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# Methods of Heat Transfer: Conduction, Convection and Radiation

Heat can be transferred through any matter, made up of atoms and molecules. At any given time, the atoms are in many states of motion. Heat or thermal energy is produced by the motion of molecules and atoms and it is present in all matter. The more molecules move, the more heat energy is released. When it comes to heat transfer, however, it simply refers to the process of transferring heat from a high-temperature body to a low-temperature body. Let’s understand that what is heat and what are the methods of heat transfer.

## What is Heat?

Molecules and atoms make up all the matter. These atoms are constantly moving in various directions (translation, rotational, vibrational). Heat or thermal energy is produced by the motion of atoms and molecules. This thermal energy exists in all matter. The more heat will be produced by the atoms or molecules if they move more. Heat is a form of energy that is necessary for life. Sun is the main source of heat on our planet.

## What is temperature?

Sometimes heat and temperature are mixed, as they are same but actually both are different. Heat is a form of energy that is caused due to vibration of atoms. On the other hand temperature is just a value that indicates that how much heat energy is taken by certain object. Temperature is the average value of energy of all the atoms that are present in that system.

## How is heat transferred?

The flow of heat from one system to another system due to temperature difference, is known as heat transfer, according to thermodynamics. For example if there are 2 objects. One is hot and other is cold. If both are made in contact with each other, then after some time both objects will be almost at same temperature. This is due to the heat transfer that happens from hot objects to cold objects. After this heat transfer, both bodies are in equilibrium with each other. The temperature difference is said to represent a potential that causes heat to travel from one location to another. Heat is sometimes referred to as flux.

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## Methods of heat transfer

When two systems have a temperature difference, heat will always find a way to flow from the higher to the lower system. There are three methods of heat transfer through which heat can be transferred from one location to another.

• Conduction
• Convection

To transfer heat, both conduction and convection require substance.

## What is conduction convection and radiation?

### What is conduction of heat?

Conduction is the transfer of heat between substances that are in direct contact with each other or it is the physical transfer of heat from stationary substance to moving stuff. The better the heat conductor, the more rapidly heat will be transferred. Metals are good conductors of heat. Conduction occurs when a substance is heated then its particles will gain more energy and their vibration speed will also rise. These molecules then bump into nearby particles and transfer some of their energy to them. This then continues and passes the energy from the hot end down to the colder end of the substance.

Thermal energy is transferred from a higher kinetic energy area to a lower kinetic energy area. When high-speed particles collide with slow-moving particles, the kinetic energy of the slow-moving particles increases. This is a common type of heat transmission that occurs through physical contact. Conduction is often referred to as thermal or heat conduction.

Examples of conduction include ironing the clothes, melting of ice when it is held in hands, putting a pot of water on burner and water starts to boil and many more.

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## What is convection of heat?

Convection also transports thermal energy from hot to cold locations but it is the in liquids. Warmer portions of a liquid or gas rise to cooler portions of the liquid or gas, causing convection. The warmer portions that have climbed higher are then replaced by cooler liquid or gas. As a result, the circulation pattern remains constant. Convection currents can be seen in the boiling water in a pan. The atmosphere is another wonderful example of convection. The sun warms the earth’s surface, causing warm air to ascend and cool air to move in.

Large-scale matter flow drives convection. The flow of hot air from the tropics to the poles, as well as the movement of cold air from the poles toward the tropics, create atmospheric circulation on Earth. A automobile engine is maintained cold by the flow of water with the water pump maintaining a flow of cool water to the pistons, is an example of convection.

While convection is usually more difficult than conduction, we can describe it and analyze its effects in a simple, realistic manner. Natural convection is caused by buoyant forces: when the temperature rises, the density of the air drops, causing it to rise. This principle holds true for any fluid. The pot of water on the stove, for example, is kept warm in this way; ocean currents and large-scale atmospheric circulation, on the other hand, move energy from one region of the planet to another.

During boiling of water, denser molecules stay in bottom of pan and less dense molecules come to the surface. Their collisions with each other make the water hot. In warm blooded animals, blood circulation occurs due to convection thus maintaining body temperature.

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## What is radiation heat transfer?

As opposed to conduction and convection, radiation is one of the methods of heat transfer that does not require any contact between the heat source and the object. In the process of radiation, no mass is exchanged and no medium is required. The heat emitted by the sun or the heat emitted by the filament of a light bulb are both examples of radiation.

Radiant heat is present in our daily life. Radiant heat is the term for thermal radiations. Emission of electromagnetic waves causes thermal radiation to be produced. The energy from the emitting body is carried away by these waves. Radiation occurs in a vacuum or through a transparent material, which might be solid or liquid. The random mobility of molecules in matter results in thermal radiation. Emission of electromagnetic radiation is caused by the movement of charged electrons and protons.

The thermocouple is a device that measures radiation heat transfer. Temperature is measured using a thermocouple. Heat transmission from a fire or the Sun can be felt. The space between Earth and the Sun, on the other hand, is mostly empty, with no chance of heat transfer via convection or conduction. Similarly, microwaves emitted in the oven, UV rays coming from sun and release of alpha particles during decay of uranium into thorium are examples of radiation.

Radiation is used to transmit heat in these cases. Electromagnetic waves emitted by a heated body are absorbed by our skin and do not require a medium to propagate.

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