Convection happens when heat is moved through a gas or liquid by the material of a hotter substance moving to a cooler area. Find out what convection is and explore several different examples of it.
What is Convection heat transfer?
Convection is the transfer of heat through the movement of molecules in a fluid.
Heat is first transferred by conduction between the object and the fluid, while the bulk motion of the fluid provides the contour.
- Being the process of heat transfer in liquids and gases, convection involves the agitative motion of the particles. There is a large-scale movement of particles in the liquid.
- It performs in both gas and liquid with a resultant circulating motion.
- Convective heat transfer can be either natural or forced.
- Heat can be transferred in three ways: conduction, convection, and radiation.
Imagine a liquid being heated from below. The lower sections of the liquid get heated and become less dense.
Because of buoyancy, an upper layer of fluid is displaced. The colder fluid then replaces the upper block that was previously denser but warmed and allowed to rise. This fluid is then heated and becomes even less dense. This phenomenon is what causes convection.
How is Heat Transferred through Convection?
When a segment of a fluid is heated from the bottom, it undergoes thermal expansion. The hotter parts of the fluid, which contain lower regions, become less dense.
It is a fact that lower fluid is more dense. From the standpoint of buoyancy, the hotter part of the fluid, which is less dense and hotter, rises.
Then, the chilled part, which is a dense fluid, takes its place. This process continues, whereby the portion that is exchanged gets heated and moves further up, while the portion above succumbs and is substituted by the upper layer. That is how heat is relayed through convection.
Types of Convection Heat Transfer
Convection is further divided into two sub-groups: natural or forced.
#1. Natural convection
This occurs because of buoyant forces due to density difference, which is associated with or caused by a combination of temperature unevenness.
When the fluid in question has set onto a surface that is hot, its molecules tend to get dispersed, which causes a decrease in density.
1. Water boiling.
This is classified as one of the best examples of natural convection. The heating of water is caused by the boiling of water molecules located within the pot, which causes the water molecules located at the base of the pot to warm up and expand.
The colder molecules are dense, which is why they move down, creating a circular flow. This constant circulation creates a convection current, transferring heat through the pot and into the water until it boils.
2. Circulation of air inside the room.
Have you ever thought of how the whole room gets warm with a heater present? It is another example of natural convection.
The heater warms the air in its proximity, making it less dense, and is then displaced upward by cooler, denser air. This creates a convectional current that allows the whole room to get warmer over time.
Many other natural phenomena, such as sea breezes and moves of tectonic plates, also are the several areas which phenomena which involves processes and convection heat transfer.
#2. Forced convection.
This is when the fluid undergoes forced flow from an outside source such as a water heater, pump, or fan.
Forced convection examples:
- Use of fans to cool down the room: A fan circulates the air and forces it across cooler surfaces, which helps to reduce the heat from warmer objects, decreasing the temperature of the room.
- Convection ovens: These ovens employ fans to better circulate hot air to food so that it is warmed on every side evenly. This is a great example of the application of convection heat transfer theory to cook food.
- Car radiators: The liquid coolant is cycled through the engine and takes in heat, then it goes to a radiator where a fan blows air, which removes the heat into the surroundings. This keeps the engine from overheating and ensures it operates in the optimal temperature range.
Some other examples of forced convection include hair dryers and HVAC systems. To dry hair, a hair dryer uses a heating element to warm air and a fan to blow the warm air onto the head.
In the same way, HVAC systems use blowers to move air over cooled or heated coils, then blow the cooled or heated air into buildings.
Examples of Convection in Real Life
As we have already seen, there are two kinds of convection. Now, let’s take a look at some examples of convection. In this part, we grouped all of the examples into two parts based on their types.
#1. Boiling Water.
This is the most familiar and relatable household example of convection.
Let us first take a kettle of water. As the kettle heats the water, we know that water expands. We see the water on the bottom “curling” due to buoyancy.
The water on the top layer is cooler, which causes it to move, plus it gets heated. This cycle repeats until all the water reaches the boiling point.
#2. Air-Conditioner.
On one of the hottest days of the summer, air-conditioners are always ON. The way air is cooled in air-conditioners is due to the principles of convection.
After the air is cooled, it is then released from the air conditioning unit. The released air has a lower temperature in comparison to the air in the space. So, it will sink.
The other air, which is at a higher temperature, will replace the air and take the place of the sunken air. As a result, it will be sucked into the air conditioning system and convection current will occur which will cool the room.
#3. Radiator.
A motor radiator is a device used in a vehicle or machine designed to cool the hot liquid that passes through the block of an internal combustion engine.
In automobiles, this liquid is called coolant. Through the radiator tubes, hot coolant is brought to the radiator. When driving, cool air from the surrounding area also enters the fins of the radiator.
The flowing air over the radiator fins assists in cooling down the hot coolant the same way a car radiator cooling system works. The coolant cools off a little before passing through the engine, where it is again heated and sent back to the radiator.
The transfer of heat from the hot coolant to the cool air occurs through convection and continues the same way so that the air cooled is radiated out into the surrounding air.
Radiators can be considered as having two methods of heat transfer: convection and radiation. The first method, convection, moves heat from the coolant to the air in the surrounding region using the radiator fins,
while the second, radiation, moves the heated air to the surrounding atmosphere. This leads us to a different question.
Why should we consider two methods of heat transfer, convection and radiation, and say that these are car radiators instead of car convector designs?
The answer is missed on logical thinking. The explanation lies in the structure, which means fins that surround the mechanical device, which is called radiators instead of convectors. Car radiator heat removal is convection-controlled in nature.
#4. Refrigerator.
A refrigerator and an air-conditioner function on similar principles. For a refrigerator, the freezer is on top.
As stated earlier, warm air rises because it has less density relative to cool air. It is then cooled down by the freezer. Cool air is denser; as a result, cool air sinks and maintains the lower part of the fridge cool.
#5. Hot Air Popper.
The hot air popper, which is used to make popcorn, also utilises the principle of convection. The hot air popper consists of a fan, a vent, and a heating device. When the popper is on, the fan blows air onto the heating device through the vent.
The heating device also heats the air, which causes it to rise. The popcorn kernels are preheated above the heater. The rising hot air causes the kernels to pop.
#6. Hot Beverage.
Staring at a steaming beverage is an example of convection in action. You might have noticed a steam cloud above a cup of hot tea or coffee. Because of the fluid’s temperature, it causes the air above it to rise. We refer to this rising air as steam.
#7. Hot Air Balloon.
The hot air balloon has an interesting mechanism for movement. The pilot should set a heater that generates a lot of heat in the hot air balloon for the balloon to move.
The hot balloon rises to the balloon on its own accord when the air is heated. The balloon does not have access to the outside openings where hot air can escape.
To come down, you have to release some hot air. When the hot air is released, you will allow cooler air to take its place. That is how the balloon moves down.
#8. Air-Cooled Engines.
The majority of vehicles like cars have their engines cooled through the use of water jackets. Heated water tends to run for a long time, and there is water in the water pipes that encircle the engine. In order to start the engine, the water has to be cooled.
Now, when the water heats up, it has a tendency to gurgle within the pipes that are surrounded by the engine. Air is chilled while passing through these pipes, hence cooling the warm water present in the hoses and pipes attached to the engine.
Fans are also placed in the pipes. The very principle of convection is used, in limpid terms, once the water is cooled and passes back to the engine; the engine will end up cooling.
#9. Convection Oven.
Who doesn’t enjoy a good cake or a cookie? Did you know that most ovens use convection? In the case of convection ovens, forced convection is used.
Aeration in the oven leads to the increasing temperature of air molecules, resulting in their movement. The food is prepared in the oven by warm air circulating it.
#10. Blood Circulation in Warm-Blooded Mammals.
You may not believe it, but warm-blooded animals use convection for temperature control.
A human’s heart is like a pump that keeps blood circulating in the body flowing – this system is an example of forced convection. Heat produced within the cells of the body is lost to the atmosphere or water in contact with the surface of the body.
#11. Land and Sea Breeze.
This type of convection happens spontaneously and is alternatively classified as natural convection or free convection.
During the daytime, the land heats up more quickly than the nearby sea, resulting in the sea air being cooler in temperature than the land surface. Therefore, the heated air molecule moves up, and it’s replaced by cooler air.
That leads to the development of what we call “Sea Breeze.”
When this set of movements is repeated over time, there will be a continuous circulation or convection current, which we alternatively refer to as a convective current. During nighttime, the air that lies above the sea is warmer than the air lying over the land.
The warm air above the sea is replaced by cooler air from the land; thus, regions including the sea experiencing a replenished substitute of lower temperature air results in what we also term “Land Breeze.”
The question treating “Why land and sea breeze natural convection” is simple.
As has been established, Land and sea breezes are termed natural convection because we can explain it as a natural phenomenon whereby the current forces used to move the air are not man-made but depend on the movement of air due to temperature differentials.
In simpler words, the case works for the equilibration of the whole system encapsulated in the air surrounding Claims self-sustaining feedback loop system constitutes a process requiring no efforts of outside interference, mechanically refining without negating or destroying balance to biodiversity.
#12. Rainfall & Thunderstorms.
Cumulonimbus or thunderstorm clouds are the end result of all processes preceded by small clouds colliding with one another. These processes start with evaporation, where warm ocean waters transform into saturated water droplets that form clouds.
#13. Melting Of Ice.
Convection serves as the basis of yet another phenomenon: the melting of ice. Convection is caused by warm air blowing into contact with a body of water, as well as the water itself being at a higher temperature than the ice below it.
The application of heat to water causes the ice to melt. The ice melts when the surface or boundary temperature increases, and similarly, frozen material thaws in water.
#14. Convective Clouds.
When a significant amount of moisture is present in the atmosphere, convection currents lift the moisture into the sky, where it can form clouds.
The end result of sufficient droplets accumulating in the cloud is precipitation as convective thunderstorms.
#15. Squall Lines.
This type of convective thunderstorm is referred to as a squall line. Powerful wind and rain are associated with a line of thunderstorms formed by this convective phenomenon.
#16. Supercell.
A supercell represents an advanced level of a convective thunderstorm. This storm type tends to last for a long period (1 hour or more), and the probability of a risky tornado forming within it is high.
#17. Mantle Convection.
The convection currents transferring heat from the Earth’s core to its surface result in the slow movement of the Earth’s rocky mantle. This is why the tectonic plates move slowly around the globe.
New material is added from the growing side of a plate; then, it cools. On the consuming side, the material becomes dense due to heating and contracting and sinks into the Earth at an ocean trench. This creates volcanoes.
#18. Gravitational Convection.
Since fresh water is less dense than salt water, dry salt sinks into wet soil. This is a type of gravitational convection.
#19. Oceanic Circulation.
Convection results in the constant global circulation of the oceans. The warm water near the equator flows towards the poles while the cooler water at the poles flows towards the equator.
These examples of convection demonstrate how convection exists in both man-made and natural phenomena.
With a different understanding of convection now, broaden your understanding of other scientific concepts.
Convection Examples in Meteorology
Most weather phenomena are developed as a result of convection. From the perspective of meteorology, convection refers only to the vertical movement of an air parcel in the atmosphere. This definition may appear straightforward, but under certain conditions, it can create violent weather.
1. Convective Clouds.
If the air is humid, the convection currents will transport that moisture into the sky to form moisture convective clouds.
Thunderstorms are initiated due to the buildup of precipitation in the clouds and are referred to as moisture convective thunderstorms.
2. Squall Lines.
A type of moisture thunderstorm is referred to as a squall when it propagates in a system of organized thunderstorms. A squall is a type of moisture storm.
Squall lines are a kind of moisture thunderstorm system. They are characterized by the formation of a series of convective clouds and are associated with strong winds and heavy rain.
3. Supercell.
An example of a severe moisture thunderstorm is a supercell. This type of thunderstorm is reasonably classified as a supercell when it continues for a long time, 15 minutes or more, resulting in the formation of highly dangerous tornadoes.
Examples of Convection Related to Air Movement
In comparison to more commonplace examples of convection like household activities and weather phenomena, there is an entire other list of examples that are lesser known but specifically deal with convection as air movement.
1. Hot Air Balloon.
The pilot will release some of the hot air when he wants to descend the balloon. This will be replaced with some cool air, which causes the balloon to lower. The air trapped inside the hot air balloon moves upwards as the air inside is heated up by the heater.
2. The Stack Effect.
Also referred to as the chimney effect, the stack effect is the flow of air into and out of a building, flue, or similar object due to the action of buoyancy forces.
In this case, buoyancy refers to the variances in the density of the air above the air inside a given structure and the air outside the structure.
Due to the greater height of the structure and the greater difference between the temperature of the inside and outside air, the buoyancy force increases.
Convection Examples Related to Geology
Geological convection impacts the world profoundly, even though it is not directly observable. There are several phenomena in nature that are related to geological convection processes.
1. Mantle Convection.
The mantle of the Earth is solid but moves slowly as convection currents transfer heat from the Earth’s interior to the surface.
The gradual movement of tectonic plates on the earth’s surface is caused by the addition of hot materials at the growing edges of a plate, where it subsequently cools.
At the consumption edges, dense material that has been heated contracts and sinks into the Earth at an oceanic trench. This process initiates volcanic formations.
2. Gravitational Convection.
An example of gravitational convection is the downward diffusion of dry salt into wet soil, given that fresh water has ever so slightly lower density than salt water.
3. Oceanic Circulation.
The circulation of the world’s oceans is caused by convection. Warm equatorial water moves toward the poles while cooler polar water flows toward the equator.