Effects of condensation in clothing on heat transfer

Abstract

A condensation theory is presented that enables the calculation of the rate of vapour transfer with its associated effects on temperature and total heat transfer inside a clothing ensemble consisting of underclothing, enclosed air, and outer garment. The model is experimentally tested by three experiments: (1) impermeable garments worn by subjects with and without plastic wrap around the skin, blocking sweat evaporation underneath the clothing; (2) comparison of heat loss in impermeable and semi-permeable garments and the associated discomfort and strain; (3) subjects working in impermeable garments in cool and warm environments at two work rates, until tolerance. The measured heat exchange and temperatures are calculated with satisfying accuracy by the model (mean error = 11, SD = 10 Wm-2 for heat flows and 0.3 and 0.9 degree C for temperatures, respectively). A numerical analysis shows that for total heat loss the major determinants are vapour permeability of the outer garment, skin vapour concentration and air temperature. In the cold the condensation mechanism may completely compensate for the lack of permeability of the clothing as far as heat dissipation is concerned, but in the heat impermeable clothing is more stressful.

A simple theoretical model of heat and moisture transport in multi-layer garments in cool ambient air

“…The analysis presented in this paper, together with similar analyses published previously by Lotens, et al (1995) and by Fukazawa, et al (2003a), establish a rational basis for analyzing heat and water vapour transport with condensation in a cool garment. In the simplest condition, moisture condenses on the cool inner surface of an impervious outer garment, where latent heat carried by water vapour is converted to sensible heat which is transferred by conduction, convection, and radiation to the environment.…”

“…In principle, our analysis is similar to that of Lotens, et al (1995) who showed that concepts presented in this paper are sufficient to account for heat loss from exercising subjects wearing either semi-permeable or impermeable garments in a cool environment. In practice, however, our analysis is different from that of Lotens, et al in that we were able to demonstrate good agreement between computed and measured values of sensible and evaporative heat loss for several well defined systems, while Lotens, et al used data for exercising subjects to validate their analysis.…”

“…However, we were able to develop an iterative numerical analysis that did yield temperatures, partial pressures of water, and vapour flow rates consistent with experimental observations. The numerical analysis was based on four criteria that were completely consistent with the physical principles stated by Lotens, et al (1995). The only difference was that the numerical method permits condensation at several different locations within the garment, which definitely occurred in the system studied by Yoo and Kim (2008).…”

“…The purposes of the present paper are: (1) to demonstrate that the method developed by Lotens, et al (1995) provides a rational explanation for the results observed by Havenith, et al (2008), and (2) to extend applicability of the method to systems other than those considered by Lotens, et al and Fukazawa, et al We compare heat transfer rates computed using clothing properties derived from flat-plate data with heat transfer rates measured on a clothed manikin. Although manikin data involve fewer extraneous factors than data generated with exercising human subjects, uneven distribution of air between the inner and outer garments still presents a significant problem.…”

“…The principal difference between our approach and the approaches employed by Lotens, et al (1995) and Fukazawa, et al (2003b) is that neither of those authors considered the effect of an air space separating inner and outer garments, and they assumed a priori that condensation occurs at a particular location within the garment. Lotens, et al assumed that condensation occurs at the inner garment-outer garment interface when the outer garment permeability for water vapour is much lower than the permeability of the inner garment.…”