Stack effect

The chimney effect is a physical effect that causes vertically directed air currents. The chimney effect is due to the natural convection. He will technically be used to remove exhaust gases from furnaces through chimneys.

Principle

Warm air is less dense than cold air, whereby a thermal convection occurs and air exits through the upper opening. Inside is formed under pressure and the external pressure forces air through the lower opening in the chimney, which is also heated. This leads to a self-preservation of the effect.

In most cases, increases in a fireplace warm air upward chimney effects but can occur ( case wind power plant) by " falling " cold air. Through a vertical pipe, the air flow is directed and possibly accelerates, a slight admixture of steam in cooling towers or water shorts the buoyancy increases enormously. Lack the tube, the lift continues, the temperature drops adiabatically. If this reaches the level of the ambient air, ending the buoyancy effect. Even without a chimney pipe this effect can strongly related phenomena occur (see Firestorm, thermal) in nature.

Origin of name

In the stack, also referred to as " fire ", the heated air is discharged through a fire upwards and outwards. With the pull of harmful gases and smoke are deducted and paid to the proximal opening of the hearth of the fireplace dressed down fresh air. Fresh air contains new oxygen, which providing more fuel for the fire. This increases the firing temperature, more air is heated and rises. It comes to a positive feedback.

Hazards

The costs incurred in fire effects flows and pressures and the positive feedback can be dangerous and need to be considered in the planning and construction of buildings. Tunnels and stairways are particularly vulnerable. When fire disaster Kaprun glacier funicular 2 reinforced the chimney effect in the rising tunnel fire and led to a number of deaths.

Benefit

The chimney effect is taken advantage of in addition to the Nutzfeuerung and chimneys also an upwind power plants, where under one roof heated air through a tower rises to the top and this drives turbines as well as in natural draft cooling towers, where the heated cooling water air without any additional aids rises. Moreover, this process takes place on all heated surfaces such as radiators, cooling fins ( motors or electrical components ), house fronts, etc. occurs when the geometric shape and proportions similar to a chimney. Anzündkamine based on this effect to cheer charcoal faster. The effect is sometimes also long been used in home construction, traditional Arab houses around are cooled.

Upside Down chimney effect

A relatively new phenomenon is the " inverted " chimney effect, where the cold air in a shaft drops down, thus based on the same physical principle. This effect is used in case of wind power plants. It also occurs in elevators very high buildings on in warm regions of the world. Warm air enters here into an elevator up and cools down inside, and she drops down and new air moves to be.