Convection

Convection is widely the movement of any molecules via any fluid state comprising liquids and gases. It is the significant form of heat and mass transfer on earth and can be found in many systems around the world. Many people are familiar with convection form heating their food or their houses and it also plays a remarkable role in creating the climate conditions on the planet.

The two major categories

Convection can be categorized into two major types such as forced convection and natural convection. The forced convection takes place when the medium transporting the heat is moving on its own like when the air is being pushed by a fan. In such case, the heat is distributed by the movement of the air of fluid but actually it is not the cause of the movement. Forced convection is also sometimes known as heat advection.

The occurrence of natural convection

Natural convection takes place when the medium transporting the heat is being encouraged to move by the heat itself. This occurs both since medium enlarges as it heats up as in the case of gases and also because buoyancy sources the warmer fluid to go up. Natural convection is also sometimes known as free convection. And these two categories of convection both forced and natural happen regularly at the same time, where the heat is causing the fluid to move somewhat but it is also moving due to some other force. In such case it is referred to as mixed convection.

The occurrence of forced convection

Forced convection can be seen in many places in the world, both in man-made objects and in the natural world. For instance, a convection oven forces heated air to circulate through the oven by using a fan. Though the air might somewhat on its own, the forced convection allows for an even disbursement of heat. Inside the human body, the circulatory system is another great example of forced convection. Blood among its many uses, acts as both heating agent and cooling agent for the body and is forced through the circulatory system.

Natural convection can be tangible most easily by placing something above a non-fanned heat source like a radiator heater. As the air straight above the heater is heated, it increases since it is more buoyant than the cold air around it. When placing a piece of tissue paper above the heater one can see it gets carried upwards by the natural convection happening. Similarly, in a liquid one can see the same effect at work by heating up one liquid that is colored and placing it inside a colder liquid of a different color. The warm liquid will increase up through natural convection.

Questions:

• What is convection?
• State the role of convection.