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Convective heat transfer occurs through fluid motion and can be natural or forced. Natural convection is caused by varying densities of fluids, while forced convection uses external mechanisms like pumps and fans. Examples include boiling water and the circulatory system in animals.
Convective heat transfer is heat transfer by convection, the transfer of heat through fluid motion. Convective heat transfer can occur in two main ways: by natural convection and by forced convection. These two heat transfer methods are distinguished by the use or lack of external devices to move the heated fluid. In both cases, the heat transfer occurs via a fluid, such as a liquid, gas or reid, flowing over a solid mass.
An example of convection is boiling water in a pot. As the water near the heat source heats up, the molecules disperse. This causes the water to become less dense and more buoyant. The more buoyant water rises to the top of the pot and the cooler water takes its place. The cooler water will then be heated by the heat source, become less dense and rise to the top.
This process results in a current called convection current. In the case of boiling water, it becomes more visible when something like macaroni is in the pot: you will see the macaroni moving up and down with the convection current. Boiling water is an example of natural convection. In this system, nothing but the varying densities of water cause convective heat transfer. In fact, natural convective heat transfer works because, in general, heated liquids have lower densities than colder liquids.
Unlike convective heat transfer caused by natural convection, heat transfer is caused by forced convection. Forced convection differs from natural convection in the use of an external mechanism to move the fluid. This convective heat transfer method does not need the different densities of fluids to work. Some examples of external mechanisms used in forced convection are pumps and fans. The heart is a natural example of such a device used in forced convection.
The circulatory system is one of the ways humans and some animals regulate their body temperature. A heart is essentially a pump and blood is a heated fluid. The heart pumps the heated fluid through the blood vessels and to the skin. The heat is then removed from the body through various means. This is one reason many desert animals have large ears: blood is able to circulate through the ears, giving off its heat to the environment through various heat transfer methods.
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