convection Related Linksphysics

In addition to chemical reactions, physical processes that transfer mass and energy by diffusion or convection occur in gaseous combustion. In the absence of external forces, the rate of component diffusion depends upon the concentration of the constituents, pressure, and temperature changes, and on diffusion coefficients (a measure of the speed of diffusion). The latter are either measured or...

Most agree that plate movement is the result of the convective circulation of Earth’s heated interior, much as envisaged by Arthur Holmes in 1929. The heat source for convection is thought to be the decay of radioactive elements in the mantle. How this convection propels the plates is poorly understood. In the western Pacific Ocean, the subduction of old, dense oceanic crust may be...

Respiratory gases move between the environment and the respiring tissues by two principal mechanisms, convection and diffusion. Convection, or mass flow, is responsible for movement of air from the environment into the lungs and for movement of blood between the lungs and the tissues. Respiratory gases also move by diffusion across tissue barriers such as membranes. Diffusion is the primary...

Apart from some remarks in the above section Compressible flow in gases about the circulation of the atmosphere, no attention has yet been paid to situations in which temperature differences are imposed upon a fluid by contact with hot and cold bodies. This subject will be briefly taken up here.

...the inner chambers of thermos bottles. As far as conduction is concerned, it does not provide any benefits until practically all the air has been removed and free-molecule conduction is occurring. Convection, however, does depend on density, so some degree of insulation is provided by pumping out only some of the air.

...mechanisms involved is pertinent. There are three modes of heat transfer, which can be described as (1) the transfer of heat by conduction in solids or fluids at rest, (2) the transfer of heat by convection in liquids or gases in a state of motion, combining conduction with fluid flow, and (3) the transfer of heat by radiation, which takes place with no material carrier. The flow of heat in...

...convection, thermal radiation (qq.v.), and conduction (see thermal conduction). Conduction involves transfer of energy and entropy between adjacent molecules, usually a slow process. Convection involves movement of a heated fluid, such as air, usually a fairly rapid process. Radiation refers to the transmission of energy as electromagnetic radiation from its emission at a heated...

...Earth’s mantle. Even though a planetary mantle is composed of solid rock, the material there can slowly creep or flow, just as glacial ice does, allowing sweeping convective motions to take place. Convection is a great equalizer of the temperatures of planetary interiors. Similar to heat production within Earth, heat within Venus is thought to be generated by the decay of natural radioactive...

...surface to the atmosphere, it also contributes to the structure of the atmosphere. Three major fluxes are important: the direct transfer of heat from the surface to the atmosphere by conduction and convection (sensible heating), the energy flux to the atmosphere carried by water vapour via evaporation and transpiration from the surface (latent heat energy), and the flux of radiant energy from...

...In addition, the PBL can also be denoted by a thin layer of haze often seen by passengers aboard airplanes during takeoff from airports. During the day, the air within the PBL is thoroughly mixed by convection induced by the heating of Earth’s surface. The thickness of the PBL depends on the intensity of this surface heating and the amount of water evaporated into the air from the biosphere. In...

...the troposphere, which extends from the surface to an altitude of about 10–15 km (6–9 miles), depending on latitude and season. The behaviour of the gases in this layer is controlled by convection. This process involves the turbulent, overturning motions resulting from buoyancy of near-surface air that is warmed by the Sun. Convection maintains a decreasing vertical temperature...

Vertical mixing (convection) occurs in the atmosphere as well as in bodies of water. This process of mixing is also referred to as turbulence. It is a mechanism of heat flux that occurs in the atmosphere in two forms. When the surface is substantially warmer than the overlying air, mixing will spontaneously occur in order to redistribute the heat. This process, referred to as free convection,...

When the rate of temperature decrease with height exceeds the adiabatic lapse rate for a region of the atmosphere, turbulence is generated. This is due to the convective overturn of the air as the warmer lower-level air rises and mixes with the cooler air aloft. In this situation, since the environmental lapse rate is greater than the adiabatic lapse rate, an ascending parcel of air remains...

The region of greatest solar heating at the surface in the humid tropics corresponds to areas of deep cumulonimbus convection. Cumulonimbus clouds routinely form in the tropics where rising parcels of air are warmer than the surrounding ambient atmosphere. They transport water vapour, sensible heat, and Earth’s rotational momentum to the upper portion of the troposphere. As a result of the...

In the Sun’s outermost (though still interior) layers and especially in certain giant stars, energy transport takes place by quite another mechanism: large-scale mass motions of gases—namely, convection. Huge volumes of gas deep within the star become heated, rise to higher layers, and mix with their surroundings, thus releasing great quantities of energy. The extraordinarily complex flow...

...principal heating of air during the day is produced by its contact with a land surface that has been heated by the Sun’s radiation. Heat from the ground is communicated to the air by conduction and convection. Since an inversion will usually control the upper level to which heat is carried by convection, only a shallow layer of air will be heated if the inversion is low and large, and the rise...

...hand, when conditionally unstable air rises it becomes warmer owing to the condensation of water vapour. As the water condenses, heat is released, further warming the air and fueling its rise. This convective action (that is, the circulation of air as a result of heat transfer) produces the huge clouds commonly associated with thunderstorms and tornadoes. Convection can be initiated when the...

...are not generally conducive to tropical cyclone development.A strong vertical coupling of the flow patterns between the upper and lower troposphere is required. This is achieved by large-scale deep convection associated with cumulonimbus clouds.A high humidity level in the middle troposphere from three to six kilometres in height is more conducive to the production of deep cumulonimbus...

...cooling agents customarily employed are air and a liquid (usually water or a solution of water and antifreeze), either alone or in combination. In some cases, direct contact with ambient air (free convection) may be sufficient; in other cases, it may be necessary to employ forced-air convection, created either by a fan or by the natural motion of the hot body. Liquid is typically moved through...

Air also works in conjunction with other systems. When the primary heated medium is steam or hot water, forced air propelled by fans distributes heat by convection (air movement). Even the common steam radiator depends more on convection than on radiation for heat emission.