Heat Transfer: Radiation

Heat can be transferred through any matter made up of molecules and atoms. At any given time, the atoms are in many states of motion. Heat energy or thermal energy is produced by the motion of atoms and molecules, and it is present in all matter. The heat energy is directly proportional to the amount of molecular movement. This means that the more the molecules can freely move, the more heat energy it contains.

What is Heat transfer?

The movement of internal energy from one substance to another is known as heat transfer. The study of heat transfer and the changes that occur as a result of it is known as thermodynamics. Understanding heat transfer is essential for comprehending thermodynamic processes like those found in heat engines and heat pumps.

Types of Heat Transfer

The internal energy of a substance is created by the motion of atoms and molecules, according to the kinetic theory. Heat energy is a type of energy that allows energy to be transferred from one body or system to another. This heat transfer can occur in a different variety of ways, including:

1. Conduction
2. Convection
3. Radiation

Here we will discuss the Radiation type of Heat transfer.

What is Radiation?

Thermal radiations are called radiant heat. Emission of electromagnetic waves causes thermal radiation to be produced. The energy from the producing body is carried away by these waves. Radiation occurs in a vacuum or through a transparent medium, which might be solid or liquid. The random movement of molecules in matter results in thermal radiation.

Easy explanation of Radiation

As you might already know, Conduction is the best method of heat transfer between solids and Convection is the best method of heat transfer between fluids. As we mentioned, the heat transfer between molecules is how heat moves from a hotter to a colder body. What about places where there are no molecules? Like in space? Have you ever wondered how heat from the sun reaches us all the way from 15 million kilometers? There aren’t even any molecules in the empty space between the sun and us. Radiation is the answer. Radiation is the transfer of heat through regions where there are no molecules. Radiation is an example of electromagnetic energy in action. As you might be knowing,electromagnetic energy travels in waves. Radiation, on the other hand, is heat that travels in waves. Radiation does not require molecules to transfer energy. All objects emit heat, although some emit significantly more than others. The Sun is the most powerful generator of radiation, sending a massive quantity of heat to Earth via electromagnetic waves.

Heat is emitted by light bulbs. If you  Hold your hand a few inches away from a light bulb, you can feel the heat.  Radiation is, in fact, how you can feel heat without touching it, which is an excellent way to remember it. The heat travels across the space until it reaches your hand. That’s radiation in action! Another example of radiation is a fire. You can feel the heat off of a burning flame if you are nearby. You, too, are a good example. Your body produces heat! (This is why a classroom may become hot when there are a lot of people in it.)

Radiation Equation

The wavelengths in the spectrum of the radiation released decrease as the temperature rises, and shorter wavelengths of radiation are emitted. The Stefan-Boltzmann law may be used to calculate thermal radiation:

P = e ∙ σ ∙ A· (Tr⁴ – Tc^{^4})

Where,

P = net power of radiation

A = area of radiation

Tr = radiator temperature

Tc = surrounding temperature

e = emissivity

σ = Stefan’s constant – ​​5.67 × 10−8 watt / m² K⁴