Thermal Radiation Heat Transfer

Thermal Radiation

Heat is a very peculiar form of energy. It assists us in staying warm, makes hot and tasty food, but when it is applied in daily life, it far exceeds the domestic uses mentioned here. By understanding the properties of heat, we can find the key to many branches of science. Thermodynamics is a vast field which deals only with the flow of heat through a system. Even nuclear energy which uses the heat, developed by the atom to create electricity. So it is crystal clear that heat is significant to us. This makes it much vitally essential for us to take a closer look at heat. Thermal Radiation and heat transfer are very important for us to understand the heat energy. Its transmission will help us to understand the characteristics of heat transfer and thermal Radiation.

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What is Heat Transfer?

Heat transfer is defined as the process of transfer of heat from a high-temperature state of the body to the low-temperature state of the body. By following the modes of heat transfer, we can say that thermal Radiation can be of three types:

Conduction: It can be defined to be the heat transfer between two solids.

Convection: It can be defined to be the heat transfer between solid and liquid.

Radiation: It can be defined to be heat transfer when there are no media involved.


What is Thermal Radiation?

Thermal Radiation is the process of transfer of heat by the help of the Electromagnetic Radiation, which is generated by the thermal motion of particles in matter. For the maximum bodies on Earth, this particular electromagnetic Radiation lies in the invisible part of the spectrum, which is known as the Infrared region. Each and every particle with a temperature above is the absolute zero, which emits Thermal Radiation. Thermal Radiation is generally caused by the motion of the particles inside the body. At the absolute zero, this type of motion is wholly stopped, which is the reason why a body at absolute zero does not allow any radiation and everything above absolute zero does. The difference between the state of energy which was there before and the energy which is radiated out after it is called radiation heat loss. Thermal Radiation is very much responsible for the glowing nature of hot objects where iron is often termed as being red hot because at that temperature most of the thermal energy emitted by the body falls in the red band of the spectrum. At very even higher temperatures, it will start emitting a different colour. The invention of heat radiation is a fascinating one. It was invented by the English Astronomer, William Herschel. He noticed that when a thermometer is moved from one aperture of a prism spectrum to another, this will result in a temperature change. The highest temperature which was observed was below the red band of the visible light spectrum. Therefore, the name Infrared. Infrared waves, though, should not be allowed to be confused with Heatwaves. Hence, all forms of electromagnetic radiation transfer energy take from place to place; they could all be coined the term as Heat Waves.


Solved Examples

How is Radiation Different from Other Two Modes?

Unlike the processes of Conduction and Convection, Thermal Radiation does not require any medium to transfer heat. The heat which the Earth receives from the sun is by the process of Radiation. This is because the Radiation can be provided through electromagnetic waves, and they do not require a medium for transmission. Thermal Radiation has another fascinating property. It has been discovered that darker bodies can absorb and have to emit heat radiation better than bodies which are constituted with lighter colours. 


Did You Know?

Autoclaving is a very general method of heat sterilisation in which steam is applied under pressure at a temperature of 121 °C for 15 minutes. This technique applies only to items which are not at all heat sensitive or would have their properties to change during the process. The procedures of Sterilisation or filtration can also be achieved for the case of liquids and gases which are heat generally sensitive, which is used to an appropriate size filter for the contaminant, which is to be excluded. This is a very general method of using heat transfer which is used to isolate viruses. 

FAQ (Frequently Asked Questions)

1. Why Do People Wear Lighter Clothes in Summer and Dark Clothes in Winter?

Answer: Black colour especially is high-speed at both absorption and emission characteristics of heat than that of white. For human beings, thermal emissivity does not depend on the colour of the skin. Skin is a perfect absorber and emitter of Thermal Radiation. If we saw a human and passed him/her through infrared waves, we would all appear to be black coloured. We tend to lose half of our energy through the Radiation even when the surrounding atmosphere is not very much colder than our body. This is the reason why people have a tendency to wear white colours in summers and darker colours in winters.

2. What is Therapeutic Heat Transfer?

Answer: Therapeutic heat transfer is the process that occurs by one or more combinations of mechanisms like Radiation, conduction, conversion, and evaporation. Radiation is the procedure of transfer of heat through thermal Radiation at the surface. Conduction is the particular heat exchange which is done through direct contact. Convection has features which transfer thermal energy by the movement in a fluid medium, although the therapeutic energy exchange can still take place through conduction. Conversion takes place when a different type of energy is changed to heat energy. Evaporation leads to the loss of heat when a liquid on a surface moves to a phase transition into a gas. These mechanisms are an essential part of thermal Radiation which has many uses.