On the use of porous materials to simulate evaporation in the human sweating process

The specific properties of porous materials when wet, namely the cooling effect near the surface due to the heat extraction during water evaporation, were known and used by ancient civilisations. During human perspiration, the necessary heat for sweat evaporation is provided by the cutaneous surface, which induces a temperature drop similar to that observed in a wet porous material. The potential for using porous materials to simulate human perspiration was investigated in this work using different permanently saturated porous materials (plaster, white clay and red clay). The existence and duration of a constant drying rate was studied, as well its dependency on the surrounding conditions, namely temperature, moisture and velocity. We verified the existence of a period with constant drying rate for all the tested samples; this is evidence that a uniformly distributed humid layer is formed and stays on the external surface of the porous body. This represents a step forward in simulation of the sweating mechanism. All three tested porous materials showed very good reproducibility and good sensitivity in terms of the response of the evaporation rate to any variation of the relative humidity.