Explain heat convection.

Explanation

Propagation of heat in fluids is due to heat convection.
When fluid is heated from bottom, the volume of the fluid of that part increases and consequently density decreases.
Due to force of buoyancy light fluid rises upward and the cooler fluid, moves down to take its place.
The whole fluid gets heated as a result of such continuous process. This process of heating is called the ..heat convection...
Heat convection can be natural or forced.
Natural convection : If the motion of fluid takes place due to difference of density, it is called natural convection.
In atmosphere, hot and cold air currents are formed by natural convection due to unbalanced heat flow.

Forced convection : If the motion of fluid takes place with the help of some device like pump, fan, stirrer etc. it is called forced convection.
In human body, the heart acts as a pump and by circulating blood in all parts of the body, it maintain temperature of the body forced convection.