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Apparent latent heat of evaporation from clothing: attenuation and “heat pipe” effects

På svenska

Author

  • George Havenith
  • Mark Richards
  • Xiaoxin Wang
  • Peter Bröde
  • Victor Candas
  • Emiel den Hartog
  • Ingvar Holmér
  • Kalev Kuklane
  • Harriet Meinander
  • Wolfgang Nocker

Summary, in English

Investigating claims that a clothed person’s mass loss does not always represent their evaporative heat loss (EVAP), a thermal manikin study was performed measuring heat balance components in more detail than human studies would permit. Using clothing with different levels of vapor permeability and measuring heat losses from skin controlled at 34°C in ambient temperatures of 10, 20, and 34°C with constant vapor pressure (1 kPa), additional heat losses from wet skin compared with dry skin were analyzed. EVAP based on mass loss (Emass) measurement and direct measurement of the extra heat loss by the manikin due to wet skin (Eapp) were compared. A clear discrepancy was observed. Emass overestimated Eapp in warm environments, and both under and overestimations were observed in cool environments, depending on the clothing vapor permeability. At 34°C, apparent latent heat ((lambda)app) of pure evaporative cooling was lower than the physical value ((lambda); 2,430 J/g) and reduced with increasing vapor resistance up to 45%. At lower temperatures, (lambda)app increases due to additional skin heat loss via evaporation of moisture that condenses inside the clothing, analogous to a heat pipe. For impermeable clothing, (lambda)app even exceeds (lambda) by four times that value at 10°C. These findings demonstrate that the traditional way of calculating evaporative heat loss of a clothed person can lead to substantial errors, especially for clothing with low permeability, which can be positive or negative, depending on the climate and clothing type. The model presented explains human subject data on EVAP that previously seemed contradictive.

Publishing year

2008

Language

English

Pages

142-149

Publication/Series

Journal of Applied Physiology

Volume

104

Issue

1

Document type

Journal article

Publisher

American Physiological Society

Topic

  • Physiology

Keywords

  • heat balance
  • evaporative cooling efficiency
  • condensation
  • sweat evaporation
  • protective clothing

Status

Published

Project

  • EU project “THERMPROTECT, Assessment of Thermal Properties of Protective Clothing and Their Use”, contract G6RD-CT-2002-00846

Research group

  • Thermal Environment Laboratory

ISBN/ISSN/Other

  • ISSN: 1522-1601