Physics of Heat Exchange with the Environment

Abstract

The four modes of heat exchange between an animal and its terrestrial environment are conduction, convection, radiation and evaporation. The rates of heat transfer (watt) by all modes are proportional to the area at which the transfer takes place. Thus, as far as the skin is concerned, the rates are expressed per unit surface area (W·m^-2). In a first approximation, the rates of heat transfer by conduction, convection and radiation are proportional to the temperature difference between the surface and the environment; it follows that the physical features of these three processes are described per unit temperature difference (W·m^-2 ·ºC^-1). In the case of evaporation on the skin, the water vapour pressure difference (kPa) between the body surface and the ambient air substitutes for the temperature difference.