What is the difference between the actual and theoretical cycles of refrigeration?

The theoretical cycle has assumed that refrigerants are excluded.

Loss of resistance along the cycle, loss of heat and cold.

1. Different forms of refrigeration:

In the actual cycle, there is a loss of pressure and temperature, and there will be flashing; And the theoretical cycle does not.

The theoretical cycle is the ideal refrigeration condition. The actual cycle process is energy-intensive.

2. The compression process is different

The theoretical cyclic evaporation process and the condensation process have no heat transfer temperature difference, both are isobaric processes, the compression process is an isentropic process, the throttling process isenthalpy process, and enter the expansion valve.

The condensation pressure of the saturated liquid enters the compressor and is the evaporation pressure of the saturated steam. Refrigerants.

Flows in pipes without friction loss.

The actual circulation, evaporation and condensation processes are present from the condenser.

The heat transfer temperature difference, entering the expansion valve is a supercooled liquid that leaves the evaporator.

And the compressor superheats the steam, the compressor is not an isentropic compression process, the entropy increases, and the throttling process is not an isenthalpy process, the specific enthalpy value.

will increase, there is friction loss and heat transfer loss in the refrigerant flow tube.

3. The laws are different:

The theoretical cycle follows the second law of thermodynamics.

Lawrs' Law, but the actual cycle, there is a loss of energy during the operation of the system, in other words, it is an open system. Compressor suction and discharge pressure and temperature. There are many errors compared to the theory. This has to do with the characteristics of the compressor.

Compared with the theoretical refrigeration cycle, the actual refrigeration cycle has "pressure loss", "compression gap volume", "cold and heat loss", etc., but the theoretical cycle is not taken into account.

The theoretical cyclic evaporation process and the condensation process have no heat transfer temperature difference and are isobaric processes, the compression process is an isentropic process, the throttling process is an isenthalpy process, the saturated liquid under the condensation pressure enters the expansion valve, and the saturated steam under the evaporation pressure enters the compressor. The refrigerant flows through the pipes without frictional loss.

In the actual cycle, there is a heat transfer temperature difference between the evaporation process and the condensation process, it is the supercooled liquid that leaves the condenser and enters the expansion valve, and the superheated steam leaves the evaporator and enters the compressor, the compression of the compressor is not an isentropic process, the entropy will increase, the throttling process is not an isenthalpy process, the specific enthalpy value will increase, and there is friction loss and heat transfer loss in the flow of refrigerant in the pipeline.

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The theoretical cycle is the ideal refrigeration condition. The actual cycle process is energy-intensive.

The actual refrigeration cycle is affected by the length, height and other reasons, which causes the effect of the machine to be inconsistent with the theory, and the theoretical refrigeration cycle is in a standard environment.

The actual refrigeration cycle is that during the operation of the machine, due to the influence of the temperature and environment of the internal and external worlds, the installation of the machine, the purity of Freon, the amount of injection, the quality of the evacuation, the length and height of the connecting pipe, etc., the effect of the machine is not as good as the effect calculated in the theory.

The theoretical refrigeration cycle is only theoretical, and the operation in a specific environment.

Introduction to the Refrigeration Cycle:

The refrigeration cycle consists of a compression process, a condensation process, an expansion process, and an evaporation process. It is to use a limited refrigerant in a closed refrigeration system to repeatedly compress, condense, expand, and evaporate the refrigerant, and continuously absorb heat and vaporize at the evaporator.

Refrigeration and cooling. The refrigeration cycle includes compression refrigeration cycle, absorption refrigeration cycle, adsorption refrigeration cycle, vapor injection refrigeration cycle and semiconductor refrigeration.

The actual refrigeration cycle is that during the operation of the machine, due to the influence of the temperature and environment of the internal and external worlds, the installation of the machine, the purity of Freon, the amount of injection, the evacuation and the replacement, the length and height of the connecting pipe, etc., the effect of the machine is not as good as the effect calculated in the theory, and the theoretical refrigeration cycle is only in theory, the working situation in a specific environment.

Compared with the theoretical refrigeration cycle, the actual refrigeration cycle has "pressure loss", "compression clearance volume", "cold and heat loss", etc., but the theoretical cycle is not considered.

To know the difference between the actual cycle and the theoretical cycle, you can understand it at a glance by referring to the enthalpy diagram.

The theoretical cycle follows the second law of thermodynamics, Lawx's law, but in practice it has energy loss in the operation of the system, that is, the system is an open system. The pressure temperature of the suction and discharge of the compressor. There are many errors compared to the theory. This is where the characteristics of the compressor come in.

The principle of the refrigeration cycle process is as follows: 1. The working principle of the refrigerator is in the circulation system of the refrigerator, the compressor sucks in the refrigerant vapor at low temperature and low pressure from the evaporator, compresses it into superheated steam at high temperature and high pressure through the compressor adiabatic compression, and then presses it into the condenser for constant pressure cooling, and releases heat to the cooling medium, and then cools it into supercooled liquid refrigerant. The liquid refrigerant becomes a low-pressure liquid refrigerant through the expansion valve adiabatic throttling, which evaporates and absorbs the heat in the air-conditioning circulating water (air) in the evaporator, so as to cool the air-conditioning circulating water to achieve the purpose of refrigeration, and the low-pressure refrigerant flowing out is sucked into the compressor, so that the cycle works.

Second, the structure of the refrigerator The refrigerator is composed of a compressor, a condenser, an evaporator, and a throttling device. Compressors are used to compress refrigerant vapor from low pressure to high pressure; The condenser cools the superheated vapor of the refrigerant discharged from the compressor and condenses into a refrigerant liquid, and the heat of the refrigerant is discharged to the cooling medium in the condenser. Precautions for Extended Data Chillers:

1. The closer the cold storage compressor is to the evaporator, the better, mainly easy to maintain, good heat dissipation, such as the installation of outdoor attention to rainproof, the four corners of the main engine need to be placed shockproof gaskets, horizontal installation firm, pay attention to safety is not easy to be touched. 2. Radiator installationThe closer the radiator installation position is to the host, the better, preferably in the upper position of the host, and the radiator installation position has the best heat dissipation environment. 3. Wire discharge: In addition to being tied with air conditioning ties, all wires need to be protected by corrugated hoses or wiring ducts.

4. The connection of the refrigeration system is due to the fact that the condenser and evaporator of the main engine have been pressed and sealed in the factory, so when opening, there should be pressure, and whether there is leakage.

The refrigeration cycle revolves around the basic properties of the refrigerant, which is achieved in this way:

The refrigeration system consists of a compressor, a condenser, a filter, a capillary, and an evaporator.

As we can see from the refrigeration cycle diagram, the refrigerant has a clear flow direction, from the exhaust port of the compressor, through the condenser, expansion valve, evaporator and back to the suction port of the compressor to complete a complete refrigeration cycle. During the refrigeration cycle, the key components are accompanied by changes in the pressure, temperature and phase of the refrigerant.

The evaporator of the refrigeration system absorbs a large amount of heat, so that the liquid refrigerant evaporates into a gaseous state at low pressure; The condenser releases a large amount of heat, which turns the gaseous refrigerant into a liquid state at high pressure. This is also the basic function and function of two vessels: the evaporator and the condenser.

The state of the refrigerant in the refrigeration cycle changes as follows:

The compressor absorbs the low-temperature and low-pressure gaseous refrigerant of the evaporator, compresses the refrigerant through the input of electric energy, discharges the high-temperature and high-pressure gaseous refrigerant, releases heat from the condenser to the surroundings, liquefies into medium-temperature and high-pressure liquid refrigerant, filters out impurities, and reduces the pressure by the throttling of the expansion valve (or capillary) to form a low-temperature and low-pressure liquid refrigerant. The low-temperature and low-liquid refrigerant enters the evaporator, absorbs a large amount of heat around, boils and vaporizes and evaporates into a low-temperature and low-pressure gaseous refrigerant, and the compressor absorbs and shrinks and discharges, and works in a circular manner.

It should be added that the evaporation of the refrigerant in the evaporator refers to the absorption of heat and boiling, because the boiling point of the refrigerant can be artificially controlled at a lower temperature under pressure control, so it is still a low temperature. For example, the evaporative boiling temperature of a household air conditioner is controlled at around +6 for cooling and -3°C for heating.

1. Direct cooling refrigeration type. The natural convection of the low temperature on the surface of the evaporator reduces the temperature in the chamber, but the temperature is uneven. It is relatively power-saving, and the effective volume is large under the same volume.

2. Air-cooled refrigeration. The cold air is forced into the space of the box by the air duct, resulting in circulation and uniform temperature. The freezer automatically defrosts the humidity is low, and the food is easy to dry and dehydrate, which is suitable for use in humid areas. The power consumption is higher than that of the direct cooling type, and the effective volume is small under the same volume.

3. Direct cooling and air-cooled refrigeration. It is a computerized temperature control double cycle system, which integrates air cooling and direct cooling refrigeration, and the refrigerator is frost-free, and the freshness effect is good. It makes full use of and concentrates the cooling capacity, directly sends cold to the cold room alone, sends cold to the air in the freezer, and is specially equipped with two dynamic cooling systems, intelligent double dynamic cooling, regardless of the cold room, the cold capacity of the freezer room is quickly and evenly sent to every corner, and the quick cooling and quick freezing and cooling are rapid.

How effective is the refrigeration circulation fan? What is the effect of a single refrigeration cycle? I suggest you don't buy this, it's okay when it's not hot, it's useless when it's hot, and it's damp, especially for the elderly.

A vapor compression refrigeration system consists of a compressor, a condenser, a capillary, and an evaporator, which are connected into a sealed system with pipes. The refrigerant liquid is heat exchanged with the cooled object at a low temperature in the evaporator, absorbs the heat of the cooled object and vaporizes, and the low-pressure steam generated is sucked in by the compressor and discharged at high pressure after compression. The high-pressure gaseous refrigerant discharged from the compressor enters the condenser, where it is cooled by cooling water or air at room temperature and condensed into a high-pressure liquid.

When the high-pressure liquid flows through the expansion valve, it throttles and becomes a low-pressure and low-temperature gas-liquid two-phase mixture, which enters the evaporator, in which the liquid refrigerant is evaporated and refrigerated, and the low-pressure steam produced is sucked in by the compressor again, and so on, and continues to circulate.

The theoretical cycle of refrigeration is mainly composed of four processes, namely, adiabatic compression process, isobaric condensation process, isoenthalpy throttling process, and isobaric endothermic process.

The theoretical cycle assumes:

The compression process is an isentropic process;

The throttling process is an isenthalpy process;

The pressure drop in the condenser is zero, the outlet is saturated liquid, the heat transfer temperature difference is zero, the pressure drop in the evaporator is zero, the outlet is saturated steam, and the heat transfer temperature difference is zero;

The working fluid remains unchanged in the pipeline state, and the pressure cooling difference is zero.

1) The theoretical cycle assumes that the compression process is an isentropic process; The throttling process is an isenthalpy process; The pressure drop in the condenser is zero, the outlet is saturated liquid, the heat transfer temperature difference is zero, the pressure drop in the evaporator is zero, the outlet is saturated steam, and the heat transfer temperature difference is zero; The working fluid remains unchanged in the pipeline state, and the pressure cooling difference is zero.

2) Difference: The actual compression process is a changeable process; The condenser outlet is a supercooled liquid; The evaporator outlet is superheated steam; In the process of condensation evaporation, there is a heat transfer temperature difference tk=t+δtk, to=t-δto

1. Principles of physical thermodynamics of refrigeration.

2. Medium (refrigerant).

The refrigerant should have: excellent thermodynamic properties; Excellent thermophysical properties; Good chemical stability; It has good miscibility with lubricating oil and is safe, economical and environmentally friendly.

3. Refrigeration cycle principle.

4. Basic structure composition (take chiller as an example).

As for the heating and cooling system, the heat exchanger is realized through the four-way valve switching: that is, the exchange of heat exchange states between the condenser and the evaporator, so as to achieve the purpose of cooling or heating.

5. The main components of the refrigeration system.

a. Compressor: provide power for the refrigerant cycle, and realize the compression of coolant gas in the refrigeration cycle process of compression, condensation (heat release), expansion and evaporation (heat absorption). Compressors generally include: reciprocating, scrolling, screw, and centrifugal.

b. Condenser: refrigeration cycle exothermic equipment, in the process of compression, condensation (exothermic), expansion and evaporation (endothermy) refrigeration cycle with the help of air or water, the high-temperature and high-pressure coolant gas pumped out of the compressor is condensed into medium-temperature and high-pressure liquid, and the heat is taken away with the help of air or water.

c. Expansion valve: The expansion valve enables the liquid refrigerant at medium temperature and high pressure to become wet steam at low temperature and low pressure through its throttling, and plays a role in controlling the flow of coolant to prevent the underutilization of the evaporator area and the phenomenon of knocking the cylinder. Throttle expansion devices generally include throttle pipes, throttle plates, and electronic expansion valves.

d. Evaporator: refrigeration cycle heat absorption equipment, in the process of compression, condensation (heat release), expansion and evaporation (heat absorption) in the refrigeration cycle process, the use of refrigerant evaporation and gasification to form a low temperature and low pressure gas process heat absorption, the cold medium (such as: air, water) to cool down to achieve the effect of refrigeration.

6. Common accessories for refrigeration system: such as filter driers, etc., the filter drier is mainly used to filter impurities, the inlet end is a coarse metal mesh, the outlet end is a fine metal mesh, and a molecular sieve with excellent hygroscopic characteristics is installed as a desiccant to absorb the moisture in the refrigerant. end

The different directions of refrigerant circulation in the pipelines of the air conditioning system determine the cooling or heating of the air conditioner.

When the four-way valve is in the refrigeration state, that is, the condenser is outdoors, the evaporator is indoor, the air conditioner is in the refrigeration state, and the heating is the opposite.

1. Refrigeration principle: the high-temperature and high-pressure refrigerant discharged from the compressor passes through the four-way valve (connected to the refrigeration state), and the direction of the flow of the high-temperature refrigerant discharged from the compressor is first dissipated from the outdoor condenser through the high-pressure pipe, and then throttled and depressurized through the capillary tube, enters the evaporator, discharges the cold air, and finally returns to the compressor through the oil absorber and low-pressure pipe.

Schematic diagram of air conditioning and refrigeration:

2. Heating principle: the high-temperature and high-pressure refrigerant discharged from the compressor passes through the four-way valve (connected heating mode), and the flow direction of the high-temperature refrigerant discharged from the compressor first blows warm air through the indoor evaporator (indoor unit), throttles and lowers the pressure through the capillary tube, enters the condenser of the outdoor unit, and finally returns to the compressor through the oil filter and low-pressure pipe.

Schematic diagram of air conditioner heating: