Convection

Convection is heat transfer by the bulk movement of a fluid, such as a liquid or gas. It occurs through fluid motion driven by temperature differences or imposed flow.

Buoyancy: The upward force on an object immersed in a fluid, caused by pressure increasing with depth. Temperature differences change fluid density, creating buoyant motion that drives natural convection.
Heat transfer: The movement of thermal energy from hotter regions to colder regions. Convection is one of the principal modes by which heat moves.
Atmospheric convection: Vertical air motion driven by buoyancy in Earth's atmosphere. Rising warm air and sinking cooler air organize clouds, storms, and vertical heat transport.
Rayleigh–Bénard convection: A pattern of fluid circulation that forms when a horizontal fluid layer is heated from below and cooled from above. It is the classic laboratory case for the transition from conduction to buoyancy-driven convection.
Advection: The transport of a substance or property by the bulk motion of a fluid. Advection describes transport by flow broadly; convection commonly emphasizes heat transfer and may include buoyancy-driven flow.
Thermal boundary layer: A thin region near a surface where fluid temperature changes rapidly between the surface and the surrounding flow. Much of the heat exchange in convection occurs across this thin layer.
Conduction: Heat transfer through microscopic interactions or particle motion without bulk movement of matter. Conduction transfers heat without the fluid circulation that defines convection.
Ocean circulation: The large-scale movement of seawater driven by winds, tides, and differences in density. Convection helps redistribute heat and salt through the ocean's interior.
Benard cells: Polygonal convection cells that form in a thin fluid layer heated from below. Their visible cellular pattern makes convection's organized motion easy to observe.
Diffusion: The net spreading of particles or energy from regions of higher concentration toward lower concentration through random motion. Diffusion spreads heat without the organized bulk flow central to convection.

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