Refrigerator compressor, operating principle and classification

The refrigeration unit can be divided into three large parts. These are such as evaporator, condenser and compressor. All three parts are linked. The system of work is closed in nature. The main purpose of the compressor is to provide the required temperature in the refrigerator chambers. A refrigerant is used as a gas.

Principle of operation and types

The compressor in the refrigerator is designed to maintain the cold, or rather, to circulate the coolant through the capillary tube system and the radiator grill of the refrigerator, condenser.

In order to understand what role the compressor plays in the refrigerator, you need to imagine how the freezing process takes place.

The compressor, which is a motor, pumps out refrigerant vapors from the evaporator, and then directs them to the condenser. In it, the vapors are cooled and the condensation process begins. Being in a liquefied state, the refrigerant enters the evaporator through pipes and a filter intended for dehumidification. There, due to the pressure difference, the substance boils, the energy for boiling comes from the evaporator, and the air in the chamber is cooled. The refrigerant again changes its phase state, turns into gas. The process is repeated again.

Compressor units are divided into types:

• dynamic;
• piston;
• rotary.

Each type has its own advantages and disadvantages. Dynamic fans use in their work, with their help, the refrigerant is pumped. The piston is based on the same operation principle as in single-cylinder internal combustion engines, it has an engine and a shaft. The rotary one contains a rolling rotor located in the housing cylinder eccentrically.

Dynamic compressors

They are divided into two classes according to the type of fans: axial and centrifugal. The first use the fact that the compression of the refrigerant occurs after the change in its speed between the blades of the rotor and the guide device. In this case, the movement of the refrigerant is carried out in the direction of the rotor axis. In the second type, a vacuum occurs on the supply side, gas is supplied to the impeller blades. When it rotates, the coolant is thrown, under the influence of centrifugal force, to the outer radius. At the exit from the wheel, the gas is directed to the diffuser, where its speed decreases and the pressure increases.

Their classification is carried out according to the following criteria:

• By final pressure. The pressure created by the gas flow.
• By the number of compression stages. Single-stage and multi-stage.
• By the type of drive. Turbine or electric.

Dynamic compressors are characterized by uncomplicated design, durability and ease of use. The device has small dimensions and weight. The main disadvantage is the low efficiency, which is especially evident at low productivity and high pumping pressures. In such a design, it is impossible to obtain a high compression ratio, and therefore create a high pressure.

Reciprocating compressors

Compressors of this type are reciprocating. Compression is created by reducing the volume of the cooling gas when the piston moves in the cylinder. They are distinguished by the following features:

• Using a crank drive or linear mechanism.
• By the location of the cylinders. They can be made in vertical, horizontal or angular design (rectangular).
• By the number of compression stages. Available in one-, two- and multi-stage, depending on the need to limit the temperature of the discharge gas.

The motor drives the crankshaft in the middle of the compressor at start-up. Carrying out reciprocating rotations, the piston with its movements pumps out the gas, distilling it from the evaporator into the condenser. Using the suction valve, the refrigerant enters the chamber during discharge and is discharged back during discharge, during the return stroke, forming an increased gas pressure. Thus, a non-straight piston is used, consisting of two valves, supply and discharge.

Another design is used, it is more economical and simpler. It is based on an inverter pulse shaping circuit. Such a product is a rod with a piston at the end located inside the coil. When an alternating current is applied, a magnetic field arises, and the system under its action starts to move.

Modern devices of this type do not use lubricant, the pistons are sealed with piston rings.

Reciprocating compressors are one of the first to be used in refrigerators. They are distinguished by good reliability, they can operate in a wide voltage range. Lack of noise and vibration during starting / stopping the engine.

Rotary compressors

A system is used, consisting of two rotors, a master and a slave. Rotating towards each other, and touching along the entire length, gas pressure is created. The device is made in such a way that there are no gaps between the rotors and the body, the portions of gas formed by the intake chambers diverge in different directions and easily gripped by two shafts. The refrigerant, getting into the chambers with a decrease in their volume, is compressed, and then redirected, through a special hole of small diameter, into the condenser. The peculiarity is that one of the rotors takes up most of the portion, in a ratio of 4 to 6.

The advantage of this design is high efficiency, and due to the fact that the rotational speed of the rotors does not depend on pressure, a steady state is ensured. Vibration and noise are virtually absent. Since the rotors touch without gaps, and there is oil between them, there is no friction and a high rotation speed is not needed. This results in a low power consumption value. The oil, due to surface tension, forms a plug between the working parts and the body, which leads to an increase in pressure.

The use of two rotors on one shaft is justified by the increased reliability and efficiency. Remaining unchanged in the principle of operation, the design itself can have various variations. The arrangement of two additional plates on the rotor made it possible to obtain more pressure, but led to an increase in friction and a complication of the design.

Some models use an oscillating rotor. This is due to the fact that recently a new type of refrigerant has been used. Previously, the cooling gas, due to the content of chlorine in its composition, formed an additional protective ferro-chloride film. This film not only reduced friction, but also reduced the possibility of corrosion. At the same time, the use of new refrigerants led to a pressure loss due to losses during overflow of gas between the rotor and the cylinder of the housing, as well as the cylinder and the end face of the plate. To reduce losses due to friction and overflow, the plate with the rotor is made in one piece.

Comparison of linear and inverter types

Compressors are divided into linear and inverter based on operating mode. Currently, more and more refrigeration units are manufactured with an inverter compressor. Linear devices operate in a cyclic on and off mode. After the refrigerator is connected to the network, a sensor located in its chamber determines the temperature by comparing it with the set one. The compressor starts up and the cooling process begins. After reaching the required value, the compressor turns off, and the sensor continues to monitor the temperature. As soon as it rises and goes out of the set range, the compressor starts up again.

Inverter devices work on a different principle. After turning on the unit and reaching the desired temperature in the chamber, it does not turn off, but reduces the speed, maintaining the temperature regime constant. The inverter compressor does not have a rotating rotor motor. The compressor does its work by itself: the piston makes movements under the influence of an electromagnetic field.

The main disadvantage of linear compressors increased load on the electrical network, which leads to voltage surges and increased energy consumption, compared to inverter units. The noise from the inverter compressor is minimal, however, it is quite susceptible to the quality of the mains supply. Therefore, in case of a poor electrical line, it is recommended to use it in conjunction with a voltage stabilizer. Linear devices are cheaper for the price, but one should not forget about power consumption.

Two-compressor refrigerator

In modern models, two compressor units began to be installed at once. One compressor is used in both single-chamber and double-chamber units, while two are used only in double-chamber units.

Model manufacturers report that the use of two devices will reduce energy consumption, due to separate temperature control in both the freezer and the main one. In addition, the service life of such models is higher, since each compressor starts only when it is necessary to reduce the temperature in its chamber.

If the compressor fails, you will have to purchase a new one. In this case, it will be necessary to look for the same type. Its main parameters are power, type of refrigerant and the presence of a start relay.