Definition of Convection, Characteristics, and Examples – Definition of Convection is a natural process where heat is transferred between two liquid substances, two gaseous substances, or between gaseous and liquid substances as long as they are at different temperatures.
In fact, this convection is also referred to as the transfer of heat between gases and solids or between liquids and at different temperatures. But there is still a lot we need to know about convection and in this article, we will discuss it more fully.
Meanwhile, conduction is defined as the transfer of heat between two objects when they are in the same box. The contact meant here is physical contact. In addition, conduction is also often referred to as diffusion.
Well, before we look into some examples, let’s first understand the basic information related to convection. Starting from the meaning of convection, characteristics, and examples:
Definition of Convection
Convection is a term related to physics or more precisely fluid mechanics. The concept of convection itself also has a literal meaning, which is the transfer of heat through a fluid, both in liquid and gas form caused by molecular motion. The movement of molecules that transfer heat can be of two types, namely in large numbers or in individual particles. The first is called advection and the last is called diffusion.
That is the principle of heat transfer that works not only in liquid and gas cases as discussed above. But also in solids too. However, the difference between the two is that heat transfer in solid form is called conduction.
An example in everyday life is the form of electronic goods that work on radiation, microwaves, and so on. The following are some examples of convection that need to be understood.
Characteristics and Examples of Convection
After knowing the meaning of convection, here are some examples of convection around us, including microwave ovens, melting ice cubes, and hot air balloons. Let’s discuss one by one to make it clearer:
1. Microwave Oven
Microwave ovens are one of the most common examples of convection-derived kitchen appliances. This tool works using the principles we have discussed above and we can notice that this tool is usually used to warm a plate of food.
Then, what actually happened in it. So, what happens is that the air in the microwave will be heated and then convection currents are forced into the food inside.
If you place a bowl of soup or a cracker, then you will see that the soup liquid will boil like boiled while the cracker will expand like when we fry it.
2. The melting of ice
The melting of ice is another example of convection that we can see in everyday life. The change of ice from a solid cube to a liquid form occurs due to the hot temperature around it. The temperature of the space around the ice is usually higher than the temperature of the ice itself.
While heat waves or heat currents have a tendency to flow from higher to lower temperatures. That means, the hot temperature in the room flows through the ice. Until that causes the ice to change its shape into a liquid. This principle remains the same as in the case of storms or tornadoes.
3. Air Balloon
The last example is a hot air balloon. By using the principle of convection, hot air balloons will be seen rising above the ground and floating in the air. This mechanism is that the fire inside the balloon will heat the air inside and not let the air out of the area inside the balloon.
As we know that heat transfer occurs when there is a temperature difference between two objects that are in direct contact. That’s when the flow of heat from the body appears from the highest temperature to the lowest temperature. Whether it is a liquid or a gas, both are considered fluids and molecular motion is responsible for naturally transferring heat.
Poor thermal conductivity makes forced mass transfer necessary to extract or transfer heat. Either by heating or cooling liquids or solids.
We can see this in boilers that use a heat exchanger made up of metal pipes, where water will circulate inside and gas at a very high temperature outside.
Gases that have a hot temperature will circulate in one direction. This will later produce heat by convection into the metal tube and receive it by conduction.
Then the tube heats up and produces heat by conduction to the water, which circulates in the other direction and receives heat by convection, heating into steam.
Examples of Convection in Everyday Life
Here are some examples of convection in everyday life.
- Boiling water: Here the heat will transfer from the stove to the pot by convection, then heat the water from the bottom. After that, the hot water will rise and the cold water will descend to replace it, this causes a twisting motion.
- Radiator: Places warm air at the top and draws cold air by convection to the bottom.
- A warm cup of tea: The steam that comes out shows the heat transferred to the air by convection.
- Ice melting: Heat that moves into the ice from the air by convection. This causes the ice to melt from a solid to a liquid.
- Thawing frozen food: Frozen food will thaw faster if it is under cold running water when placed in water. This action of flowing water will transfer heat into the food by convection and faster.
Examples of Convection in Meteorology and Geology
The following are some examples of convection originating from Meteorology and Geology.
- Convection mantle: The rock mantle inside the Earth moves slowly due to convection currents that transfer heat from the interior of the Earth to the surface. This is one of the reasons why tectonic plates move slowly around the Earth.
- Oceanic Circulation: The warm water around the equator will circulate by convection towards the poles and the cold water at the poles will move towards the equator.
- Stack effect: This stack effect is also called the chimney effect. Where this is the movement of air in and out of buildings through convection, chimneys or other objects due to buoyancy. In this case, buoyancy will refer to the difference in density in the air between the air inside and outside. This buoyancy force will increase because the higher the structure and the greater the difference between the heat levels inside and outside the air.
- Stellar convection: Stars have convection zones where their energy is moved by convection. Outside the core is the radiation zone where the plasma moves. Currents from convection will form as the plasma rises and the cooled plasma descends.
- Gravitational convection: This is shown when dry salt diffuses into wet soil because fresh water floats in salt water.
- Forced convection: An example of this convection is in the pump or suction device used to facilitate convection as well as in the fan.
Types of Convection
Below is some information about the types of convection that may add to the reader’s knowledge of matters related to convection.
1. Forced Convection and Natural Convection
It should be understood that convection can occur naturally or what is called “natural convection” or due to the presence of moving devices “forced convection”.
An example of forced convection is a fan. A fan is a device that can produce air movement artificially. Where the air in it moves due to the rotation of the fan. While for example natural convection usually occurs because the fluid is lighter when it is hot and becomes heavier when it is cold.
So when the fluid has a hot part and a cold part, then the hot part will naturally move up and for the cold part it will naturally move down.
For example, when the water in the pan is heated, then the water at the bottom will be hot because it is near the fire, then the hot water will move from the bottom to the top surface. At the same time, the water on the top surface tends to be colder so it will move to the bottom of the pan.
2. Gas Convection
When a hot object is surrounded by cold air, the heat will transfer to the air by convection with direct contact. The process is similar but when warm air surrounds a colder object, then the air will become colder when heat is transferred to the object by convection.
3. Fluid Convection
A similar convection process can also occur in liquids. Although at a slower speed according to the viscosity of the liquid. However, it cannot be assumed that the convection in the liquid will result in colder components sinking and warmer ones rising.
Convection of this fluid depends on the fluid itself and the associated temperature. Water will reach its greatest density which is around 4 degrees Celsius. Therefore, in a pool of water, it initially has a temperature of 4 degrees Celsius, where every part that is hot will rise to the top.
If there is a cold part below 4 degrees Celsius, it will rise to the top and the warm water will sink to the bottom.
4. Earth’s Atmospheric Convection
Convection heat transfer will produce wind and air currents. Because during the day, the sun will heat the ground, which will give up some of its energy to the air through conduction and heat with convection. As the air warms, its density will decrease and become lighter.
Colder air will descend, because it is heavier and has a higher density compared to hot air. Part of the hot air will rise and create the current and the rest will move horizontally creating wind.
Hot air that has risen very high will release this heat at night, preventing global warming, and regulating the Earth’s temperature.
Differences in Conduction, Convection, and Radiation
Heat transfer is the physical action of thermal energy that is exchanged between two systems by removing heat. Temperature and heat flow are the basic principles of heat transfer. The amount of heat energy available will be determined by the temperature and the heat flow will represent the movement of heat energy.
In simple terms, heat transfer can be divided into three major categories, including conduction, convection, and radiation. Here is the full explanation:
1. Conduction Process
This conduction will transfer heat through direct molecular collisions. Areas of greater kinetic energy will send heat energy to areas with lower kinetic energy.
High speed particles will collide with slower speed particles. Where particles that have a lower speed will increase the kinetic energy as a result.
Conduction is the most common form of heat transfer and usually occurs through physical contact. For example you put your hand to the window or metal to the open flame.
This heat conduction process depends on the following factors, among others, the temperature gradient, the length of the travel path, the cross-section of the material, and the physical properties of the material. This temperature gradient is a physical quantity that describes the direction and speed of heat travel. Where the temperature flow will always occur from the hottest to the coldest. After finding a thermal equilibrium between the two temperature differences, the thermal transfer will stop.
The cross-section and also the travel crossing, both will play an important role in the conduction process. The larger the size and length of the object, the more energy is needed to heat it. Then the larger the exposed surface area, the more heat will be lost.
Smaller objects with a small cross-section will have minimal heat loss. This physical property will determine which material can transmit heat better. Specifically, the coefficient of thermal conductivity will determine that the metal material will conduct heat better compared to when it comes to conduction.
2. Convection Process
When fluids such as air or liquid are heated and then move away from their source, they will carry heat energy. This type of movement is called convection. The liquid on the hot surface will expand, become less dense, and rise.
At the molecular level, molecules will expand after the introduction of thermal energy. When the temperature of a given mass of liquid increases, the volume of the liquid must increase by the same factor. The effect that exists on the fluid will cause displacement. When hot air rises, it will push denser, cooler air downwards.
3. Radiation Process
Thermal radiation is produced from the emission of electromagnetic waves. The wave will carry energy from the emitting object. Then radiation occurs through a vacuum or transparent media, whether solid or liquid.
This thermal radiation is the result of the random movement of atoms and also the matter in the matter. The movement of protons and charged electrons will produce the emission of electromagnetic radiation. All materials will emit heat energy based on their temperature.
The hotter an object is, the more it emits. The sun is one of the clearest examples of heat radiation that sends heat through the solar system.
This is a commentary on the meaning of convection, its characteristics, and examples.