In natural or free convection heat transfer mechanism, the flow of fluid takes place when there is a difference between the body and the fluid temperatures. The difference in density between the cold and hot fluids in the region causes the hot fluid to move in the upward direction. The force causing this flow is known as buoyancy force. The natural convection heat transfer coefficients are usually very low. Natural convection heat transfer mechanism is applied in many fields of engineering for cooling purposes. The free convection mechanism involves transferring of heat, for example, from electric transformers, rectifiers, pipes carrying refrigerants and steam, walls of the furnaces, and from the walls of ...