What is Radiation?
Radiation is defined as the emission of electromagnetic waves, especially high energy particles from a body. Radiation is even emitted by all the smart phones we used previously and also now a days. We can find radiation at any place on the earth. Even in places where the connectivity is unavailable, sun’s rays are responsible for radiation.
What is Heat Transfer?
Heat Transfer is the transfer of thermal energy from one place to another place or from one body to another body. The heat transfer may be of three types. They are Conduction, Convection and Radiation. Other than the three types of heat transfer mentioned above, there are no other ways.
What is Radiation Heat Transfer?
The heat transfer caused because of the electromagnetic waves is known as Radiation Heat Transfer. Radiation Heat Transfer is also known as Black Body Radiation.
Each and every body emits radiation ( Radiant Energy ) as photons which are not constant at a place. They emit radiation because of the thermal agitation of the existing molecules in a material. They continuously move in random motion from one place to another place. Let us say, electromagnetic waves are passed through a body. The body may work on two functions, i.e., transmittance and absorbance. The body may transfer the radiation or absorb the radiation. Sometimes, the radiation may also be reflected back.
A Black body is defined as a body that absorbs every amount of radiation that falls on its surface. Until now, we have known only partial black bodies or just not a black body. But we have never come across a complete black body that absorbs all the radiation falling on its surface. These bodies do not reflect light but absorbs each and every photon present in the light. So these bodies seem to be black in color as they do not reflect any amount of light. This is also the reason for its name – Black Body. The black bodies emit radiation when they are heated to a certain degree of temperature.
When the heat emission is zero, the amount of radiation emitted by its surfaces in also zero. Even though the heat emission increases, the radiation from the surfaces may not effect until a certain amount of emission is achieved. But once the radiation starts coming, it is directly proportional to temperature of emission surfaces.
Even the sun is considered as a black body. So, if the sun continuously emits radiation, the surface of the earth absorbs some amount of radiation, transmits some amount of radiation and reflects some amount of radiation.
There are even grey bodies which have a property of slight or partial reflectance, partial absorbance and partial transmittance. Grey body is a hypothetical source.
Black Body Examples –
- Super Black made out of a Nickel – Phosphorous alloy.
- Acktar Magic Black made out of Vacuum Deposition Technology.
- Sun and all the stars
- Light bulbs
- Heat Lamps
- Electric Heaters and Radiators.
- Electric Stoves
- 8 Night Vision Glasses
- A Candle Flame
This is all about Radiation Heat Transfer.