What is the difference between Natural and Forced Convection

The question is:

using physical parameters of the fluid distinguish clearly between:
i) Natural convection
ii) Forced convection

Thanks for any help!

Natural convection is the movement that is powered by gravity, and the fact that warmer fluids and gases change density when they are heated. Heavier cooler fluid forces its way downwards, pushing the warmer, less dense fluid up: sort of "out of the way".

Forced convection is when the fluid or gas is pumped or blown by an external force.

Hi Niall Darragh!

According to
http://wiki.answers.com/Q/What_is_the_di…

Natural Convection occurs when a warmer less dense fluid is pushed away by a cooler denser fluid. Forced Convection occurs when an outside force pushes a fluid, such as water of air, to make it move and tranfer heat. A fan is a perfect example... An air conditioner is definitely an example.