Learning classroom

Heat Radiation


There are three ways of heat transmission: conduction, convection, and radiation. Among them, when the heat radiation acts, it does not need to be transmitted through any medium, just like electromagnetic waves that transfer thermal energy, just like the sun's thermal energy is transferred to the earth through space like this.


Daily application of heat radiation:

1. Commonly used metal radiator, the surface is usually black, because the black heat radiation effect is better.

2. The surface of the stainless steel kettle is very bright, in order to reduce heat radiation.

3. In order to avoid high temperature, the oil tank is usually painted white, which can reduce heat radiation and avoid overheating of the oil tank.

4. Graphene has good conductivity in the plane direction and has a good thermal radiation coefficient, so it is often used for electronic heat dissipation.


When the charged particles in the atom move, they generate heat. When the thermal energy is converted into electromagnetic radiation, it is called thermal radiation. All substances whose temperature is higher than absolute zero will emit thermal radiation, and the frequency of thermal radiation depends on the object’s temperature.


All objects radiate energy in the form of photons, and the moving direction of these photons is not fixed. When radiant photons from the surface of one object reach the surface of another object, they will emit, reflect, and transmit.

Emissivity (absorption rate) is a measure of the ability of the surface of an object to release energy in the form of heat radiation. Generally speaking, the darker the color of the material, the rougher the surface, the closer the emissivity is to 1.

Reflectivity is the ability of the surface of a material to reflect radiation

Transmittance is the proportion of incident radiation transmitted at a specific wavelength.

Therefore, the reflectance, emissivity, and transmittance of a substance add up to 1. And α+ρ+τ=1.


According to Stefan-Bozmann’s law, we can know

The total radiant power radiated by the surface of the black body per unit area and per unit time



The formula is:

1. Radiation emissivity: M

2.The radiation coefficient of the object:

3. Stefan-Bozeman constant: σ =5.67 × 10-11 kW/m2 K4

4. The absolute temperature of the object: T

It can be seen from the above formula that the radiation emissivity is proportional to the fourth power of the temperature of the object. Therefore, the higher the temperature, the higher the radiation emissivity and the better the radiation effect.



T-Global R&D team

Team introduction –

A team of professional heat flow engineers, with independent and innovative research and development, provides customers with preliminary thermal simulation planning and institutional heat dissipation design consulting. In the face of evolving market trends, they can quickly respond and continue to provide innovative anti-heat solutions.