Apparent evaporative cooling efficiency in clothing with continuous perspiration: A sweating manikin study

Abstract

Apparent evaporative cooling efficiency has typically been determined by applying a pre-wetted fabric "skin" on a dummy ("manikin") simulating human thermal physiology, to understand the effective cooling components of body perspiration in clothing systems. This procedure is only a very rough approximation of real life, as the pre-wetted fabric does not have the capacity to continuously push extra moisture into the clothing layers, which would happen with continuous sweating of the body. In this study, a sweating torso was used to mimic different sweating situations (100, 175 and 250 g/h) with twelve single-layer (SI) and multilayer (MU) clothing systems to understand the effect of continuous sweating and its interaction with clothing materials on cooling efficiency. Our experiments revealed that evaporative cooling efficiency is affected differently by continuous sweating when compared to pre-wetted fabric "skin" approaches. With continuous sweating, up to 15 % (24 W•m -2 ) cooling power came from the so-called "heat pipe effect" and/or wet conduction and 24 % (44 W•m -2 ) evaporative latent heat was gained from the environment. It was found that the increase of perspired moisture can affect evaporative cooling efficiency for hydrophilic materials in dual ways. For each 75g/h sweat rate increase, the in-plane moisture transfer can raise the evaporative cooling efficiency of SIs at least 3-12 % and the transplanar moisture transfer may reduce the evaporative cooling efficiency by at least 2-7 % and 2-9 % for SIs and MUs, respectively. For hydrophobic materials, the evaporative cooling efficiency was less affected by different levels of perspiration due to low wicking. Results also showed the negative correlation of evaporative cooling efficiency of hydrophilic materials with fabric evaporative resistance and thickness. Our study contributes to the understanding of the effective sweat cooling power and evaporative latent heat from environment for the clothed human body with continuous sweating. It also provides insight into the interaction between liquid and water vapor transport, and material design for optimizing the evaporative cooling.

Moisture transfer of the clothing–human body system during continuous sweating under radiant heat

“…1, all the sweat may evaporate on the skin; if cooling 5 1, there may be sweat evaporating from the clothing layer.) (I) As shown in a previous study, 51 4 out of 15 hydrophilic SU cases (five SUs at three sweat rates) with cooling lower than 1 (p < 0.05), which demonstrates that part of the sweat possibly evaporated from the clothing material. Meanwhile, _ m accu was zero for these cases.…”

“…Through combined analyses of the transfer rates and the apparent evaporative cooling efficiency ( ) 3 25 , we can also get indications about the dynamic moisture transfer process. (I) As shown in a previous study 51 , four out of fifteen hydrophilic SU cases (five SUs at three sweat rates) with lower than 1 (p < 0.05) demonstrates that part of the sweat possibly evaporated from the clothing material. Meantime, ̇ was zero for these cases.…”

Evaporative Mist Cooling as Heat Dissipation Technique: Experimental Assessment and Modelling

“…Droplet temperature can then be applied to define the efficiency of energy exchange at any given time. Energy exchange efficiency constitutes a very significant indicator of the performance of different cooling technologies in general and has been used as such [46], as well as for evaporative cooling [47,48]. Energy exchange efficiency in evaporative cooling is defined as the ratio between the actual variation in temperature in the droplet due to the cooling system and the maximum variation possible, i.e., to reach wet bulb temperature.…”

Prediction of the water evaporation rate of wet textile materials in a pre-defined environment

“…Moreover, for female exercisers, they often experience breast discomfort and muggy because of the additional multi-layer of sports bras (Bartels, 2005;Krenzer et al, 2005). Evaporation moved from close to the skin surface to the outer surface of the clothing will lower the potential for skin cooling by this means because part of the heat required for evaporation will be taken from the ambient air (Nielsen and Endrusick, 1992;Guan et al, 2019). If there is an air gap between skin and clothing, "heat pipe" effect might be present (Havenith et al, 2008).…”