On Heat and Moisture Transfer in Body-clothing System, and, Feasibility of Perspiration Based Infrared Camouflage

Making clothed human body invisible to various thermal infrared cameras has been the interest of researchers for many years. Current technologies used to accomplish the infrared camouflage all rely on external or additional resources, ignoring that our human body actually has its own heat dissipation capability, applicable to and sufficient for the purpose. That is, besides sensible heat release by the mechanisms of conduction, convection and radiation, our body has a very powerful path to dissipate heat by latent thermal release: sweat evaporation. So if, a clothing system can be designed to have the sufficient function of restraining the sensible heat release while encouraging the latent heat release via sweat evaporation, it may discharge the body heat, and lower the cloth surface temperature so as to suppress the infrared detectability.;Based on this idea, a new scheme of perspiration based infrared camouflage and the corresponding multi-layer cloth prototype were proposed in this study. A steady-state model was first developed to theoretically verify its feasibility, and the influences of each structural parameter on the effect of infrared camouflage were also discussed. Then, several experiments were conducted on a layered structure, not ideal but similar to the proposed cloth prototype, and the original theories were modified to suit the experimental system. The experimental results compared well with the theoretical predictions in verifying the principle of proposed perspiration based infrared camouflage, and in examining the effects of such factors as layer thickness and layer sequence. Furthermore, in place of the one-dimensional steady-state model assuming the transfer process along the direction of cloth thickness only, a more comprehensive theoretical treatment of coupled heat and moisture transfer process was proposed on the multilayer-cloth for perspiration based infrared camouflage, capable of predicting multi-dimensional and transient processes, and illuminating the influences of the related variables and ambient fluid field.;This research, as summarized above, not only built a good foundation for further structural optimization for perspiration based infrared camouflage, but also provided both theoretical and experimental guidance for future design of cloth systems dealing with coupled heat and moisture transfer for new functional properties.