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REFRIGERATION PRINCIPLES OF COLD PRODUCTION

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BASIC KNOWLEDGE

PRINCIPLES OF COLD PRODUCTION

THERMOELECTRIC REFRIGERATION SYSTEM

ABSORPTION REFRIGERATION SYSTEM

The vortex cold generator is an extraordinary refriger-ating machine. Here a cold and a hot air flow is gener-ated from a compressed air flow at room temperature. The compressed air enters a vortex chamber tangen-tially and is moved into fast rotation. At the centre of the vortex a cold air flow forms, while the outer layer of the vortex heats up. The cold air is extracted at the centre and can be used for cooling.

The benefit of this refrigerating machine is that it is of a very simple design, does not have any moving

parts, no toxic working materials and does not require a power supply. The low efficiency is a disadvantage.

ammonia vapour liquid ammonia low concentration ammonia solution high concentration ammonia solution hydrogen hydrogen and ammonia vapour

Col

Cold aair

Compressed air

COMPRESSION REFRIGERATION SYSTEM

COLD GAS REFRIGERATION SYSTEM

The cold gas refrigeration system based on the Stirling principle is used to generate very low temperatures. Areas of application are theliquefaction of air or the cooling of infrared cameras.

The cold gas refrigeration system corresponds to the familiar Stirlingmotor, but the direction of rotation is reversed. This reverses the cycleflow and the power generator becomes a work machine operating as a heat pump.

In the most simple case a compression refrigeration system consists of an evaporator 2 in the room to be cooled 1, a compressor 3, a condenser 4 and an expansion element 5.

The cold gas refrigeration system consists of an operating cylinder 6 and a displacement cylinder 7. In the operating cylinder the operating gas (usually helium) is alternately compressed and expanded. The compressed hot gas discharges its heat in the heat exchanger 4 . During the expansion the gas cools down and absorbs on the cold side 2 of the displacement cylinder heat from the room to be cooled 1. Displacement pistons 8 and operating pistons 6 are moved via a crank drive 5 with offset phases. The recuperator 3 increases the efficiency.

Different types of cold production

Compression refrigeration system

Cold gas refrigeration system (Stirling principle)

Absorption refrigeration system

Thermoelectric cold production (Peltier element)

Vortex cold generator

Here we illustrate

different basic

principles of

cold production.

The compression refrigeration system is used most frequently for cooling. It uses the effect that duringevaporation of a liquid a lot of heat is absorbed. When condensing the vapour this heat is discharged again.

With different pressures during evaporation andcondensing the temperature levels can be adjustedin such a way that heat is transported from the cold tothe hot side.

Because the refrigerant circulates in a closed circuit, this is called the refrigeration cycle. Instead of thepiston compressor shown, screw, scroll, turbo orsteam jet compressors can also be used.

As refrigerant, liquids with a low boiling point, such asfluorinated hydrocarbons (FC), propane, CO2 or NH3,

are used.

VORTEX COLD GENERATOR

Thermoelectric refrigeration systems operate using the Peltier effect. The principle of function corresponds to the reversal of the function of the thermocouple known from temperature measurements. A special semicon-ductor material is used in the Peltier element.

Very low temperatures can be achieved, but the effi-ciency reduces greatly with increasing temperature difference.

Peltier elements are operated with direct current; the direction of the current determines the direction of the heat transport. Therefore, Peltier elements can cool

and heat, are easy to control and do not have any moving parts or liquid fillings.

In an absorption system ammonia (NH3) is used as refrigerant. As in a compression refrigeration system, liquid ammonia evaporates in an evaporator and thereby absorbs heat. The vaporous ammonia is then dissolved in water in an absorber. The ammonia solution is heated releas-ing vaporous ammonia. The ammonia vapour is condensed into liquid ammonia again in a condenser.

To ensure a temperature difference between evaporation and condensa-tion, a pressure difference must be present. This difference is created by a pump for the solution or a so-called auxiliary gas (hydrogen H2). When using the auxiliary gas, a pump can be omitted and the refrigerating machine does not have any moving parts. The supply of the drive energy is purely thermal via a boiler. The boiler can be heated electrically or by gas. The use of waste heat or solar energy is also possible.

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