Air cooling

With air cooling the surface of the heat-generating objects is cooled by air flowing past it. In internal combustion engines, electric motors or electronic components of the power electronics, the overheating and destruction of components is to be avoided; in refrigeration and air-conditioning systems below the condensing temperature of the refrigerant is essential for the function.

General

The necessary cooling air to the air movement may be effected either by convection blower for vehicles or by the wind. The object to be cooled is free or is circled channeled. Often the object to be cooled is also provided with cooling fins or a heat sink as a heat exchanger, which, through a greater surface area greater heat dissipation.

Air-cooled engines

A fundamental disadvantage of air cooling over water cooling is that the heat transfer coefficient between air and a solid by a factor of 50 to 100 is lower than the heat transfer coefficient between water and solids. The cooling air, therefore, requires a larger contact area between the two media (which may be optionally enhanced by the cooling fins ), and higher flow rates (which can be optionally secured by a cooling fan ) and the water cooling.

Combustion engines

Main article: cooling ( internal combustion engine)

In contrast to water-cooled engines air cooled engine when the temperature does not burst due to freezing of the cooling water and the cooling liquid and not boil over at too high temperatures below freezing, because no coolant or no coolant is present. For trucks, the efficiency of air cooling is superior to the cooling water, which is why trucks with air-cooled engines have lower fuel consumption than trucks with water-cooled engines of the same power.

As a powerful cooling fan is required for cars with air-cooled engines, which requires more power than the water pump of a cooling system, the overall efficiency of air-cooled engines in passenger cars is worse than that of water-cooled engines. Also, air-cooled internal combustion engines are generally quite loud and a powerful interior heating is difficult to achieve. Moreover the operating temperature, and thus the performance and the consumption of an air- cooled engine depends strongly from the current outside temperature, so that many air-cooled vehicles still have an oil cooler with a thermostat. Also occur on air cooling to higher temperatures than water cooling, whereby compliance with modern emissions regulations is difficult. Air-cooled engines are therefore used less and less in motor vehicles.

Cars such as the Porsche 911, the Volkswagen Beetle, the Trabant and the Citroën 2CV, but also trucks from Magirus -Deutz, Robur and Tatra have been equipped with air-cooled engines. On motorcycles you will find air-cooled engines are still quite common. Companies like Harley- Davidson, Buell, Ducati, Moto Guzzi and BMW have many models with air cooling in the current program. Further applications of the air-cooled engine in propeller airplanes and RC cars with internal combustion engines.

Air-cooled engine under the " alligator hood " of a Magirus- Deutz round Hauber

Air-cooled engine from VW in cross-section

Air-cooled Porsche engine in the Type 550 Spyder

Air-cooled V-2 engine of a Buell XB model

Air-cooled four-cylinder inline engine of a Yamaha XJR 1300

Air cooling with personal computers

In relation to their size goes - especially in processors from the Intel 486/66 class - with the technology commercially economically available to a large heat evolution associated. Powerful micro- chips, such as those used in modern computers, generate significant heat loss, which is mainly dissipated by air cooling. The purpose is not to exceed the permissible temperature of the crystal present in the semiconductor processor. Exceeding means destruction of the transistor semiconductor crystals begin to melt through or by doping the alloy which can cause a short circuit on the chip.

Since the total input power is converted almost entirely into heat, an attempt was made to reduce the power dissipation by reducing the electrical voltage of solid heat-generating components. Furthermore, in current processors parts of the computational work can be reduced when not in use in the clock frequency or shut down completely. Nevertheless, the natural heat dissipation was no longer enough by radiation and convection, so that the thermally active surfaces were first cooled by the use of heat sinks and then - because still not enough - was the possible heat dissipation through the use of electrically powered fans enlarged ( cf. processor cooler ). The most chilled element in PCs, depending on the composition of components in the computer, either the CPU, followed closely by the GPU of the graphics card, or the first graphics processor followed by the CPU. Alternatively, let cool in the meantime almost all components with water cooling.

The most effective cooling can be achieved by evaporation of suitable liquids; work out all the chillers according to this principle.

Other applications

• HiFi amplifier are air-cooled normally.
• For cooling the chips in the machining of hygroscopic (moisture attracting) plastic happens to air, the usual cooling lubricants could dissolve the material or swell.