Problem
Two T-shirts, identical in shape, one cotton and one wool, are worn against the skin of a sweating athlete. The cotton T-shirt soaks up water, while the wool one stays almost dry. Which of the two fabrics cools the skin more, and why?
Solution
Wool cools more, contrary to what intuition about the “cooler-feeling” fabric might suggest. In cotton, sweat is absorbed and carried away from the skin: the water evaporates from the soaked fabric rather than from the skin, drawing latent heat mainly from the air and the cloth. In wool, which stays dry, the sweat instead remains on the skin and evaporates directly from it. In this way the latent heat of evaporation is drawn away exactly where it is needed, i.e. at the body’s surface, whereas in wet cotton conduction and water removal prevail. The fabric that cools more is the one that lets sweat evaporate directly from the skin, i.e. wool (Bloomfield 2016) Riferimenti bibliografici.
Collegamenti
Argomenti: Termologia Concetti: Calore latente e cambiamenti di stato · Trasmissione del calore