How a refrigerator works: the structure and operating principle of the main types of refrigerators. The principle of operation of the refrigeration unit

It is impossible to imagine the home comfort of a modern person without a refrigerator. It is designed for long-term storage of food. According to scientists, each family member opens the door up to 40 times a day. We look inside without even thinking about how our refrigerator works.

In our article we will take a detailed look at the design and operating principle of various refrigerators.

How does a refrigerator work?

Any modern refrigerator consists of the following main units:

1. Engine.
2. Capacitor.
3. Evaporator.
4. Capillary tube.
5. Drying filter.
6. Boiler.

Refrigerator operation diagram

Electric motor

The engine is the main component of a household appliance. Designed to circulate coolant (freon) through the tubes.

The engine consists of two units:

• electric motor;
• compressor.

An electric motor converts electrical current into mechanical energy. The unit consists of two parts - a rotor and a stator.

The stator housing is made of several copper coils. The rotor has the appearance of a steel shaft. The rotor is connected to the engine piston system.

When the motor is connected to the power supply, electromagnetic induction occurs in the coils. It is the cause of torque. Centrifugal force causes the rotor to rotate.

Did you know that the refrigerator accounts for 10% of all electricity consumed. An open appliance door increases electricity consumption several times.

When the engine rotor rotates, the piston moves linearly. The front wall of the piston compresses and discharges the working fluid to working condition.

Refrigerator motor position

In modern refrigeration systems, the electric motor is located inside the compressor. This arrangement blocks the gas from spontaneously leaking.

To reduce vibrations, the engine is mounted on a springy metal suspension. The spring can be located outside or inside the device. In modern units, the spring is located inside the motor housing. This allows you to effectively dampen vibrations during operation of the device.

Capacitor

It is a serpentine pipeline with a diameter of up to 5 millimeters. Designed to remove heat from the working fluid into the environment. The capacitor is located on the rear outer surface of the device.

Evaporator

It is a system of thin tubes. Designed to evaporate the working fluid and cool the surrounding space. Located inside or outside the freezer.

Compressor device

Capillary tube

Designed to reduce gas pressure. It has a diameter of 1.5 to 3 millimeters. Located in the area between the evaporator and condenser.

Filter drier

Designed to purify working gas from moisture. It looks like a copper tube with a diameter of 10 to 20 mm. The ends of the tube are extended and hermetically sealed with the capillary tube and capacitor.

Attention! The filter drier has a one-way operating principle. The device is not designed to operate in reverse mode. If the filter is installed incorrectly, the unit may fail.

Inside the tube there is zeolite - a mineral filler with a highly porous structure. Barrier nets are installed at both ends of the tube.

Filter drier

A metal mesh with cell sizes up to 2 mm is installed on the capacitor side. A synthetic mesh is installed on the side of the capillary tube. The cell sizes of such a grid are tenths of a millimeter.

Boiler

It is a metal container. Installed in the area between the evaporator and the compressor inlet. Designed to bring freon to a boil with subsequent evaporation.

Serves to protect the engine from liquid ingress. Ingress of working fluid can lead to its failure.

How does a refrigerator work?

The main principle of operation of any refrigerator is based on two working operations:

1. Extraction of thermal energy from the device into the surrounding space.
2. Concentration of cold inside the device body.

A refrigerant called freon is used to extract heat. It is a gaseous substance based on ethane, fluorine and chlorine. Freon has the unique ability to pass from a gaseous state to a liquid state and back. The transition from one state to another occurs when pressure changes.

The operation of the cooling system is as follows. The compressor sucks freon inside. An electric motor operates inside the device. The engine drives the piston. When the piston moves, the gas is compressed.

Schematic diagram of the refrigerator

The gas compression process is divided into two stages. At the first stage, the piston returns. When the piston moves, the intake valve opens. Through the open hole, freon enters the gas chamber.

In the second stage, the piston moves in the opposite direction. During the reverse movement, the piston compresses the gas. The compressed freon presses on the outlet valve plate. The pressure in the chamber rises sharply. As the pressure increases, the gas heats up to a temperature of 100° C. The exhaust valve opens and releases the gas to the outside.

The heated freon from the chamber enters the external heat exchanger (condenser). Along the way through the condenser, freon gives off heat to the outside. At the end point of the condenser, the gas temperature decreases to 55° C.

Did you know that the very first refrigerators used sulfur dioxide as a refrigerant? Such devices were very dangerous due to the high probability of system depressurization.

During the heat transfer process, gas condensation occurs. Freon turns from a gaseous state into a liquid.

From the condenser, liquid freon enters the filter drier. Here moisture is absorbed by a special sorbent. From the filter, freon gas enters the capillary tube.

The capillary tube plays the role of a kind of plug (obstacle). At the entrance to the tube, the gas pressure decreases. The refrigerant turns into liquid. Freon flows from the capillary tube to the evaporator. When the pressure drops, freon evaporates. Along with the pressure, the gas temperature also drops. When freon enters the evaporator, the temperature is – 23° C.

Freon passes through a heat exchanger inside the refrigerator compartment. The cooled gas removes heat from the inner surface of the evaporator tubes. When heat is released, the interior of the refrigerator compartment is cooled.

After the evaporator, freon is sucked into the compressor. The closed cycle repeats.

Main types of cooling systems

Based on the principle of operation, the following types of refrigerators are distinguished:

• compression;
• adsorption;
• thermoelectric;
• steam ejector.

In compression units, the movement of refrigerant is carried out by changing the pressure in the system. The pressure of the working fluid is regulated by the compressor. Compressor refrigeration systems are the most common type of refrigeration device.

In absorption units, the movement of the refrigerant occurs due to its heating from the heating system. Ammonia is used as the working mixture. The disadvantage of the system is the high danger and complexity of maintenance. This type of household appliance is obsolete and has now been discontinued.

Did you know that the very first refrigerator was produced by the American company General Electric back in 1911? The device was made of wood. Sulfur dioxide was used as a refrigerant.

The main principle of operation of thermoelectric refrigerators is based on the absorption of heat during the interaction of two conductors during the passage of electric current through them. This principle is known as the Peltier Effect. The advantage of the device is its high reliability and durability. The disadvantage is the high cost of semiconductor systems.

Steam ejector units use water. The role of the propulsion system is performed by the ejector. The working fluid enters the evaporator. Here the liquid boils to form water vapor. When heat is generated, the water temperature drops sharply.

Chilled water is used to cool food. Water vapor is removed by an ejector to the condenser. In the condenser, the water vapor is cooled, turns into condensate and returns to the evaporator. The advantage of such installations is their simplicity of design, safety, and environmental friendliness. The disadvantage of the steam ejector system is the significant consumption of water and electricity for heating it.

Working principle of absorption refrigerators

The operation of absorption devices is based on the circulation and evaporation of liquid refrigerant. Ammonia is used as a refrigerant. The role of an absorbent (absorber) is performed by a water-based ammonia solution.

Scheme of operation of the absorption device

Hydrogen and sodium chromate are added to the cooling system of the apparatus. Hydrogen is intended to regulate system pressure. Sodium chromate protects the inner walls of the tubes from corrosion.

Did you know that old Soviet refrigerators use chlorine-based R12 freon as a cooling mixture. The main disadvantage is its destructive effect on the Earth's ozone layer.

When connected to the power supply, the generator-boiler heats up the working fluid. The working mixture is an ammonia aqueous solution. The ammonia solution is in a special tank.

Heating the refrigerant causes ammonia to evaporate. Ammonia vapor enters the condenser. Here the ammonia condenses and turns into a liquid.

Liquefied ammonia enters the evaporator. From here, liquid ammonia is mixed with hydrogen. The pressure difference between the two substances causes ammonia to evaporate. The evaporation process is accompanied by the release of heat and cooling of the ammonia to -4° C. Together with the ammonia, the evaporator is cooled.

The cooled evaporator absorbs heat from the surrounding area. After evaporation, the ammonia enters the adsorber. The adsorber contains clean water. Here the ammonia is mixed with water. The ammonia solution enters the tank. The ammonia solution from the reservoir enters the generator-boiler and the closed cycle is repeated.

Aqueous solutions of acetone, lithium bromide, and acetylene can be used as a substitute for ammonia.

The advantage of absorption devices is the quiet operation of the units.

Operating principle of a self-defrosting refrigerator

The defrosting process in units with a self-defrosting system occurs automatically.

There are two types of self-defrosting systems:

1. Drip.
2. Windy (No frost).

In devices with a drip system, the evaporator is located on the rear wall of the device. During operation of the device, frost forms on the back wall. When defrosting, frost flows through special gutters into the lower part of the device. The compressor, heated to a high temperature, evaporates the liquid.

In installations with a wind system, cold air from the evaporator on the rear wall is blown into the housing by a special fan. During the defrosting cycle, frost flows down the grooves into a special hole.

Industrial refrigerators

Industrial devices differ from household devices in the installation power and the size of the cooling chambers. The engine power of the equipment reaches several tens of kilowatts. The operating temperature of freezers ranges from + 5 to – 50° C.

Did you know that the largest industrial refrigerator occupies 24 km2 of area. This giant is located in Geneva (Switzerland) and serves for scientific purposes during the operation of the hadron collider.

Industrial units are designed for cooling and deep freezing large quantities of food. The volume of freezers ranges from 5 to 5000 tons. Used in procurement and processing enterprises.

Operating principle of an inverter refrigerator

Inverter compressors are designed to accumulate and convert direct current into alternating current with a voltage of 220 V. The operating principle is based on the ability to smoothly control the engine shaft speed.

Inverter motor device

When turned on, the inverter quickly picks up the required number of revolutions to create the required temperature inside the case. When the specified parameters are reached, the device goes into standby mode. As soon as the temperature inside the housing rises, the temperature sensor is triggered and the engine speed increases.

Refrigerator thermostat device

The thermostat is designed to maintain a set temperature inside the system. The device is hermetically sealed at one end of the capillary tube. The other end of the capillary tube is connected to the evaporator.

The main element of the thermostat device of any refrigerator is the thermostat. The design of the thermal relay consists of a bellows and a power lever.

Thermostat device

A bellows is a corrugated spring containing freon in its rings. Depending on the temperature of the freon, the spring is compressed or stretched. As the refrigerant temperature decreases, the spring contracts.

Did you know that modern household refrigerators use R600a freon based on isobutane. This refrigerant does not destroy the ozone layer of the planet and does not cause a greenhouse effect.

Under the influence of compression, the lever closes the contacts and connects the compressor to operation. As the temperature rises, the spring stretches. The power lever opens the circuit and the motor turns off.

Refrigerator without electricity - fact or fiction?

Nigerian resident Mohammed Ba Abba received a patent for a refrigerator without electricity in 2003. The device consists of clay pots of different sizes. The vessels are stacked into each other according to the Russian “matryoshka” principle.

Refrigerator without electricity

The space between the pots is filled with wet sand. A damp cloth is used as a cover. Under the influence of hot air, moisture from the sand evaporates. The evaporation of water leads to a decrease in the temperature inside the vessels. This allows you to store food for a long time in hot climates without using electricity.

Knowledge of the structure and operating principle of the refrigerator will allow you to perform simple repairs of the device yourself. If the system is configured correctly, then the device will work for many years. For more complex malfunctions, you should contact service center specialists.

The structure, as well as the principle of operation of a refrigerator, is superficially studied in physics lessons, however, not every adult has an idea of ​​how a refrigerator works? Consideration and analysis of the main technical aspects will help in practice to extend the service life and improve the performance of a household refrigerator.

Compression refrigerator device

It is best to consider the design of a refrigerator using a compression sample as an example, since these devices are most often used in everyday life:

1. – a device that uses a piston to push refrigerant (gas), creating different pressures in different parts of the system;
2. Evaporator– a container into which liquefied gas enters, absorbing heat from the refrigeration chamber;
3. Capacitor– a container in which compressed gas releases heat to the surrounding space;
4. Thermostatic valve– a device that maintains the required refrigerant pressure;
5. Refrigerant- a mixture of gases (most often freon is used), which, under the influence of the compressor, circulates in the system, taking and releasing heat in its different parts.

Refrigerator operation

The structure of the refrigerator, as well as the operating principle of a refrigerator with one chamber, can be understood by watching the corresponding video:

The most important aspect in understanding how a compression machine works is that it does not create cold as such. Cold occurs due to heat being taken from inside the device and sent outside. This function is performed by freon. When entering the evaporator, which usually consists of aluminum tubes or plates welded together, freon vapor absorbs heat.

This you need to know: in old-style refrigerators, the evaporator body is also the body of the freezer. When defrosting this chamber, you should not use sharp objects to remove ice, since all the freon will evaporate through the broken evaporator housing. A refrigerator without refrigerant becomes inoperative and is subject to expensive repairs.

Then, under the influence of the compressor, the freon vapor leaves the evaporator and goes into the condenser (a system of tubes that are located inside the walls and on the back of the unit). In the condenser, the refrigerant cools, gradually becoming liquid. On its way to the evaporator, the gas mixture is dried in a filter drier and also passes through a capillary tube. At the entrance to the evaporator, due to an increase in the internal diameter of the tube, the pressure drops and the gas becomes vaporous. The cycle is repeated until the required temperature is reached.

How does a compressor work?

Using a piston, the compressor moves the refrigerant from one pipe system to another, alternately changing the physical state of the freon. When refrigerant is supplied to the condenser, the compressor strongly compresses it, causing the freon to heat up. After traveling a long way through the labyrinth of condenser tubes, the cooled freon enters the evaporator through an expanded tube. Due to a sudden change in pressure, the refrigerant quickly cools. Now freon vapor is able to absorb a certain dose of heat and pass into the condenser tube system.

In household appliances, completely sealed compressor housings are used that do not allow the working gas mixture to pass through. For the purpose of tightness, the electric motor that drives the piston is also located inside the compressor housing. All rubbing parts inside the motor-compressor are lubricated with special oil.

The electrical diagram of the refrigerator can be useful for those who are ready to independently diagnose and repair the refrigerator:

Design and principle of operation of a two-chamber refrigerator

The design of a two-chamber refrigerator differs from a single-chamber one in that each compartment has its own evaporator. Unlike its predecessors, in two-chamber devices both compartments are isolated from each other. In such devices, the freezer is usually located at the bottom, and the refrigeration part is at the top. The operating principle of a two-chamber refrigerator is that the working gas mixture first cools the freezer evaporator to a certain sub-zero temperature. Only after this does the freon pass into the evaporator of the refrigeration compartment. After the evaporator of the refrigeration chamber reaches a certain sub-zero temperature, the thermostat is activated, stopping the motor.

In everyday life, two-chamber devices with one compressor are more often used. In units with two motors, the principle of operation of the refrigerator does not change significantly, just one compressor works for the freezer, the other for the refrigerator compartment. It is generally accepted that running a refrigerator with one compressor is more economical, but in reality this is not always the case. After all, in a device with two motors, you can turn off one of the cameras that is not needed. The operation of a two-chamber refrigerator with one compressor always involves simultaneous cooling of both chambers.

Refrigerator and ambient temperature

The operating instructions for most household refrigerators indicate at what temperature it is best to operate it. The minimum acceptable temperature is +5 Celsius. Can a refrigerator operate in cold conditions, especially in freezing temperatures? Let's look at possible problems:

• Thermostat is not working properly. Under normal conditions, the thermostat breaks the electrical circuit when the required temperature is reached. When the air inside warms up, the thermostat will close the electrical circuit again and the motor will resume operation. In conditions of sub-zero ambient temperatures, the thermostat most likely will not turn on the compressor again, since the heat inside the chamber simply has nowhere to come from;
• Difficulty starting the compressor. In older devices, R12 and R22 refrigerants were most often used. For normal operation, refrigeration oils were used, which at temperatures below +5C become too thick, which means that starting and moving the piston will be difficult;
• The appearance of the “wet running” effect. Since there is no heat in the refrigerator, the operation of the evaporator is disrupted. Steam saturated with droplets enters the compressor. As a result of prolonged operation in such conditions, the entire mechanics of the motor will be damaged.

In simple words, a gentle attitude towards the device will significantly extend its service life.

Working principle of absorption refrigerator

In an absorption apparatus, cooling is associated with the evaporation of the working mixture. Most often this substance is ammonia. The movement of refrigerant occurs as a result of the dissolution of ammonia in water. From the absorber, the ammonia solution enters the desorber, and then into the reflux condenser, in which the mixture is separated into its original components. In the condenser, the ammonia becomes liquid and is sent back to the evaporator.

Liquid movement is provided by jet pumps. In addition to water and ammonia, the system contains hydrogen or other inert gas.

Most often, an absorption refrigerator is in demand where it is impossible to use a conventional compression analogue. In everyday life, such devices are rarely used, since they are relatively short-lived, and the refrigerant is a toxic substance.

Operation and rest mode of the compression refrigerator

Many users are interested in the question: how long should a refrigerator run? The only true criterion for the normal operation of a home appliance is the sufficient degree of freezing and cooling of food in it.

How long a refrigerator can work and how long it should rest is not specified in any instructions, however, there is a concept of “optimal working time coefficient”. To calculate it, the duration of the working cycle is divided into the sum of the working and non-working cycle. So, for example, a refrigerator that worked for 15 minutes with a further 25-minute rest will have a coefficient of 15/(15+25) = 0.37. The lower this coefficient, the better the refrigerator works. If the result of the calculation is a number less than 0.2, then most likely the temperature in the refrigerator is set incorrectly. A coefficient greater than 0.6 means that the tightness of the unit is broken.

How does a No Frost refrigerator work?

Refrigerators with a no frost system have only one evaporator, which is hidden in the freezer behind a plastic wall. The cold is transferred from it using a fan, which is located behind the evaporator. Through the technological openings, cold air enters the freezer, and then into the refrigerator.

In contact with

Cooling of various objects - food, water, other liquids, air, technical gases, etc. to temperatures below ambient temperature occurs using various types of refrigeration machines. A refrigeration machine, by and large, does not produce cold; it is only a kind of pump that transfers heat from less heated bodies to more heated ones. The cooling process is based on the constant repetition of the so-called. reverse thermodynamic or in other words refrigeration cycle. In the most common vapor-compression refrigeration cycle, heat transfer occurs during phase transformations of the refrigerant - its evaporation (boiling) and condensation due to the consumption of energy supplied from outside.

The main elements of the refrigeration machine, with the help of which its operating cycle is realized, are:

• compressor - an element of the refrigeration cycle that increases the pressure of the refrigerant and its circulation in the circuit of the refrigeration machine;
• A throttling device (capillary tube, thermostatic valve) serves to regulate the amount of refrigerant entering the evaporator depending on the superheat at the evaporator.
• evaporator (cooler) - a heat exchanger in which the refrigerant boils (with heat absorption) and the cooling process itself;
• condenser - a heat exchanger in which, as a result of the phase transition of the refrigerant from a gaseous to a liquid state, the removed heat is discharged into the environment.

In this case, it is necessary to have other auxiliary elements in the refrigeration machine, such as electromagnetic (solenoid) valves, instrumentation, sight glasses, filter driers, etc. All elements are connected to each other in a sealed internal circuit using thermally insulated pipelines. The refrigeration circuit is filled with refrigerant in the required quantity. The main energy characteristic of a refrigeration machine is the refrigeration coefficient, which is determined by the ratio of the amount of heat removed from the cooled source to the energy expended.

Refrigerators are of several types, depending on the principles of operation and the refrigerant used. The most common are vapor compression, steam ejector, absorption, air and thermoelectric.

Refrigerant

Refrigerant is the working substance of the refrigeration cycle, the main characteristic of which is its low boiling point. Various hydrocarbon compounds, which may contain chlorine, fluorine or bromine atoms, are most often used as refrigerants. The refrigerant can also be ammonia, carbon dioxide, propane, etc. Air is rarely used as a refrigerant. In total, about a hundred types of refrigerants are known, but only about 40 are manufactured industrially and widely used in refrigeration, cryogenics, air conditioning and other industries. These are R12, R22, R134A, R407C, R404A, R410A, R717, R507 and others. The main areas of application of refrigerants are the refrigeration and chemical industries. In addition, some freons are used as propellants in the production of various products in aerosol packaging; foaming agents in the production of polyurethane and heat-insulating products; solvents; and also as substances that inhibit the combustion reaction for fire extinguishing systems of various high-risk objects - thermal and nuclear power plants, civil sea vessels, warships and submarines.

Thermostatic expansion valve (TRV)

Thermostatic expansion valve (TEV), one of the main components of refrigeration machines, is known as the most common element for throttling and precisely regulating the flow of refrigerant into the evaporator. The expansion valve uses a needle-type valve adjacent to a poppet-shaped base as a refrigerant flow regulator. The amount and flow rate of the refrigerant is determined by the flow area of ​​the expansion valve and depends on the temperature at the outlet of the evaporator. When the temperature of the refrigerant leaving the evaporator changes, the pressure inside this system changes. When the pressure changes, the flow area of ​​the expansion valve changes and, accordingly, the refrigerant flow changes.

The thermal system is filled at the factory with a precisely defined amount of the same refrigerant, which is the working substance of this refrigeration machine. The task of the expansion valve is to throttle and regulate the refrigerant flow at the inlet of the evaporator so that the cooling process occurs most efficiently in it. In this case, the refrigerant must completely transform into a vapor state. This is necessary for reliable operation of the compressor and to prevent it from operating so-called. “wet” stroke (i.e. fluid compression). The thermal cylinder is attached to the pipeline between the evaporator and the compressor, and at the attachment point it is necessary to ensure reliable thermal contact and thermal insulation from the effects of ambient temperature. Over the last 15-20 years, electronic expansion valves have become widespread in refrigeration technology. They differ in that they do not have an external thermal system, and its role is played by a thermistor attached to the pipeline behind the evaporator, connected by a cable to a microprocessor controller, which in turn controls the electronic expansion valve and, in general, all the working processes of the refrigeration machine.

The solenoid valve is used for on-off regulation (“open-closed”) of the supply of refrigerant to the evaporator of the refrigeration machine or for opening and closing certain sections of pipelines from an external signal. When there is no power to the coil, the valve disc, under the influence of a special spring, keeps the solenoid valve closed. When power is applied, the electromagnet core, connected by a rod to the plate, overcomes the force of the spring and is drawn into the coil, thereby lifting the plate and opening the flow area of ​​the valve to supply refrigerant.

The sight glass in the refrigeration machine is designed to determine:

1. refrigerant condition;
2. the presence of moisture in the refrigerant, which is determined by the color of the indicator.

The sight glass is usually mounted in the pipeline at the outlet of the storage receiver. Structurally, the viewing glass is a sealed metal housing with a transparent glass window. If, when the refrigeration machine is operating, a flow of liquid with individual bubbles of vaporous refrigerant is observed in the window, this may indicate insufficient charging or other malfunctions in its functioning. A second sight glass can also be installed at the other end of the above pipeline, in close proximity to the flow regulator, which can be a solenoid valve, expansion valve or capillary tube. The color of the indicator indicates the presence or absence of moisture in the refrigeration circuit.

The filter drier or zeolite cartridge is another important element of the refrigeration machine circuit. It is necessary to remove moisture and mechanical impurities from the refrigerant, thereby protecting against clogging of the expansion valve. It is usually mounted using soldered or fitting connections directly into the pipeline between the condenser and the expansion valve (solenoid valve, capillary tube). Most often, it is structurally a piece of copper pipe with a diameter of 16...30 and a length of 90...170 mm, rolled on both sides and with connecting pipes. Inside, two metal filter meshes are installed at the edges, between which there is a granular (1.5...3.0 mm) adsorbent, usually a synthetic zeolite. This is the so-called disposable filter drier, but there are reusable filter designs with a collapsible housing and threaded pipeline connections that require only occasional replacement of the internal zeolite cartridge. Replacing a disposable filter-drier or cartridge is necessary after each opening of the internal circuit of the refrigeration machine. There are unidirectional filters designed to work in “cold only” systems and bidirectional filters used in “heat-cold” units.

Receiver

The receiver is a sealed cylindrical storage tank of various capacities, made of steel sheet, and serves to collect liquid refrigerant and its uniform supply to the flow regulator (TRV, capillary tube) and to the evaporator. There are receivers of both vertical and horizontal types. There are linear, drainage, circulation and protective receivers. The linear receiver is installed using soldered connections in the pipeline between the condenser and the expansion valve and performs the following functions:

• ensures continuous and uninterrupted operation of the refrigeration machine under various thermal loads;
• is a hydraulic seal that prevents refrigerant vapor from entering the expansion valve;
• performs the function of an oil and air separator;
• Frees the condenser pipes from liquid refrigerant.

Drain receivers are used to collect and store the entire amount of charged refrigerant during repair and service work associated with depressurization of the internal circuit of the refrigeration machine.

Circulation receivers are used in pump-circulation circuits for supplying liquid refrigerant to the evaporator to ensure continuous operation of the pump and are installed in the pipeline after the evaporator at the point with the lowest elevation for free drainage of liquid into it.

Protective receivers are designed for pumpless circuits for supplying freon to the evaporator; they are installed together with liquid separators in the suction pipeline between the evaporator and the compressor. They serve to protect the compressor from possible wet running.

Pressure regulator - an automatically controlled control valve used to reduce or maintain refrigerant pressure by changing the hydraulic resistance to the flow of liquid refrigerant passing through it. Structurally, it consists of three main elements: a control valve, its actuator and a measuring element. The actuator directly acts on the valve disc, changing or closing the flow area. The measuring element compares the current and set value of the refrigerant pressure and generates a control signal for the control valve actuator. In refrigeration technology, there are low pressure regulators, more often called pressure switches. They control the boiling pressure in the evaporator and are installed in the suction pipe downstream of the evaporator. High pressure regulators are called manocontrollers. They are most often used in refrigeration machines with air-cooled condenser to maintain the minimum required condensation pressure when the outside air temperature decreases during the transitional and cold period of the year, thereby providing the so-called. winter regulation. The pressure controller is installed in the discharge pipeline between the compressor and the condenser.

Operating principle of the refrigeration unit

To obtain artificial cold, technology uses the property of a liquid to change its boiling point depending on pressure.

To turn a liquid into steam, a certain amount of heat must be supplied to it. On the contrary, the transformation of steam into liquid (the process of condensation) occurs when heat is removed from the steam.

The refrigeration unit consists of four main parts: a compressor, a condenser, a control valve and an air cooler (evaporator), connected in series with each other by pipelines.

In this scheme, a refrigerant circulates in a closed loop - a substance that can boil at low temperatures, depending on the vapor pressure in the air cooler. The lower this pressure, the lower the boiling point. The boiling process of the refrigerant is accompanied by the removal of heat from the environment in which the air cooler is located, as a result of which this environment is cooled.

The refrigerant vapors formed in the air cooler are sucked off by the compressor, compressed in it and pumped into the condenser. During the compression process, the pressure and temperature of the refrigerant vapor increases. Thus, the compressor creates, on the one hand, a reduced pressure in the air cooler, necessary for the refrigerant to boil at a low temperature, and, on the other, an increased discharge pressure, at which the transfer of the refrigerant from the compressor to the condenser is possible.

In the condenser, hot refrigerant vapors condense, i.e., they are converted into liquid. Vapor condensation occurs as a result of heat being removed from it by air cooling the condenser.

To obtain cold, it is necessary that the boiling (evaporation) temperature of the refrigerant be lower than the temperature of the cooled medium.

The AR-3 refrigeration unit is a single unit mounted on a frame with a heat-insulating wall that separates the evaporative part (air cooler) from the rest of the equipment. The evaporative part enters the opening made in the front wall of the cargo space. Outside air is sucked through the condenser by an axial fan into the engine room.

An air cooler fan is located on the same shaft as the condenser fan, which circulates air in the cargo area.

Thus, in the AR-3 refrigeration unit there are two independent air systems:
— cooled air circulation system in the cargo space (air from the floor of the cargo space through a guide air duct is sucked by an axial fan into the air cooler, cooled and discharged under the ceiling of the cargo space);
— condenser cooling system.

An axial fan located inside the engine room draws air from the environment through the louvers of the front panel of the body, enters the condenser, cools it and throws it out through the louvres installed on the side doors of the engine room.

To cool the carburetor engine, air is taken in through a special window in the front wall of the body and released inside the engine compartment. Heated air from the engine room exits through the side door louvres.

The control panel and all automation devices, as well as measuring instruments, are located on the left (along the direction of the vehicle) side of the refrigeration unit and have free access.

Fuel is supplied to the carburetor engine from a tank mounted in the upper part of the unit.

The refrigeration unit is a closed hermetic system consisting of four main parts: an air cooler, a freon compressor, a condenser and a thermostatic valve, connected in series by pipelines. This system is filled with the refrigerant Freon-12, which continuously circulates in it, passing1 from one part to another.

The compressor sucks freon vapors formed during boiling from the air cooler 8 and compresses them to condensation pressure. Simultaneously with the increase in vapor pressure, their temperature also increases to 70-80 °C. Heated freon vapor from the compressor is pumped through a pipeline into the condenser. In the condenser, freon vapor condenses, i.e., it turns into liquid. Condensation of vapors occurs as a result of removal from them. heat by air blowing on the outer surface of the condenser.

Liquid freon from the condenser enters the receiver (spare container). From the receiver, liquid freon is directed to the heat exchanger, where, passing through the coils, it is supercooled due to heat exchange with cold freon vapor moving towards it from the air cooler. Then the liquid freon enters the filter drier, where it is cleaned of moisture and contaminants by a desiccant substance - silica gel.

Rice. 2. Refrigeration
1 - control panel; 2 - instrument panel; 3 - fan block; 4 - condenser 5 - filter drier; 9- heat exchanger; 10- thermal insulation wall; 1st engine UD-2; 15 - relay-regulator PP24-G; 16 - thermostatic pressor FV-6; 19 - electric motor A-51-2;

From the filter-drier, liquid freon is directed to a temperature control valve, which serves to regulate the amount of freon entering the air cooler (evaporator).

In a thermostatic valve, passing through a small-diameter hole, freon is throttled, i.e., it sharply lowers its pressure. In this case, its pressure decreases from condensation pressure to evaporation pressure.

A decrease in pressure leads to a decrease in freon temperature. Freon in the form of a vapor-liquid mixture enters the air cooler through a liquid distributor, and the cycle is repeated.

Freon, flowing through the air cooler tubes at low pressure, boils intensely and, evaporating, passes from a liquid state to a vapor state.

The heat required for evaporation (latent heat of evaporation) is absorbed by freon through the walls of the air cooler from the cargo room air blown by a fan through the ribbed surface of the air cooler.

Rice. 3. Diagram of air flow in a refrigeration unit: A-air flow for cooling the condenser; B - air flow for cooling a carburetor engine

Under these conditions, the air temperature of the cargo space decreases and the products located in the cargo space, transferring their heat to the colder air, are cooled.

The thermostatic valve divides the freon system into two parts: a high-pressure line (discharge or condensation pressure) - from the discharge cavity of the compressor to the thermostatic valve, and a low-pressure line (suction or evaporation pressure) - from the thermostatic valve to the suction cavity of the compressor.

From the air cooler, freon vapors are sucked through the suction pipeline by a compressor and fed into the heat exchanger, where, passing through the interpipe space, they are overheated by liquid freon passing through the coil. Then the freon vapor enters the compressor, and the further described process of freon circulation in the refrigeration unit occurs in a closed cycle.

In the condenser, freon, turning from vapor into liquid, gives off heat to the blown air from the surrounding atmosphere, and in the air cooler, turning from liquid into vapor, it absorbs heat from the air in the cargo room, thereby lowering the temperature in the cargo room.

Thus, in the refrigeration unit, the refrigerant circulates - freon-12, which itself is not consumed, and only the mechanical energy of the compressor driven by a carburetor or electric motor is expended to produce cold.

The power of a refrigeration unit is determined by the refrigeration capacity per hour of operation and is measured by the amount of heat (kilocalories per hour) that the refrigeration unit can remove within an hour from the cooled environment, in this case from the cargo area of ​​the refrigerator.

The compressor of the refrigeration unit is driven through a V-belt drive by a carburetor engine, and when operating from an electrical network, by an electric motor.

From the compressor pulley, the movement is also transmitted by a V-belt to the DC generator and the fan shaft, which creates air flows through the condenser and air cooler.

The temperature (from -15° to +4 °C) in the cargo area of ​​the body is maintained automatically using a two-position thermal relay TDDA.

When it is necessary to maintain a positive temperature in the cargo area of ​​the body, the refrigeration capacity of the installation can be sharply reduced using a control valve on the suction pipe. In this case, the valve spool must be turned clockwise all the way.

Refrigerating machines and installations are designed to artificially reduce and maintain a low temperature below the ambient temperature from 10 °C to -153 °C in a given refrigerated object. Machines and installations for creating lower temperatures are called cryogenic. The removal and transfer of heat is carried out due to the energy consumed. The refrigeration unit is carried out according to the project, depending on the design specification that defines the object being cooled, the required range of cooling temperatures, energy sources and types of cooling medium (liquid or gaseous).

A refrigeration unit may consist of one or more refrigeration machines equipped with auxiliary equipment: a power and water supply system, instrumentation, regulation and control devices, as well as a heat exchange system with the cooled object. A refrigeration unit can be installed indoors, outdoors, in transport and in various devices in which it is necessary to maintain a given low temperature and remove excess air moisture.

The heat exchange system with the cooled object can be with direct cooling by a refrigerant, in a closed system, in an open system, as when cooling with dry ice, or with air in an air refrigeration machine. A closed system may also have an intermediate refrigerant that transfers the cold from the refrigeration unit to the object being cooled.

The creation of the first ammonia steam-compressor refrigeration machine by Karl Linde in 1874 can be considered the beginning of the development of refrigeration engineering on a large scale. Since then, many varieties of refrigeration machines have appeared, which can be grouped according to the principle of operation as follows: steam-compression, simply called compressor, usually with an electric drive; heat-using refrigeration machines: absorption refrigeration machines and steam ejector; air-expansion ones, which are more economical than compressor ones at temperatures below -90 ° C, and thermoelectric ones, which are built into devices.

Each type of refrigeration units and machines has its own characteristics, according to which their area of ​​application is selected. Currently, refrigeration machines and installations are used in many areas of the national economy and in everyday life.

2. Thermodynamic cycles of refrigeration units

The transfer of heat from a less heated to a more heated source becomes possible if any compensating process is organized. In this regard, the cycles of refrigeration units are always implemented as a result of energy consumption.

In order for the heat removed from the “cold” source to be transferred to the “hot” source (usually the surrounding air), it is necessary to raise the temperature of the working fluid above the ambient temperature. This is achieved by rapid (adiabatic) compression of the working fluid with the expenditure of work or the supply of heat to it from the outside.

In reverse cycles, the amount of heat removed from the working fluid is always greater than the amount of heat supplied, and the total work of compression is greater than the total work of expansion. Due to this, installations operating on similar cycles are energy consumers. Such ideal thermodynamic cycles of refrigeration units have already been discussed above in paragraph 10 of topic 3. Refrigeration units differ in the working fluid used and the principle of operation. The transfer of heat from a “cold” source to a “hot” one can be carried out due to the cost of work or the cost of heat.

2.1. Air refrigeration units

In air refrigeration units, air is used as a working fluid, and heat is transferred from a “cold” source to a “hot” source through the expenditure of mechanical energy. The decrease in air temperature necessary to cool the refrigeration chamber is achieved in these installations as a result of its rapid expansion, in which the time for heat exchange is limited, and the work is mainly done due to internal energy, due to which the temperature of the working fluid drops. The diagram of the air refrigeration unit is shown in Fig. 7.14

Rice. 14. : ХК - refrigerating chamber; K - compressor; TO - heat exchanger; D - expansion cylinder (expander)

The temperature of the air entering from the refrigeration chamber XK into the compressor cylinder K rises as a result of adiabatic compression (process 1 - 2) above the ambient temperature T3. When air flows through the tubes of the heat exchanger TO, its temperature at a constant pressure decreases - theoretically to the ambient temperature T3. In this case, the air releases heat q (J/kg) to the environment. As a result, the specific volume of air reaches a minimum value v3, and the air flows into the cylinder of the expansion cylinder - expander D. In the expander, due to adiabatic expansion (process 3-4), useful work is performed equivalent to the darkened area 3-5-6-4-3 , the air temperature drops below the temperature of the items cooled in the refrigerator compartment. The air cooled in this way enters the refrigerating chamber. As a result of heat exchange with cooled objects, the air temperature at constant pressure (isobar 4-1) rises to its initial value (point 1). In this case, heat q2 (J/kg) is supplied from the cooled objects to the air. The value q 2, called cooling capacity, is the amount of heat received by 1 kg of working fluid from cooled objects.

2.2. Steam compressor refrigeration units

In steam compressor refrigeration units (SCRU), low-boiling liquids are used as the working fluid (Table 1), which makes it possible to implement processes of heat supply and removal according to isotherms. For this purpose, the processes of boiling and condensation of the working fluid (refrigerant) at constant pressure values ​​are used.

Table 1.

In the 20th century, various freons based on chlorofluorocarbons were widely used as refrigerants. They caused active destruction of the ozone layer, and therefore their use is currently limited, and the K-134A refrigerant (discovered in 1992) based on ethane is used as the main refrigerant. Its thermodynamic properties are close to those of freon K-12. Both refrigerants have slightly different molecular weights, heats of vaporization and boiling points, but, unlike K-12, K-134A refrigerant is not aggressive towards the Earth’s ozone layer.

The PKHU scheme and cycle in T-s coordinates are shown in Fig. 15 and 16. In the PKHU, the pressure and temperature are reduced by throttling the refrigerant as it flows through the pressure reducing valve RV, the flow area of ​​which can vary.

The refrigerant from the refrigerating chamber XK enters the compressor K, in which it is adiabatically compressed in the process 1 -2. The resulting dry saturated steam enters the pressurizer, where it condenses at constant pressure and temperature in process 2-3. The released heat q1 is transferred to a “hot” source, which in most cases is the surrounding air. The resulting condensate is throttled in a pressure reducing valve RV with a variable flow area, which allows you to change the pressure of the wet steam leaving it (process 3-4).

Rice. 15. Schematic diagram (a) and cycle in T-s-coordinates (b) of a steam compressor refrigeration unit: KD - capacitor; K - compressor; ХК - refrigerating chamber; RV - pressure reducing valve

Since the throttling process, which occurs at a constant enthalpy value (h3 - h), is irreversible, it is depicted with a dotted line. The wet saturated steam of a small degree of dryness obtained as a result of the process enters the heat exchanger of the refrigeration chamber, where, at constant values ​​of pressure and temperature, it evaporates due to the heat q2b taken from the objects in the chamber (process 4-1).

Rice. 16. : 1 - refrigerator; 2 - thermal insulation; 3 - compressor; 4 - compressed hot steam; 5 - heat exchanger; 6 - cooling air or cooling water; 7 - liquid refrigerant; 8 - throttle valve (expander); 9 - expanded, cooled and partially evaporated liquid; 10 - cooler (evaporator); 11 - evaporated coolant

As a result of “drying,” the degree of dryness of the refrigerant increases. The amount of heat taken from objects cooled in the refrigeration chamber in T-B coordinates is determined by the area of ​​the rectangle under the 4-1 isotherm.

The use of low-boiling liquids as a working fluid in PKhU allows one to approach the reverse Carnot cycle.

Instead of a throttling valve, an expansion cylinder - an expander - can be used to lower the temperature (see Fig. 14). In this case, the installation will operate according to the reverse Carnot cycle (12-3-5-1). Then the heat taken from the cooled objects will be greater - it will be determined by the area under the 5-4-1 isotherm. Despite the partial compensation of energy costs for driving the compressor by the positive work obtained during the expansion of the refrigerant in the expansion cylinder, such installations are not used due to their structural complexity and large overall dimensions. In addition, in installations with a variable-section throttle it is much easier to regulate the temperature in the refrigeration chamber.

Figure 17.

To do this, it is enough just to change the flow area of ​​the throttling valve, which leads to a change in pressure and the corresponding temperature of the saturated refrigerant vapor at the outlet of the valve.

Currently, instead of piston compressors, blade compressors are mainly used (Fig. 18). The greater efficiency of PKHU compared to air-based units is also evidenced by the fact that the ratio of the refrigeration coefficients of PKHU and the reverse Carnot cycle

In real steam compressor installations, not wet, but dry or even superheated steam enters the compressor from the evaporator heat exchanger of the refrigeration chamber (Fig. 17). This increases the dissipated heat q2, reduces the intensity of heat exchange between the refrigerant and the cylinder walls and improves the lubrication conditions for the compressor piston group. In such a cycle, some overcooling of the working fluid occurs in the condenser (isobar section 4-5).

Rice. 18.

2.3. Steam ejector refrigeration units

The cycle of a steam ejector refrigeration unit (Fig. 19 and 20) is also carried out using thermal rather than mechanical energy.

Rice. 19.: ХК - refrigerating chamber; E - ejector; KD - capacitor; RV - pressure reducing valve; N - pump; KA - boiler unit

Rice. 20.

In this case, compensating is the spontaneous transfer of heat from a more heated body to a less heated body. Steam of any liquid can be used as a working fluid. However, the cheapest and most accessible refrigerant is usually used - water vapor at low pressure and temperature.

From the boiler plant, steam enters the ejector nozzle E. When steam flows out at high speed, a vacuum is created in the mixing chamber behind the nozzle, under the influence of which refrigerant is sucked into the mixing chamber from the refrigeration chamber of the cold room. In the ejector diffuser, the speed of the mixture decreases, and the pressure and temperature increase. Then the vapor mixture enters the condenser KD, where it turns into liquid as a result of heat q1 being removed to the environment. Due to the multiple decrease in specific volume during the condensation process, the pressure decreases to a value at which the saturation temperature is approximately 20 °C. One part of the condensate is pumped by pump H into the boiler unit KA, and the other is subjected to throttling in the valve RV, as a result of which, with a decrease in pressure and temperature, wet steam with a slight degree of dryness is formed. In the heat exchanger-evaporator XK, this steam is dried at a constant temperature, taking away heat q2 from the cooled objects, and then again enters the steam ejector.

Since the mechanical energy costs for pumping the liquid phase in absorption and steam ejector refrigeration units are extremely small, they are neglected, and the efficiency of such units is assessed by the heat utilization coefficient, which is the ratio of the heat taken from the cooled objects to the heat used to implement the cycles.

To obtain low temperatures as a result of heat transfer to a “hot” source, other principles can be used. For example, the temperature can be lowered as a result of water evaporation. This principle is used in hot and dry climates in evaporative air conditioners.

3. Household and industrial refrigerators

A refrigerator is a device that maintains a low temperature in a heat-insulated chamber. They are typically used to store food and other items that require cold storage.

In Fig. 21 shows a diagram of the operation of a single-chamber refrigerator, and Fig. 22 - purpose of the main parts of the refrigerator.

Rice. 21.

Rice. 22.

The operation of the refrigerator is based on the use of a heat pump, which transfers heat from the working chamber of the refrigerator to the outside, where it is released to the external environment. In industrial refrigerators, the volume of the working chamber can reach tens and hundreds of m3.

Refrigerators can be of two types: medium-temperature food storage chambers and low-temperature freezers. However, recently, two-chamber refrigerators, which include both components, have become most widespread.

Refrigerators come in four types: 1 - compression; 2 - absorption; 3 - thermoelectric; 4 - with vortex coolers.

Rice. 23. : 1 - capacitor; 2 - capillary; 3 - evaporator; 4 - compressor

Rice. 24.

The main components of the refrigerator are:

1 - compressor receiving energy from the electrical network;

2 - condenser located outside the refrigerator;

3 - evaporator located inside the refrigerator;

4 - thermostatic expansion valve (TEV), which is a throttling device;

5 - refrigerant (a substance circulating in the system with certain physical characteristics - usually freon).

3.1. Operating principle of a compression refrigerator

The theoretical basis on which the operating principle of refrigerators is built, the diagram of which is shown in Fig. 23 is the second law of thermodynamics. The cooling gas in refrigerators does what is called reverse Carnot cycle. In this case, the main heat transfer is based not on the Carnot cycle, but on phase transitions - evaporation and condensation. In principle, it is possible to create a refrigerator using only the Carnot cycle, but in order to achieve high performance, either a compressor creating a very high pressure or a very large area of ​​​​cooling and heating heat exchanger will be required.

The refrigerant enters the evaporator under pressure through a throttling hole (capillary or expansion valve), where due to a sharp decrease in pressure it occurs evaporation liquid and turning it into steam. In this case, the refrigerant takes away heat from the internal walls of the evaporator, due to which the internal space of the refrigerator is cooled. The compressor draws refrigerant from the evaporator in the form of steam, compresses it, due to which the temperature of the refrigerant rises and pushes it into the condenser. In the condenser, the refrigerant heated as a result of compression cools, releasing heat to the external environment, and condenses, i.e. turns into liquid. The process is repeated again. Thus, in the condenser, the refrigerant (usually freon) under the influence of high pressure condenses and turns into a liquid state, releasing heat, and in the evaporator, under the influence of low pressure, the refrigerant boils and turns into a gaseous state, absorbing heat.

A thermostatic expansion valve (TEV) is necessary to create the required pressure difference between the condenser and the evaporator at which the heat transfer cycle occurs. It allows you to correctly (most completely) fill the internal volume of the evaporator with boiled refrigerant. The flow area of ​​the expansion valve changes as the thermal load on the evaporator decreases, and as the temperature in the chamber decreases, the amount of circulating refrigerant decreases. A capillary is an analogue of a expansion valve. It does not change its cross-section, but throttles a certain amount of refrigerant, depending on the pressure at the inlet and outlet of the capillary, its diameter and the type of refrigerant.

When the required temperature is reached, the temperature sensor opens the electrical circuit and the compressor stops. When the temperature rises (due to external factors), the sensor turns on the compressor again.

3.2. Working principle of absorption refrigerator

The absorption water-ammonia refrigerator uses the property of one of the widely used refrigerants - ammonia - to dissolve well in water (up to 1000 volumes of ammonia per 1 volume of water). The operating principle of an absorption refrigeration unit is shown in Fig. 26, and its circuit diagram is in Fig. 27.

Rice. 26.

Rice. 27. : GP - steam generator; KD - capacitor; РВ1, РВ2 - pressure reducing valves; ХК - refrigerating chamber; Ab - absorber; N - pump

In this case, the removal of gaseous refrigerant from the evaporator coil, required for any evaporative refrigerator, is carried out by absorbing it with water, the ammonia solution in which is then pumped into a special container (desorber/generator) and there it is decomposed into ammonia and water by heating. Vapors of ammonia and water from it under pressure enter a separation device (distillation column), where ammonia vapors are separated from water. Next, almost pure ammonia enters the condenser, where, upon cooling, it condenses and through the choke again enters the evaporator for evaporation. Such a heat engine can use a variety of devices, including jet pumps, to pump the refrigerant solution, and have no moving mechanical parts. In addition to ammonia and water, other pairs of substances can be used - for example, lithium bromide solution, acetylene and acetone. The advantages of absorption refrigerators are quiet operation, the absence of moving mechanical parts, the ability to operate from heating by direct combustion of fuel, the disadvantage is low cooling capacity per unit volume.

3.3. The working principle of a thermoelectric refrigerator

There are devices based on the Peltier effect, which consists in the absorption of heat by one of the junctions of thermocouples (dissimilar conductors) while releasing it at the other junction if current is passed through them. This principle is used, in particular, in cooler bags. It is possible to both lower and increase the temperature with the help of vortex tubes proposed by the French engineer Rank, in which the temperature changes significantly along the radius of the swirling vortex air flow moving in them.

Thermoelectric refrigerator is based on Peltier elements. It is silent, but is not widely used due to the high cost of cooling thermoelectric elements. However, small car refrigerators and drinking water coolers are often manufactured with Peltier cooling.

3.4. The principle of operation of a refrigerator using vortex coolers

Cooling is carried out due to the expansion of air pre-compressed by a compressor in blocks of special vortex coolers. They are not widespread due to their high noise level, the need to supply compressed (up to 1.0-2.0 MPa) air and its very high consumption, low efficiency. Advantages - greater safety (no electricity is used, no moving parts or dangerous chemical compounds), durability and reliability.

4. Examples of refrigeration units

Some diagrams and descriptions of refrigeration units for various purposes, as well as their photographs, are shown in Fig. 27-34.

Rice. 27.

Rice. 28.

Rice. 29.

Figure 32.

Rice. 33.

For example, compressor-condenser refrigeration units (AKK type) or compressor-receiver units (AKR type), shown in Fig. 34, are designed to operate with maintaining temperatures from +15 °C to -40 °C in chambers with a volume of 12 to 2500 m3.

The refrigeration unit includes: 1 - compressor-condenser or compressor-receiver unit; 2 - air cooler; 3 - thermostatic valve (TRV); 4 - solenoid valve; 5 - control panel.

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