# Types of Heat Transfer: Convection

### Heat Transfer: Convection:

Convection is a process of transferring heat from one point to another through the movement of fluids. The points below are noteworthy with regards to heat transfer through convection:

1. A conductor or metal is usually required to transfer heat into the liquid before the boiling process can proceed through convection.

2. Convection explains the transfer of heat in liquids and gases.

3. The boiling process of water occurs through convection.

Below is an explanation on the processes involved in boiling:

• The water molecules inside the pot (yet to be boiled) possesses equal kinetic energy.
• When placed on a heat medium, for instance, gas cooker; the water molecules closest to the bottom and margins of the pot will begin to move or rotate as a result of heat transfer by conduction from the metallic pot. This is so because the pot is a metal and a conductor. As a result, the water molecules (closest to the bottom and margins of the pot) becomes hot.
• Due to the hotness of the water molecules closest to the bottom and margins of the pot, they expand and become lighter, thus gaining an increased ability to move (due to an increase in their average kinetic energy). As a result of their increased kinetic energy, they move to the top and center of the pot, displacing the water molecules that were initially there to the bottom.

The displacement of water molecules in the above paragraph is as a result of the difference in density of water molecules closest to the bottom and margins of the pot versus those at the top/center. Those closer to the bottom/margins of the pot are less dense (or lighter) than those at the top/center. This displacement movement of water molecules is sometimes referred to as the convection current.

The image below shows the convection current during the process of boiling:

The water molecules at the top and center of the pot have a higher density since they are farther away from the bottom and margins of the pot. Also, they have a lower kinetic energy when compared to those at the bottom and margins. They are therefore displaced downwards (since they have higher density and lower kinetic energy) by the water molecules at the bottom and margin of the pot which had now moved upwards and inwards.

The above process continues until the entire water molecules attain the same kinetic energy. At this point, thermal equilibrium is said to be achieved.

If the pot (containing the boiling water) remains on the cooking gas, the increased kinetic energy of the water molecules will eventually lead to the escape of water particles into the atmosphere via translational motion. At this point, the water in the pot reduces until nothing is left. This emptiness (of the pot) is a result of an increased kinetic energy of the 'now' gaseous particles. Understand that the water had changed its state from liquid to gas by now.

When heating a liquid, the heat energy produced by the particles of higher kinetic energy stimulates the liquid particles of lower kinetic energy (to an increased kinetic energy or rotational motion) until equilibrium is achieved.
Please read on the concept of heat transfer here to better comprehend translational, rotational and vibrational movements in particles).

It is important to understand that convection is the main method of heat transfer in water and air.

The process of increasing a room's atmospheric (or air) temperature through the use of a radiator occurs via convection. The image below shows this:

With regards to convection in air particles (using the above diagram); When we put on the heater or hot radiator (assuming it’s on the floor), the kinetic energy of the air particles closest to the heater will become increased.

The particles of this 'hot air' move upwards and sideways, mixing with the cooler air in these regions.

The net result of this rising hot air is the transfer of heat energy from a higher region to a lower region.

It is important to state that convection is achieved via the translational and rotational movement of matter. Translational and rotational movements are involved in gases and liquids respectively; and they result in the transfer of heat energy.

Meanwhile, always understand that convection is not achieved through the vibrational movement seen in solids.

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