Convection how does it work

The portion of fluid that is less dense then rises, while the denser portion of fluid sinks. The process repeats itself because the less dense fluids cool down as they move away from their heat source, making them sink, while the denser fluids heat up as they near the heat source, making them rise. This creates convection currents. Figure 1. Air over land heats faster than air over water, leading to convection which feels like a cool ocean breeze.

Figure 2. Convection warming a room is quiet and energy efficient. Convection plays a large role in wind patterns and in passive ventilation. The movement of wind across the globe is dependent on various spots where warm air rises and cool air sinks, creating large wind currents that affect weather.

For example, air over land will typically get heated up by the sun during the day, while air over the sea will remain cool. The hot air over land will rise in the atmosphere. As it rises, it also cools down and becomes denser, causing it to sink once more. This concept is illustrated in Figure 1.

These two concepts, that heat causes a decrease in density and that fluids rise and fall according to density, combine to create the heat-transfer phenomenon of convection. Convection is a method of thermal energy transfer where the transfer of heat occurs via fluid motion.

This fluid motion is caused by the difference in density between hotter regions of the fluid and cooler regions. These motions are called convection currents , and the convective movement of fluid continues as long as there is a temperature difference between regions.

This temperature difference is especially stark when there is a source of heat on one side of the fluid, such as a heater near the floor of a room. The warm air at the bottom continuously moves upward, while the cooler air moves downward to be heated and then subsequently also moves upward. The movement of air causes circular currents that will continue unless the air reaches an equilibrium temperature; a glass of water at room temperature will generally not have convective currents, while a glass of water with ice in it will have convective currents.

Convection is often described as a combination of two physical processes: advection and diffusion. Advection is the transport of matter by bulk motion, such as the movement of riverbed silt by the flow of the river. Diffusion is the transport of matter by particle motion from an area of high concentration to an area of low concentration, such as the movement of dye particles spreading through a glass of water.

As convection moves hotter matter higher and cooler matter lower, it does so both by moving the matter in bulk advection and in a particulate way diffusion. Convection cannot, by definition, occur in solids because of the inability to create fluid flow in solid matter the particles cannot move relative to each other, but can only vibrate in place. Heat transfer in solids occurs instead by conduction, or the transfer of vibrational energy from one atom or molecule in a solid crystal to its neighbors.

There are some exceptions to this in soft solids where the particles can move past each other. Keeping convection in mind can help you heat or cool your house more efficiently. Since hot air tends to rise, and cool air tends to sink, it helps to put heaters closer to the floor and air conditioners higher up.

Ceiling fans can usually operate in both directions: either blowing air down from above, or blowing air up from below. Blowing air down is usually helpful in the summer so you feel the convective breeze cooling your skin; pulling air up is helpful in the winter because it helps to push the high-up hot air down and out toward the walls, without blowing directly on you. As water cools, it contracts and becomes more dense like most other substances. However, when it cools to about 4 degrees Celsius, it actually begins to expand slightly.

For example, a saucepan of water over a flame may develop convective currents as the water is heated from below, rises to the surface, and cools. Once cooled enough, the water then sinks back to the bottom of the saucepan where the cycle is repeated, and the convective overturning continues.

Convection is a vital process which helps to redistribute energy away from hotter areas to cooler areas of the Earth, aiding temperature circulation and reducing sharp temperature differences.

Without convection simple tasks such as boiling water in a kettle would be much slower as only the water directly in contact with the heat ring at the bottom of the kettle would be able to be heated, with the water at the top staying cool. Convection is the movement of particles through a substance, transporting their heat energy from hotter areas to cooler areas.

Instead energy is passed from one particle to another upon contact, transferring heat. As a result, conduction in liquids and gases is a much slower process than convection, as particles are free to move and direct contact is reduced. However, conduction is much more effective in solids than convection, as the particles are densely packed, continuously touching one another to allow an efficient transfer of heat.

Additionally, in solids particles fixed and unable to move, stopping the transfer of energy via convection. Convection within the atmosphere can often be observed in our weather.

If conditions allow, this air can continue to rise, cooling as it does so, forming Cumulus clouds. Stronger convection can result in much larger clouds developing as the air rises higher before it is cooled, sometimes producing Cumulonimbus clouds and even thunderstorms.