Convection transfer is a type of heating in which molecules become lighter or less dense as they warm up and move away from the heat source. Warm air rising when heated by the ground is a common example, as is water rising in a pan when heated from below. Conduction is another type of heat transfer in which heat moves through an object, such as when metal is heated at one end by a flame and becomes hot at the other.
Convection transfer requires a heat source, whether it’s a pan on the stove, the ground, or trees heated by the sun. As the heat source heats up, the molecules closest to it gain energy, causing them to move faster than the molecules around them. Heat transfer would be very slow if nothing else happened, because heat would have to move primarily through conduction. x000D_
Heat travels faster in convection transfer because an increase in energy causes a change in the density of a fluid, which can be a gas or a liquid. The lower density fluid will rise until it cools, at which point it will fall to a lower level. Warm air rises in the atmosphere until it reaches an altitude where clouds form, releasing heat and allowing the air to cool again. Warm water will rise to the surface of a heated pan until it reaches the surface, where heat transfer to the air above the pan occurs and the water cools.
The total fluid volume warms more quickly as the fluid moves through warming and cooling cycles. This is why, on a sunny day, air temperatures can rise quickly due to convection transfer, which causes air movement and warming to occur more quickly than on a cloudy day. It’s worth noting that convection transfer in the air has little impact on wind, which is primarily caused by pressure differences between low and high pressure areas.
Thermals, or rising warm air bubbles, are caused by air convection and can be felt as bumpiness or turbulence by passengers. Glider pilots can use air convection to gain altitude without using a motor by circling in areas of rising air. When rising air meets conditions where water droplets can form as the air cools, convection can produce severe weather. Condensation is the transformation of water vapor into liquid raindrops, which releases heat and causes further heating of the surrounding air. As a result of the convection transfer of warm air and precipitation, an air mass thunderstorm can form. x000D_
Because movement occurs only as a result of changing densities, convection is not a very efficient way to mix fluids. To bring fluids to a constant temperature more quickly, mixing is commonly used in industrial processes. When fluids are mixed, they come into contact with heated surfaces, then quickly move away and are replaced by cooler material. Mixing not only improves heating efficiency, but it also prevents hot spots or areas of extreme heat from damaging chemical reactions.