Convection refers to the process of transfer of heat or energy through a fluid (gas or liquid) from high temperature to low temperature. Convection is one of the three types of heat transfer; the other two being radiation and conduction. Conduction refers to the transfer of heat between bodies which are in physical contact; whereas, in radiation, energy is emitted in the form of electromagnetic waves.
The molecular motion in fluids is the cause of convective heat transfer. The motion of the molecules increases when the temperature of the molecules is increased; as a result, the molecules tend to move away from each other. The movement of the molecules is responsible for the transfer of heat.
If you look around, you might observe that convection has an important role to play in daily life. In this article, we are going to discuss the real-life examples of convection which are quite interesting.
The formation of sea and land breeze form the classic examples of convection. Going by the definition of convection, the molecules at a higher temperature displace the ones at a lower temperature. Similarly, in the afternoon, the surface of the land near the sea is warmer as compared to in the evening. Convection causes the air, which is closer to the land surface, to heat and, hence, rise. This warm air near the land is readily replaced by the cool air resulting in “Sea Breeze.” When its night, the tendency of land to cool down is more. However, the air above the sea water is warm and, therefore, rises up. Once this air rises, it is replaced by the cool air from the land, which is commonly referred to as “Land Breeze.”
2. Boiling Water
Convection comes into play while boiling water. What happens is that the cold water at the bottom heats up from the energy from the burner, and rises up. As the hot water rises, the cold water rushes in to replace it, which results in motion in the circular fashion.
3. Blood Circulation in Warm-Blooded Mammals
You might be surprised to know that warm-blooded animals employ convection to regulate the temperatures of the body. The human heart is a pump and blood circulation in the human body is an example of forced convection. The heat which is generated by the cells in the body is transferred to air or water which is flowing over the skin.
On a hot summer day, air-conditioners are used constantly. The process of cooling air in air-conditioners employs the very principle of convection. The air which is cold is released by the air-conditioners. Now, this cold air is denser than the warm air, and, hence, it sinks. The warm air, being less dense, rises and is drawn in by the air-conditioner. As a result, a convection current is set up and the room is cooled.
Even the radiators work on the principle of convection. Just like the example of air-conditioners above, the radiators also work in a similar fashion. In radiators, the heating element is placed at the bottom. The cold air, being dense, sinks and is taken into the radiator; it is warmed and released. The hot air replaces the gap left by the cold air. Therefore, a convection current is set up.
The working principle employed by the refrigerators is very much similar to that of the air-conditioners. The freezer, in case of refrigerators, is placed at the top. As mentioned above, the warm air, being less dense, rises up and, hence, it is cooled down by the freezer. Now, this cool air, being denser, sinks and, therefore, keeps the lower part of the fridge cool.
7. Hot Air Popper
The hot air popper which is used to make popcorn also utilises the principle of convection. The hot air popper has a fan, vent, and a heating element. When the popper is turned on, the fan is employed to blow air on the heating element through the vent. The heating element, in turn, warms the air; which then rises. Above the heating element, the popcorn kernels are placed. The kernels are heated when the hot air rises; therefore, resulting in the popping of the kernels.
8. Hot Air Balloon
The reason why hot air balloons are able to rise up is because of the principle of convection. You might have seen the heater at the base of the balloon. This heater heats up the air, which moves upwards. The hot air which rises get trapped inside the balloon, and, hence, causes the balloon to rise up too. When the landing of the hot air balloon has to take place, some of the hot air is released by the pilot. The cold air replaces the hot air released; therefore, the balloon lowers.
9. Hot Beverage
Who doesn’t like a hot cup of coffee on a winter day? Do you know the release of the heat from the steaming hot cup of coffee also works on the principle of convection? You might have often observed the steam coming out from the hot cup of coffee. The steam, in the form of warm air, rises because of the heat of the fluid. This steam is transferred to the air.
10. Rainfall & Thunderstorms
One might even get to observe the role of convection in rainfall and thunderstorms. Let’s see how? Clouds are formed when water in the ocean gets warmed and rises up. These warm water droplets, in turn, saturate which lead to the formation of clouds. The small clouds which are formed by this process collide with each other to develop bigger clouds. These large clouds which are commonly referred to as cumulonimbus result in rainfall and thunderstorm.
11. Air-Cooled Engines
Engines in vehicles like cars are cooled by water jackets. Prolonged running of the engines leads to the warming of the water in the water jacket/water pipes which surround the engine. In order to keep the engine running, the water must be cooled down. When the water heats up, it starts to flow in the pipes which are present around the engine. When the warm water flows through these pipes, it is cooled down by the fans. These fans are also present in the pipes. Once the water cools down, it flows back into the engine; hence, obeying the very principle of convection and cooling the engine down.
12. Melting of Ice
The melting of ice is yet another example of convection. The temperature of the surface or boundary of ice increases as warm air blows over the surface; or water, which is at a higher temperature as compared to the ice, flows underneath it. As the temperature of the surface or boundary of ice alters, the ice melts. In a similar fashion, a frozen material thaws when kept in water.
13. Convection Oven
Who doesn’t like cakes and cookies? But do you know most of the ovens utilize the principle of convection? In the case of convection ovens, forced convection is employed. With heating, the molecules present in the air also get heated up and start moving. The food inside the oven is cooked due to this warm air.