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

Research output: Contribution to journalArticle

Abstract

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.

Details

Authors
  • George Havenith
  • Mark Richards
  • Xiaoxin Wang
  • Peter Bröde
  • Victor Candas
  • Emiel den Hartog
  • Ingvar Holmér
  • Kalev Kuklane
  • Harriet Meinander
  • Wolfgang Nocker
Organisations
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Physiology

Keywords

  • heat balance, evaporative cooling efficiency, condensation, sweat evaporation, protective clothing
Original languageEnglish
Pages (from-to)142-149
JournalJournal of Applied Physiology
Volume104
Issue number1
Publication statusPublished - 2008
Publication categoryResearch
Peer-reviewedYes