What is Radiation Heat Transfer?
The process of transferring heat through Electromagnetic Radiation, which is generated by the thermal motion of particles in matter, is known as thermal radiation. This particular electromagnetic radiation is found in the infrared area of the spectrum, which is invisible to most bodies on Earth. Thermal Radiation is emitted by every particle having a temperature greater than absolute zero. The mobility of particles inside the body is what causes thermal radiation. This type of motion is completely stopped at absolute zero, which is why a body at absolute zero does not admit any radiation whereas anything above absolute zero does.
Radiation heat loss is the difference between the energy state that existed before and the energy that is radiated out after it. Thermal radiation is largely responsible for the glowing quality of hot objects, with iron being referred to as "red hot" since most of the thermal energy emitted by the body at that temperature falls in the red band of the spectrum. It will begin to emit a distinct colour at even higher temperatures. It's an interesting story about how heat radiation was discovered. William Herschel, an English astronomer, discovered it. When he moved a thermometer from one aperture of a prism spectrum to another.
Properties of Radiation Heat Transfer
Radiation is the energy emitted by matter in the form of electromagnetic waves as a result of changes in the electronic configurations of atoms and molecules. Thermal radiation or Radiation heat transfer is defined by four key characteristics.
- At any temperature, a body's thermal radiation emits a wide variety of frequencies. Planck's equation of black-body radiation gives the frequency distribution for an idealized emitter.
- As the temperature of the emitter rises, the primary frequency (or colour) range of the emitted radiation moves to higher frequencies. A red hot item, for example, radiates primarily in the visible band's long wavelengths (red and orange). It begins to produce detectable amounts of green and blue light as it heats up further, and the dispersion of frequencies over the visible range causes it to seem white to the human eye; it is white-hot. Even at a white-hot temperature of 2000 K, 99 per cent of the radiation's energy is still infrared. This is determined by Wien's displacement law.
- As the temperature rises, the total amount of radiation of all frequencies increases sharply; it rises as T4, where T is the absolute temperature of the body.
- Reciprocity describes how the rate of electromagnetic radiation released at a particular frequency is related to the quantity of absorption experienced by the source. As a result, a surface that absorbs more red light emits more red light when heated.
A Black Body Thermal Radiator's Subjective Color
William Herschel discovered that the temperature changed. The greatest temperature recorded fell below the visible light spectrum's red band. As a result, the term "infrared" was coined. Infrared waves, on the other hand, should not be mistaken for heat waves. The subjective colours in relation to temperature are as follows:
faint red glow
bright red, slightly orange
white (When viewed from afar through the atmosphere, it appears yellowish.)
The entire amount of radiation (all wavelength range radiations) emitted by a body per unit area and time is known as the emissive power. The emissive power of a black body, according to Stefan- Boltzmann, is proportional to absolute temperature to the fourth power.
Eb = σAT4
Where σ = Stefan-Boltzmann constant