Convection (from lat. Convectiō - “transfer”) is a type of heat transfer in which internal energy is transmitted by jets and streams. There is a so-called natural convection , which occurs in a substance spontaneously when it is unevenly heated in a gravitational field. With this convection, the lower layers of the substance cool, become lighter and float, and the upper layers, on the contrary, cool, become heavier and fall down, after which the process is repeated again and again. Under certain conditions, the mixing process self-organizes into the structure of individual vortices and a more or less regular lattice of convection cells is obtained.
| Flow liquids and gas | |
| Creeping current | |
| Laminar flow | |
| Potential course | |
| Separation of the current | |
| Vortex | |
| Instability | |
| Turbulence | |
| Convection | |
| Shock wave | |
| Supersonic flow | |
Distinguish between laminar and turbulent convection.
Many atmospheric phenomena, including the formation of clouds , are required for natural convection. Thanks to the same phenomenon, tectonic plates move . Convection is responsible for the appearance of granules in the sun .
In forced (forced) convection, the movement of the substance is due to the action of external forces (pump, fan blades, etc.). It is used when natural convection is not effective enough.
Convection is also called the transfer of heat, mass, or electric charges to a moving medium.
Content
Types of convection
Natural - heating / cooling of liquid, air in the room, water in the ocean, steady winds (trade winds, monsoons).
Forced - mixing of liquid or gas (mixer, spoon, pump, fan).
Types of convection due to occurrence
- Thermogravitational convection - ordinary, under the influence of the temperature difference in the gravitational field, due to the force of Archimedes
- Benard cells
- Thermocapillary convection - under the influence of surface tension
- Concentration convection - under the influence of a concentration gradient of solute ( osmosis , see also Marangoni effect )
- Thermomagnetic convection - in magnetic fluids under the influence of a magnetic field in a gravitational field
- Granular convection - in loose inhomogeneous environments
- Thermostress convection - under the influence of temperature stresses
- Thermodynamic convection - the transfer of heat by the flow of matter arising in the field of gravity due to uneven heating of gaseous, flowing or bulk solids.
Mathematical Description
The most popular model for describing convection in liquids and gases is the Boussinesq approximation
See also
- Convection Condition
- Convection zone
- Thermodynamics of the atmosphere
Other methods of heat transfer
- Heat transfer
- Thermal conductivity
- Thermal radiation
- Advection
Links
- Convection (video tutorial, 8th grade program)
- Convection in liquid (video demonstration of experience)
Literature
- Ostroumov G.A. Free thermal convection in the conditions of an internal problem. Moscow - Leningrad. Gostekhizdat. - 1952.
- Landau L.D., Lifshits E.M. Course in Theoretical Physics. T. 6. Hydrodynamics. — M.: Nauka. — 1988. — 736 pp. — (§ 56 Free convection).
- Gershuni G.Z., Zhukhovitsky E.M. Stability of convective flows. - M.: Nauka. - 1989.
- Gershuni G.Z., Zhukhovitsky E.M. Convective stability of an incompressible fluid.- M.: Nauka. - 1972.
- Kriegel AM On the applicability of the approximation of free convection to atmospheric turbulence // Bulletin of the Leningrad State. University. — Ser. 7. — 1991. — Issue 2 (14). — S.107-110.
- Kriegel A. M. Issues of thermodynamics of turbulent convection. // Journal of Technical Physics. — 2016.— 86. — Issue 11. — S.136-139.