Heat Exchange

Heat can be transferred from one substance to another through many mechanisms. There are a few methods that can be regulated by mammals to maintain thermal homeostasis. For all methods, if the body temperature is higher than the surrounding environment, then heat is lost to the environment through the part of the circulatory system closest to the surface of the body. If the animal's body temperature is lower than the surrounding environment, then heat is transferred into the body. The magnitude of heat exchange is greater when the difference in temperature is larger.

Figure 1. Three mechanisms of heat exchange.

Convective heat exchange occurs when heat is transferred between the body and a fluid, such as air or water. The rate of heat transfer is proportional to the rate of fluid flow.

Radiation is the exchange of heat by radiative transfer. All surfaces emit radiation, with the magnitude of energy emitted being proportional to the surface temperature of the surface.

Conductive heat exchange occurs between a body and a surface it is touching. Bodies have adapted to use countercurrent exchangers in their circulatory system to reduce heat loss through conduction.