Solar radiations reach Earth, a warm cup of coffee
We will start with heat transfer modes and proceed on to how it can be created artificially; we will conclude with benefits of artificial heat transfer.
There are three fundamental ways in which heat is transferred from one medium to the other, namely conduction, convection and radiation. In conduction, medium of transfer is a rigid body whose molecules are stagnant. The two rigid bodies are required to be in close contact with each other for heat transfer to take place via conduction.
In convection process, the medium that carries heat to or away from a body is a fluid and hence in motion. There are two sub-categories of convection called natural convection and forced convection. Natural convection occurs merely due to temperature difference while forced convection has an artificial source of air which carries heat.
The last primary mode of heat transfer is radiation and in this no medium is required for heat to flow just as radiations from sun reach Earth through vacuum.
Solar radiations are the main reason why the temperature increases or decreases in our environment; closer the Earth to Sun, warmer it would be. This heat uses conduction and convection to travel into our homes via windows and walls and makes the indoor temperature unbearable; similar is the case in industries and factories where outside temperature along with indoor sources contribute to the general rise in temperature of the vicinity.
An artificial flow of air is generally created by fans under the above mentioned conditions to have fresh air in circulation. An increased air flow accompanied with opened windows and doors keeps air in circulation and ensure ventilation which removes warm and stale air and allows fresh air to flow in.
In places where there are indoors heat sources like in furnaces and in kitchens (domestically speaking), exhaust fans are employed. They are installed in a hole made in wall at a height close to the roof and create an outward air flow. As hot air tends to rise, exhaust fans make it flow outdoors and clean the indoor atmosphere so that fresh air can flow in.