posted on 2012-01-20, 12:08authored byPeter Broede, George HavenithGeorge Havenith, Xiaoxin Wang, Victor Candas, Emiel A. den Hartog, Barbara Griefahn, Ingvar Holmer, Kalev Kuklane, Harriet Meinander, Wolfgang Nocker, Mark Richards
In order to assess the non-evaporative components of the reduced thermal insulation of wet
clothing, experiments were performed with a manikin and with human subjects in which two
layers of underwear separated by an impermeable barrier were worn under an impermeable
overgarment at 20 °C, 80% RH and 0.5 ms-1 air velocity. By comparing manikin measurements
with dry and wetted mid underwear layer, the increase in heat loss caused by a wet layer kept away
from the skin was determined, which turned out to be small (5-6 Wm-2), irrespective of the inner
underwear layer being dry or wetted, and was only one third of the evaporative heat loss calculated
from weight change, i.e. evaporative cooling efficiency was far below unity.
In the experiments with 8 males, each subject participated in two sessions with the mid underwear
layer either dry or wetted, where they stood still for the first 30 minutes and then performed
treadmill work for 60 minutes. Reduced heat strain due to lower insulation with the wetted mid
layer was observed with decreased microclimate and skin temperatures, lowered sweat loss and
cardiac strain. Accordingly, total clothing insulation calculated over the walking period from heat
balance equations was reduced by 0.02 m2 °C W-1 (16%), while for the standing period the same
decrease in insulation, representing 9% reduction only showed up after allowing for the lower
evaporative cooling efficiency in the calculations. As evaporation to the environment and inside
the clothing was restricted, the observed small alterations may be attributed to the wet mid layer’s
increased conductivity, which, however, appears to be of minor importance compared to the
evaporative effects in the assessment of the thermal properties of wet clothing.
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BRODE, P....et al., 2008. Non-evaporative effects of a wet mid layer on heat transfer through protective clothing. European Journal of Applied Physiology, 2008, 104(2), pp.341 - 349