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Evaporative Cooling: effective latent heat of evaporation in relation to evaporation distance from the skin

Havenith, George; Bröde, Peter; Emiel, den Hartog; Kuklane, Kalev LU ; Holmér, Ingvar LU ; Rossi, Rene M; Richards, Mark; Farnworth, Brian and Wang, Xiaoxin (2013) In Journal of Applied Physiology 114(6). p.778-785
Abstract
Calculation of evaporative heat loss is essential to heat balance calculations. Despite recognition that the value for latent heat of evaporation, used in these calculations, may not always reflect the real cooling benefit to the body, only limited quantitative data on this is available which has found little use in recent literature. In this experiment a thermal manikin (MTNW, Seattle) was used to determine the effective cooling power of moisture evaporation. The manikin measures both heat loss and mass loss independently allowing a direct calculation of an effective latent heat of evaporation (λeff). The location of the evaporation was varied: from the skin or from the underwear or from the outerwear. Outerwear of different... (More)
Calculation of evaporative heat loss is essential to heat balance calculations. Despite recognition that the value for latent heat of evaporation, used in these calculations, may not always reflect the real cooling benefit to the body, only limited quantitative data on this is available which has found little use in recent literature. In this experiment a thermal manikin (MTNW, Seattle) was used to determine the effective cooling power of moisture evaporation. The manikin measures both heat loss and mass loss independently allowing a direct calculation of an effective latent heat of evaporation (λeff). The location of the evaporation was varied: from the skin or from the underwear or from the outerwear. Outerwear of different permeabilities was used and different numbers of layers were used. Tests took place in 20ºC, 0.5 m.s-1 at different humidities and were performed both dry and with a wet layer allowing the breakdown of heat loss in dry and evaporative components.

For evaporation from the skin λeff is close to the theoretical value (2430J.g-1), but starts to drop when more clothing is worn, e.g. by 11% for underwear and permeable coverall. When evaporation is from the underwear, λeff reduction is 28% wearing a permeable outer. When evaporation is from the outermost layer only, the reduction exceeds 62% (no base-layer) increasing towards 80% with more layers between skin and wet outerwear. In semi- and impermeable outerwear the added effect of condensation in the clothing opposes this effect. A general formula for the calculation of λeff was developed. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
sweat Latent heat of evaporation evaporative cooling efficiency protective clothing wicking indirect calorimetry
in
Journal of Applied Physiology
volume
114
issue
6
pages
778 - 785
publisher
American Physiological Society
external identifiers
  • wos:000316206100010
  • scopus:84878582168
ISSN
1522-1601
DOI
10.1152/japplphysiol.01271.2012.
project
EU project “THERMPROTECT, Assessment of Thermal Properties of Protective Clothing and Their Use”, contract G6RD-CT-2002-00846
language
English
LU publication?
yes
id
75e29161-b894-4906-a0bc-5e4ba1b8d0a8 (old id 3362913)
date added to LUP
2014-03-14 15:25:21
date last changed
2019-08-18 03:09:31
@article{75e29161-b894-4906-a0bc-5e4ba1b8d0a8,
  abstract     = {Calculation of evaporative heat loss is essential to heat balance calculations. Despite recognition that the value for latent heat of evaporation, used in these calculations, may not always reflect the real cooling benefit to the body, only limited quantitative data on this is available which has found little use in recent literature. In this experiment a thermal manikin (MTNW, Seattle) was used to determine the effective cooling power of moisture evaporation. The manikin measures both heat loss and mass loss independently allowing a direct calculation of an effective latent heat of evaporation (λeff). The location of the evaporation was varied: from the skin or from the underwear or from the outerwear. Outerwear of different permeabilities was used and different numbers of layers were used. Tests took place in 20ºC, 0.5 m.s-1 at different humidities and were performed both dry and with a wet layer allowing the breakdown of heat loss in dry and evaporative components. <br/><br>
For evaporation from the skin λeff is close to the theoretical value (2430J.g-1), but starts to drop when more clothing is worn, e.g. by 11% for underwear and permeable coverall. When evaporation is from the underwear, λeff reduction is 28% wearing a permeable outer. When evaporation is from the outermost layer only, the reduction exceeds 62% (no base-layer) increasing towards 80% with more layers between skin and wet outerwear. In semi- and impermeable outerwear the added effect of condensation in the clothing opposes this effect. A general formula for the calculation of λeff was developed.},
  author       = {Havenith, George and Bröde, Peter and Emiel, den Hartog and Kuklane, Kalev and Holmér, Ingvar and Rossi, Rene M and Richards, Mark and Farnworth, Brian and Wang, Xiaoxin},
  issn         = {1522-1601},
  keyword      = {sweat Latent heat of evaporation evaporative cooling efficiency protective clothing wicking indirect calorimetry},
  language     = {eng},
  number       = {6},
  pages        = {778--785},
  publisher    = {American Physiological Society},
  series       = {Journal of Applied Physiology},
  title        = {Evaporative Cooling: effective latent heat of evaporation in relation to evaporation distance from the skin},
  url          = {http://dx.doi.org/10.1152/japplphysiol.01271.2012.},
  volume       = {114},
  year         = {2013},
}