28.20 : Mechanisms of Heat Transfer

Heat transfer between the human body and its environment occurs through four main mechanisms: conduction, convection, radiation, and evaporation.

Conduction, accounting for approximately 3% of body heat loss at rest, is the process of exchanging heat between molecules of two materials in direct contact. This can result in both heat loss and gain. For instance, when the body is submerged in water, which conducts heat 20 times more effectively than air, it can either lose or gain significant heat. Convection involves heat transfer via the movement of air or water between areas of different temperatures. The rate of convection increases with the speed of the moving air or water. Radiation involves heat transfer in the form of infrared rays between warmer and cooler objects without physical contact. If surrounding objects are warmer than the body, the body absorbs more heat than it loses. Evaporation converts liquid to vapor, taking away significant heat in the process. This mechanism also plays a crucial role in preventing overheating during exercise. Additionally, continuous evaporation from the lungs, oral mucosa, and skin leads to insensible heat loss, contributing to basal heat regulation.