Radiator (engine cooling)

A radiator is a body that emits heat primarily by thermal radiation. Radiators have a large surface with high emissivity and usually consist of a good heat conducting metal.


Radiators are heat exchangers ( heat exchanger). Through the radiator, a medium (usually in the infrared range ) radiate heat. The hotter, the greater the amount of heat that can be radiated per unit of time and area. Duplicate absolute temperature ( in Kelvin = causes 16 times the energy radiation (Stefan - Boltzmann law ). When calculating the net quantity of heat transferred, the radiation should be taken into account on the radiator ( exchange radiation ).

As high as possible within the range of maximum emission emissivity improved heat dissipation. The range of the maximum emission is shifted, depending on the absolute temperature of the mid-infrared at room temperature up to the near infrared at a temperature of more than 100 to 1000 ° C. The emissivity is determined by the surface material and texture. A rough or jagged surface increases the emissivity. Oxide layers on metal and ceramic has a very high emissivity in the Middle infrared. In the near infrared, it is difficult to produce surfaces with a high emissivity.

Combination with other heat transfer mechanisms

The proportion of heat radiation to the total heat release, for example, for hot water heating due to the low absolute temperature insignificant so that the labels or convector heating or cooling body would be more accurate. The term radiator for radiator varies regionally common.

The emissivity but can also be improved at low temperatures by a high emissivity. Decisive here is the emissivity in mid-infrared; he is at a lacquer coating any color close to 100 %.

Stark can improve the heat transfer through a large surface favorable form for free convection or even through arranged on the radiator fan. You should dissipate immediately surrounding, warmed by heat transfer air. This forced convection affects greatly increasing the heat dissipation and reduces required for a given heat output temperature difference.

Examples of radiators

Characteristic is the ribbed size makes large surfaces are achieved. Aluminum heat sink plate or extruded aluminum profiles are the usual heatsink of power semiconductors. The cooling fins of an air cooled engine engine block provide basically also represents a radiator

In electron tubes grid and anode must be cooled, you often have blackened cooling fins or ribs. In radiation- cooled tubes with glass piston eliminates convection and conduction, since the space between electrodes and piston is empty. In other designs, the metal portion of the anode to project outward, where it is air-or water-cooled.

Radiators of computer cooling, chillers, air conditioners or oil transformers often have fans, but are an extra maintenance and reliability problem.

Spacecraft can be cooled exclusively by radiation. They have this on the outer skin, depending on the sunlight to be closed or open blinds. See temperature control in space.

The heat from the interior of devices is often done with a liquid cycle or a heat pipe to a radiator.