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

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 75 g/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.