The refrigerating machine vapor compression consists of 4 main organs that are:
- The compressor
- The condenser
- The valve
- Evaporator
The refrigerant describes a closed cycle in four phases through the circuit consisting of the principal organs:
- Compression of the gaseous fluid
- The condensation of the gaseous fluid
- The expansion of the fluid liquid
- Vaporization of liquid fluid (cold production)
Figure 3.0: Basic diagram of a refrigerating machine.
The compressor draws the refrigerant gas (low level of temperature and pressure) from the evaporator, compresses it to a higher level of temperature and pressure and then delivers it to the condenser.
http://www.2ie-edu.org/cours/techniques_frigorifiques/images/vues_compresseur_hermetique.JPG
Figure 3.1: Views of hermetic compressor.
The condenser is a heat exchanger which will enable the evacuation of the heat contained in the gaseous refrigerant from the compressor in the liquefying. This condensation (liquefaction) is obtained by cooling the gas refrigerant at constant pressure by a medium that can be water or air.
This heat removal is done in three steps:
- Superheating of the refrigerant vapor (sensible heat removal - section AB)
- Vapor condensation (latent heat evacuation - main stage - section BC)
- The subcooling of liquid refrigerant (sensible heat removal - section CD)
- The compressor
- The condenser
- The valve
- Evaporator
The refrigerant describes a closed cycle in four phases through the circuit consisting of the principal organs:
- Compression of the gaseous fluid
- The condensation of the gaseous fluid
- The expansion of the fluid liquid
- Vaporization of liquid fluid (cold production)
Figure 3.0: Basic diagram of a refrigerating machine.
The compressor draws the refrigerant gas (low level of temperature and pressure) from the evaporator, compresses it to a higher level of temperature and pressure and then delivers it to the condenser.
http://www.2ie-edu.org/cours/techniques_frigorifiques/images/vues_compresseur_hermetique.JPG
Figure 3.1: Views of hermetic compressor.
The condenser is a heat exchanger which will enable the evacuation of the heat contained in the gaseous refrigerant from the compressor in the liquefying. This condensation (liquefaction) is obtained by cooling the gas refrigerant at constant pressure by a medium that can be water or air.
This heat removal is done in three steps:
- Superheating of the refrigerant vapor (sensible heat removal - section AB)
- Vapor condensation (latent heat evacuation - main stage - section BC)
- The subcooling of liquid refrigerant (sensible heat removal - section CD)
The regulator reduces the pressure of the refrigerant liquid (creation of pressure drop) from the condenser before its introduction into the evaporator in order to allow its evaporation at low temperature in the evaporator.
It also regulates the amount of liquid refrigerant entering the evaporator according to the needs of "cold" (only for thermostatic expansion valves).
For capillary type regulator (capillary tubes), the refrigerant flow arriving in the evaporator is the inside diameter (0.6 to 1.5 mm) and length (from 1.80 to 3.50 m) of the tube and the pressure difference between the condenser and the evaporator.
http://www.2ie-edu.org/cours/techniques_frigorifiques/images/detendeur_capillaire.JPG
Figure 3.3: Pressure capillary.
The evaporator is a heat exchanger wherein the liquid refrigerant of low temperature and pressure will absorb the heat of the medium to be cooled (air or water) at constant pressure thus becoming gas.
This absorption of heat takes place in two stages:
- Evaporation of liquid refrigerant (suction latent heat - main stage - section AB)
- Overheating of the vapors from the evaporation of liquid refrigerant (suction heat sensitive - section BC)
http://www.2ie-edu.org/cours/techniques_frigorifiques/images/evaporateur.JPG
Figure 3.4: Evaporator.
This refrigerant gas is again absorbed by the compressor and the cycle resumes.
3.2 THE COMPRESSORS
3.2.1 Technology compressors
There are two main types of compressors Steam:
- The displacement compressors in which the vapor compression is achieved by reducing the volume inside a compression chamber, this type of compressor is the most common of refrigeration plants.
- Centrifugal compressors also known turbochargers where the compression resulting from the centrifugal force produced by dynamic training using a paddle wheel is a type of compressors for specific applications and used to great powers (refrigeration units high power in HVAC for example).
3.2.2 Positive displacement
There are several types of superchargers and the classification used to distinguish:
- Reciprocating compressors, the best known is the AC compressor piston is the type of compressor most common; vapor compression is achieved by moving one or more pistons in a given capacity (cylinder); we should also mention the axial piston compressors (compressor swash plate) encountered mainly in the field of automotive air conditioning
- Also called rotary compressors vane compressors in which the compression of the vapors is obtained by displacement of a hollow cylindrical body of an eccentric mass acting on a movable blade
- The scroll compressors also known scroll compressors in which the compression of the vapors is obtained by the rotation of a movable scroll a fixed scroll in
- Screw compressors which must be distinguished from the single screw compressors (single rotor) and twin-screw compressors (two rotors)
3.2.3 Centrifugal compressors
A centrifugal compressor is a turbomachine which communicates energy to the refrigerant through one or more wheels rotating in a casing: the kinetic energy resulting from the centrifugal force is then transformed into static pressure in a channel section which increases called volute.
3.2.4 Compressor Engine Association
When we speak of compressor, it implies motorcycle compressor, the compressor being driven by the mechanical part an electric motor.
Depending on the type of connection or association between the two parts are distinguished:
- Hermetic compressors
- Open compressors
- The semi-hermetic compressors or semi open
3.2.4.1 The hermetic
The electric motor and compressor are enclosed in one envelope and unavailable "in principle" to each part in isolation, the assembly is supported generally by springs to prevent vibration transmission.
The compressor draws refrigerant vapor within the envelope and the discharge is performed through a flexible tubing brazed to the casing.
The electric motor is powered by son with terminals sealed.
The tightness of these compressors is provided by fixed joints (passage son and piping).
This type of compressor is used for low power (refrigerators, air conditioners ...) and medium power (liquid chillers, cooling cabinets ...).
3.2.4.2 The open compressors
The electric motor and the compressor are associated by a connecting member which can be a coupling sleeve or one or more belts.
Access to the various components of the compressor as well as those of the engine is possible.
In this type of compressor, the rotational speed is adjustable and modifiable by changing the motor pulley example, however this type requires a rotating seal (rotary joint) to the crossing of the housing by the shaft. It is used for all power.
3.2.4.3 The semi-hermetic compressors or semi open
This is an intermediate type between the previous types. The electric motor and compressor are mounted on a common shaft and on the same frame with the possibility of access to each element, so that these compressors are also called hermetic "accessible." Accessibility is carried out by bolted plates on the frame. This type benefits from the advantages of the open group (access mechanism) and the group sealed (no seal).
They are used for middle powers.
It also regulates the amount of liquid refrigerant entering the evaporator according to the needs of "cold" (only for thermostatic expansion valves).
For capillary type regulator (capillary tubes), the refrigerant flow arriving in the evaporator is the inside diameter (0.6 to 1.5 mm) and length (from 1.80 to 3.50 m) of the tube and the pressure difference between the condenser and the evaporator.
http://www.2ie-edu.org/cours/techniques_frigorifiques/images/detendeur_capillaire.JPG
Figure 3.3: Pressure capillary.
The evaporator is a heat exchanger wherein the liquid refrigerant of low temperature and pressure will absorb the heat of the medium to be cooled (air or water) at constant pressure thus becoming gas.
This absorption of heat takes place in two stages:
- Evaporation of liquid refrigerant (suction latent heat - main stage - section AB)
- Overheating of the vapors from the evaporation of liquid refrigerant (suction heat sensitive - section BC)
http://www.2ie-edu.org/cours/techniques_frigorifiques/images/evaporateur.JPG
Figure 3.4: Evaporator.
This refrigerant gas is again absorbed by the compressor and the cycle resumes.
3.2 THE COMPRESSORS
3.2.1 Technology compressors
There are two main types of compressors Steam:
- The displacement compressors in which the vapor compression is achieved by reducing the volume inside a compression chamber, this type of compressor is the most common of refrigeration plants.
- Centrifugal compressors also known turbochargers where the compression resulting from the centrifugal force produced by dynamic training using a paddle wheel is a type of compressors for specific applications and used to great powers (refrigeration units high power in HVAC for example).
3.2.2 Positive displacement
There are several types of superchargers and the classification used to distinguish:
- Reciprocating compressors, the best known is the AC compressor piston is the type of compressor most common; vapor compression is achieved by moving one or more pistons in a given capacity (cylinder); we should also mention the axial piston compressors (compressor swash plate) encountered mainly in the field of automotive air conditioning
- Also called rotary compressors vane compressors in which the compression of the vapors is obtained by displacement of a hollow cylindrical body of an eccentric mass acting on a movable blade
- The scroll compressors also known scroll compressors in which the compression of the vapors is obtained by the rotation of a movable scroll a fixed scroll in
- Screw compressors which must be distinguished from the single screw compressors (single rotor) and twin-screw compressors (two rotors)
3.2.3 Centrifugal compressors
A centrifugal compressor is a turbomachine which communicates energy to the refrigerant through one or more wheels rotating in a casing: the kinetic energy resulting from the centrifugal force is then transformed into static pressure in a channel section which increases called volute.
3.2.4 Compressor Engine Association
When we speak of compressor, it implies motorcycle compressor, the compressor being driven by the mechanical part an electric motor.
Depending on the type of connection or association between the two parts are distinguished:
- Hermetic compressors
- Open compressors
- The semi-hermetic compressors or semi open
3.2.4.1 The hermetic
The electric motor and compressor are enclosed in one envelope and unavailable "in principle" to each part in isolation, the assembly is supported generally by springs to prevent vibration transmission.
The compressor draws refrigerant vapor within the envelope and the discharge is performed through a flexible tubing brazed to the casing.
The electric motor is powered by son with terminals sealed.
The tightness of these compressors is provided by fixed joints (passage son and piping).
This type of compressor is used for low power (refrigerators, air conditioners ...) and medium power (liquid chillers, cooling cabinets ...).
3.2.4.2 The open compressors
The electric motor and the compressor are associated by a connecting member which can be a coupling sleeve or one or more belts.
Access to the various components of the compressor as well as those of the engine is possible.
In this type of compressor, the rotational speed is adjustable and modifiable by changing the motor pulley example, however this type requires a rotating seal (rotary joint) to the crossing of the housing by the shaft. It is used for all power.
3.2.4.3 The semi-hermetic compressors or semi open
This is an intermediate type between the previous types. The electric motor and compressor are mounted on a common shaft and on the same frame with the possibility of access to each element, so that these compressors are also called hermetic "accessible." Accessibility is carried out by bolted plates on the frame. This type benefits from the advantages of the open group (access mechanism) and the group sealed (no seal).
They are used for middle powers.
