# Heat transfer- Convection

Convection is the movement or transfer of heat from one place to another in the form of fluids and this is the most dominant form of heat transfer in the form of gasses and fluids. The convection is forced by the movements of fluids by means other than buoyancy force as we take the example of a water pump in an automobile engine and by this it is concluded that thermal expansion of fluids may also force convection to explain this let us take an example of the draft in the chimney or around any fire as in natural convection an increase in temperature produces a reduction in density which in turn causes fluid motion due to pressure and force and for this we can take an example of water which is heated on a stove in this hot water from the bottom of the pan rises which displace the colder dense liquid which falls.

## Types of convective heat

There are two types of convective heats which include natural or free convection and forced convection. Free or natural convection itis when fluid motion is caused by a force called buoyancy forces that result from the density variations and due to the variation in the thermal temperature in the fluids. More familiar examples are the upward flow of air due to the fire and hot object or the circulation of water in the pot that is heated from below.

Forced convection is when a fluid is forced to the flow over the surface by an intense source such as fans, by stirring and pumps or creating an artificially induced convection current. The internal and external flow can also be classified as convection as internal flow occurs when a fluid is enclosed or stopped by a solid boundary such as flowing through the pipes. Just like that, an external flow occurs when fluid extends indefinitely without reaching or enclosed by a solid surface. Other classifications can be made depending on the smoothness and undulations of the solid surface.

## What is Newton’s law of cooling?

Convection cooling is also known as Newton’s law of cooling and it states that the rate of heat loss of a body is proportional to the difference in the temperature between the body and its surroundings under the effect of the breeze. In this, the heat transfer coefficient depends on the temperature and it’s not a reality when the temperature changes.