Refrigeration

Refrigeration is the process in which a system or subject to heat or thermal energy is removed. Linguistically, therefore, heat dissipation is used as the correct designation for cooling.

In the HVAC Cooling describe all the measures that serve to dissipate the heat losses incurred technical components to the environment. Desired cooling is used in order to protect it from overheating, to achieve certain temperature dependent characteristics, and to obtain, or for preservation purposes in biological material.

Unwanted heat loss can be compensated by insulation or heating, where one speaks in animals of hypothermia or frostbite.

• 4.1 functionalities
• 4.2 Areas of application
• 4.3 Examples
• 4.4 See also

Fundamentals of Thermodynamics

The removal of heat proceeds for solids and liquids by heat transfer corresponding to a temperature gradient. The principal processes are thermal conduction and thermal radiation, also limited convection. The most effective way with the highest power density is evaporative cooling.

Since all of these processes occur spontaneously, and thus result in accordance with the basic laws of thermodynamics, temperature compensation, an artificially desired cooling an object against a temperature gradient can be done only with great expenditure of energy. Overall, this will, however, always with an increase in the total entropy and thus usually a conversion result of a higher order forms of energy into thermal energy. A cooling in the sense of a reduction of the thermal energy of an isolated system is therefore not possible, which, in practice, for example, expresses the fact that even refrigerators ultimately increase the temperature ( the environment), not lower, though this may also be the case locally.

The various processes of heat transfer are each characteristic of certain situations. Thus, the convection plays for solids not matter here dominate heat conduction and heat radiation. This is evident for example in the broadcast of the earth's surface. The decisive factors are given by coefficient of thermal conductivity, heat transfer coefficient and heat capacity.

In liquids, the heat conduction and heat radiation also plays a role, but added the convection as an essential process of temperature equalization.

This, however, dominates in gases, which cool generally very bad about processes of heat conduction. However, they are subject to various gas laws, whereby especially the adiabatic cooling and the Joule- Thomson effect plays a major role. Of particular importance have this in the atmosphere when air parcels cool down or warm up for vertical movements corresponding to the atmospheric temperature gradient. About condensation and Resublimationsprozesse the cooling associated with this is a key factor in the precipitation and the weather in general.

Cooling capacity

The cooling capacity is similar to the electrical power to specify how much heat energy per unit time is removed. Accordingly, the heat flux is the per unit area flowing through heat output.

Cooling options / modes

For oil -filled equipment, a distinction is made ​​between the following types of cooling:

If it can be switched between these variants cooling by fans or pumps on and off, are you speaking of modes. The cooling performance changed as a result. The switch should be automated in order to adjust the cooling capacity to the respective quantity of heat can.

Benchmarking

The following table shows an example of tubes for transmitting different types of cooling the structure of the anode, and the maximum specific load.

By far the largest capacity arises in the evaporative cooling. This much energy is used during evaporation of the liquid cooling medium to in this way a high power density of the refrigerant to (mostly water) exits. The principle of evaporative cooling is used, for example, the water-cooled vehicle engine to be very effective to limit the temperature.

Technical application

Cooling systems can be divided according to the heat transfer medium used. The most common types of cooling are:

• Liquid cooling / water cooling and
• Air cooling or water cooling material for large generators.

Less well-known

• Oil cooling, eg in internal combustion engine and hydraulic systems ( hydraulic drive )
• Sodium-cooled nuclear power plants or
• Cooling by Peltier elements such as for use in coolers for camping area, rare for cooling processors. Their disadvantages, such as the relatively poor efficiency is taken into account in applications where the benefits outweigh such as in measuring instruments for gases or liquids, which require constant temperatures. This can be both cooled and heated with Peltier.

Basic research at low temperatures with liquid nitrogen (about -196 ° C ) and cooled to the temperature range of about 1 to 4 Kelvin with liquid helium (usually in a cryostat, see also at low temperature physics ). The helium isotope 3He allows temperatures down to 1 mK, see in 3He - 4He mixture cooling. For even lower temperatures one can use the Magnetic cooling, laser cooling and evaporative cooling.

Modes of operation

Cooling is usually based on the transfer of heat from the body to be cooled to the cooling substance ( gas or liquid) and transport (heat flow ).

In some applications with limited space ( inside a computer or hi-fi amplifier ) for transporting heat pipes are used.

There is a special coolant for most motors.

Areas of application

Cooling systems are used in many technical devices that heat up, used. Usually, however, a passive cooling system, that is, the discharge of heat via the cooling body to the surrounding air, used.

The best known example is the refrigerator to preserve food. In motor vehicles, water cooling is usually used in computers are primarily air cooling is used. Another major area of ​​application is for example the air conditioning.

Examples

• Cooling systems of power plants and chemical processes
• Cooling in air conditioning technology
• Oil and charge air cooler turbo diesel engine
• Exhaust gas cooling in EGR systems ( to reduce emissions (NOx ) )
• Water cooling system of a car engine
• Water cooling a processor
• Air cooling a processor
• For experimental purposes, to bring substances into the vicinity of 0 Kelvin brand
• Ship cooling systems
• Dry cooling
• Cooling of the exhaust gases from ships or tanks to on enemy infrared ( thermal imaging camera ) to be as light / late visible ( eg ship here )