The radiometric effect is the phenomenon of spontaneous movement of unevenly heated bodies placed in rarefied gases in the direction from the warmer side to the less warmed one. The unevenness of heating is usually carried out by one-sided illumination of the body, which is the name of the effect. The forces that cause the body to move are called radiometric.
Content
- 1 Nature
- 2 Thinning of gas
- 3 See also
- 4 Sources
Nature
Thermal slip plays a role in the formation of radiometric forces β the movement of the surface gas layer toward a hotter part of the body surface and the propagation of this movement to gas layers far from the surface caused by viscosity : since the law of conservation of momentum is fulfilled, the body moves in the opposite direction; this is how dust is collected on cold walls located near central heating batteries.
The second phenomenon, which contributes to the radiometric effect, has a molecular-kinetic origin: gas molecules communicate with a larger momentum from the more heated side of the body than molecules reflecting from the less heated side.
Gas
In dense gases, the phenomenon of radiometric effect does not take place [1] . This is due to the fact that the parietal layer is small, since the molecules travel an extremely short distance from the body to the collision with the next molecule. The mean free path is small. At high pressure, there is also no movement of molecules toward a warmer part of the surface of the body; their movement is absolutely chaotic.
The force caused by the molecular-kinetic nature of the effect is proportional to pressure. It plays a noticeable role in slightly rarefied gases , in which the pressure is relatively small.
The force caused by thermal slip and viscosity is significant in a medium-rarefied gas , since, on the one hand, the thermal slip rate increases with increasing rarefaction of the gas, but, on the other hand, the phenomenon of flow of the βwall layerβ of gas in highly rarefied gases is impossible, since the length the mean free path is large, and the molecules after collisions with the body significantly move away from its surface.
In strongly rarefied gases under the conditions of a small role of thermal slip, the molecular-kinetic side of the radiometric effect also plays the main role.
See also
- Effusion
- Thermal glide
- Crooks Pinwheel
Sources
- β Sivukhin D.V. General course of physics. - M .: Science , 1975 . - T. II. Thermodynamics and molecular physics. - 519 p.