For example, solar radiation reaches the surface of the earth after passing through cold layers of the atmosphere at high altitudes. In contrast to heat transfer by conduction or convection, which occurs in the direction of decreasing temperature, thermal radiation heat transfer can occur between two bodies separated by a medium colder than both bodies. Energy transfer by radiation is fastest (at the speed of light), and it suffers no attenuation in a vacuum.
Thermal radiation does not require any medium for energy transfer. It is generated by the thermal motion of charged particles in matter, and therefore any material with a temperature above absolute zero gives off some radiant energy. The term thermal radiation is frequently used to distinguish this form of electromagnetic radiation from other forms, such as radio waves, x-rays, or gamma rays. Thermal radiation is electromagnetic radiation in the infra-red region of the electromagnetic spectrum, although some of it is in the visible region. It can be expressed by the following equation: Radiation heat transfer rate, q, from a body (e.g., a black body) to its surroundings is proportional to the fourth power of the absolute temperature. Thermal radiation is electromagnetic radiation in the infra-red region of the electromagnetic spectrum, although some are in the visible region.
0 kommentar(er)
