 to the humidity of the ambient air 50 23 calories Hence the total cooling energy derived from evaporating 1 g of liquid perspiration and dissipating it into the surrounding atmosphere is Et 578 9 23 620 calories This is true only of course if the clothing is capable of transmitting the vapor to the ambient atmosphere without a change of phase or of temperature other than that provided for in the calculation . It is clear then that the moisture vapor permeability of the clothing must be high enough to pass vaporized perspiration at the rate at which it is being produced at the skin. Vapor Permeability Requirements Any estimate of the vapor permeability requirements of clothing must be based on estimates of a number of factors that depend on body size and physiology. Since these vary significantly from individual to individual and even for one individual from one time to another no precise values can be given. One of those factors consists of the metabolic rates corresponding to various levels of physical activity. Representative values of metabolic rates are shown in Table . Some of this metabolic energy is used to perform the work that is being done. Most of it however is turned into heat which must be dissipated. .
