QS Study

Heat loss through evaporation and respiration increases in dry, windy weather conditions. Body temperature is the property of the body that determines whether or not the body is in thermal equilibrium with the environment. A very low body temperature (hypothermia) can be serious or even deadly. Low body temperature usually happens from being out in cold weather.

The process of heat loss from the body: Heat is lost by-

(1) Radiation

Transfer of heat from one object to another without any contact is called radiation heat is transferred as an electromagnetic wave. This normal process of heat moving away from the body usually occurs in air temperatures lower than 68°F (20°C). About 60 % of total body heat is lost by radiation.

(2) Conduction

Transfer of heat from atom to atom or molecule to molecule by traction of kinetic energy is called conduction. By conduction total body heat loss is 18% (to air 15% and to solid object 3.1%). However, water causes more heat loss from the body than air does, so heat can be lost from the body very quickly when it is placed in cold water.

(3) Convection

Transfer of heat by movement of a molecule of a fluid or gas is called convection. Here a change of layers of air takes place close to the skin. The body loses 10% to 15% of its heat through convection.

Fig: Mechanisms of heat loss from the body

(4) Evaporation

Evaporation of water from your skin if it is wet (sweating). About 22% heat is lost in this process. It includes –

  • Insensible loss through skin and lungs at a rate 12 – 16 cal/hour.
  • Sweating: 0.58 kcal heat is lost for each gram of water evaporation.

(5) Other

Heat is lost through urination and deflection.