What can be cooked from squid: quick and tasty
Refrigeration 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 at the expense of the energy consumed in this case. The refrigeration unit is carried out according to the project, depending on project assignment, which determines the object to be cooled, the required range of cooling temperatures, energy sources and types of cooling medium (liquid or gaseous).
A refrigeration unit can consist of one or several refrigeration machines, complete with auxiliary equipment: a power and water supply system, instrumentation, regulation and control devices, as well as a heat exchange system with a cooled object. The refrigeration unit can be installed indoors, outdoors, in transport and in various devices in which it is necessary to maintain a predetermined lower temperature and remove excess moisture in the air.
The heat exchange system with the object to be cooled can be with direct cooling by a refrigerant, in a closed system, in an open system, as in cooling with dry ice, or with air in an air refrigerator. The closed loop system can also be with an intermediate refrigerant that transfers cold from refrigeration unit to the object to be cooled.
The beginning of the development of refrigeration engineering on a wide scale can be considered the creation by Karl Linde in 1874 of the first ammonia steam compressor refrigeration machine... Since then, many types 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 refrigerating machines: absorption refrigerating machines and steam jet; 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 field of application is selected. Chillers and plants are currently used in many areas National economy and at home.
2. Thermodynamic cycles of refrigeration units
The transfer of heat from a less heated source to a more heated source becomes possible in the case of organizing any compensating process. As a result, refrigeration cycles are always realized as a result of energy consumption.
In order for the heat removed from the "cold" source to be given to the "hot" source (usually ambient 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. As a result, plants operating on such 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 used working fluid and the principle of operation. Heat transfer from a "cold" source to a "hot" one can be carried out at the expense of work or heat costs.
2.1. Air refrigeration units
In air refrigeration units, air is used as a working medium, and the transfer of heat from a "cold" source to a "hot" one is carried out at the expense of mechanical energy. The decrease in air temperature necessary for cooling the refrigerating 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 carried out at the expense of internal energy, in connection with which the temperature of the working fluid drops. A diagram of an air refrigeration unit is shown in Figure 7.14.
Rice. fourteen. : HC - refrigerating chamber; K - compressor; TO - heat exchanger; D - expansion cylinder (expander)
The temperature of the air entering from the refrigerating 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 TO heat exchanger, its temperature at a constant pressure decreases - theoretically to the ambient temperature Tz. In this case, the air gives in environment heat q (J / kg). As a result, the specific volume of air reaches the 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) with the performance of useful work equivalent to a darkened area 3-5-6-4-3 , the air temperature drops below the temperature of the objects cooled in the refrigerator compartment. 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 objects to be cooled to the air. The quantity q 2, called the cooling capacity, is the amount of heat received by 1 kg of the working fluid from the objects to be cooled.
2.2. Steam compressor refrigeration units
In steam compressor refrigeration units (PCHU), low-boiling liquids are used as a working fluid (Table 1), which makes it possible to implement the processes of supply and removal of heat according to isotherms. For this, the processes of boiling and condensation of the working fluid (coolant) are used at constant values pressures.
Table 1.
In the XX century, various freons based on fluorochlorocarbons were widely used as refrigerants. They caused active destruction of the ozone layer, and therefore, their use is currently limited, and the main refrigerant used is the K-134A refrigerant (opened in 1992) based on ethane. Its thermodynamic properties are close to those of K-12 freon. Both refrigerants have insignificantly different molecular weights, heats of vaporization and boiling points, but, unlike K-12, the K-134A refrigerant is not aggressive towards the ozone layer of the Earth.
The PKHU scheme and the cycle in T-s coordinates are shown in Fig. 15 and 16. In PKKhU, the pressure and temperature are reduced by throttling the refrigerant as it flows through the pressure reducing valve РВ, the flow area of which can change.
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 KD, where it condenses at constant pressure and temperature values in the process 2-3. The released heat q1 is removed to the "hot" source, which in most cases is the ambient air. The formed condensate is throttled in a pressure reducing valve PB with a variable flow area, which allows changing 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 vapor compressor refrigeration unit: КД - capacitor; K - compressor; HC - refrigerating chamber; PB - pressure reducing valve
Since the throttling process proceeding at a constant enthalpy value (h3 - h) is irreversible, it is depicted by 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 refrigerating chamber, where, at constant pressure and temperature values, it evaporates due to the heat q2b taken from the objects in the chamber (process 4-1).
Rice. 16. : 1 - refrigerating chamber; 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 refrigerating chamber, in T-B-coordinates, is determined by the area of the rectangle under the isotherm 4-1.
The use of low-boiling liquids in PCHU as a working fluid makes it possible to approach the reverse Carnot cycle.
Instead of a throttling valve, an expansion cylinder can also 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 objects to be cooled will be greater - it will be determined by the area under the isotherm 5-4-1. Despite the partial compensation of the energy consumption for the compressor drive by 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, it is much easier to regulate the temperature in the refrigerating chamber in units with a variable section throttle.
Fig 17.
To do this, it is enough just to change the flow area of the throttling valve, which leads to a change in the pressure and the corresponding temperature of saturated refrigerant vapor at the outlet of the valve.
Currently, instead of reciprocating compressors, blade compressors are mainly used (Fig. 18). The fact that the ratio of the refrigerating coefficients of the PKHU and the reverse Carnot cycle
In real steam compressor installations, from the heat exchanger-evaporator of the refrigerating chamber, not wet, but dry or even superheated steam enters the compressor (Fig. 17). This increases the heat removed q2, reduces the rate of heat exchange of the refrigerant with the cylinder walls and improves the lubrication conditions for the compressor piston group. In a similar cycle, some overcooling of the working fluid occurs in the condenser (isobar section 4-5).
Rice. eighteen.
2.3. Steam jet refrigeration units
The cycle of a steam jet refrigeration unit (Fig. 19 and 20) is also carried out at the expense of the consumption of thermal, and not mechanical energy.
Rice. 19.: ХК - refrigerating chamber; E - ejector; КД - capacitor; РВ - pressure reducing valve; H - pump; KA - boiler unit
Rice. twenty.
In this case, the spontaneous transfer of heat from a more heated body to a less heated body is compensating. Steam of any liquid can be used as a working fluid. However, the cheapest and most readily available refrigerant is usually used - water vapor at low pressures and temperatures.
From the boiler plant, steam enters the nozzle of the ejector E. When the steam flows out at a high speed, a vacuum is created in the mixing chamber behind the nozzle, under the action of which the refrigerant is sucked into the mixing chamber from the refrigerating chamber HK. In the diffuser of the ejector, the speed of the mixture decreases, and the pressure and temperature rise. Then the vapor mixture enters the KD condenser, where it turns into a liquid as a result of the removal of heat q1 into the environment. Due to the multiple decrease in the specific volume during condensation, the pressure decreases to a value at which the saturation temperature is approximately equal to 20 ° C. One part of the condensate is pumped by the H pump into the KA boiler unit, and the other part is throttled in the PB valve, as a result of which wet steam with a slight degree of dryness is formed when pressure and temperature decrease. In the heat exchanger-evaporator HK, this steam is dried at a constant temperature, taking heat q2 from the objects being cooled, and then again enters the steam ejector.
Since the costs of mechanical energy for pumping the liquid phase in absorption and steam jet refrigeration units are extremely small, they are neglected, and the efficiency of such units is estimated by the heat utilization coefficient, which is the ratio of the heat taken from the objects to be cooled to the heat used to implement the cycles.
To obtain low temperatures as a result of heat transfer to the "hot" source, other principles can be used in principle. For example, the temperature can be lowered by evaporation of water. This principle is applied in hot and dry climates in evaporative air conditioners.
3. Household and industrial refrigerators
Refrigerator - a device that maintains a low temperature in a heat-insulated chamber. They are usually used for storing food and other items that require cold storage.
In fig. 21 shows a diagram of the operation of a single-compartment refrigerator, and Fig. 22 - the 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 that transfers heat from the working chamber of the refrigerator to the outside, where it is given 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 chambers for storing food and low-temperature freezers. Recently, however, the most widespread are two-compartment refrigerators that include both components.
Refrigerators are of 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 - a compressor that receives energy from the electrical network;
2 - condenser located outside the refrigerator;
3 - evaporator inside the refrigerator;
4 - thermostatic expansion valve (TRV), which is a throttling device;
5 - refrigerant (a substance circulating in the system with certain physical characteristics - usually freon).
3.1. Compression refrigerator working principle
The theoretical basis on which the principle of operation of refrigerators is built, the diagram of which is shown in Fig. 23, is the second law of thermodynamics. The cooling gas in refrigerators performs the so-called reverse Carnot cycle... In this case, the main transfer of heat is not based 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 at the same time, to achieve high performance, either a compressor that creates a very high pressure or a very large area of a cooling and heating heat exchanger is required.
The refrigerant enters the evaporator under pressure through the throttling orifice (capillary or expansion valve), where, due to a sharp decrease in pressure, evaporation liquid and turning it into steam. In this case, the refrigerant removes heat from the inner walls of the evaporator, due to which the inner space of the refrigerator is cooled. The compressor sucks in the refrigerant in the form of vapor from the evaporator, 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 down, giving off 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 high pressure condenses and turns into a liquid state, releasing heat, and in the evaporator under the influence low pressure the refrigerant boils and turns into gaseous, absorbing heat.
A thermostatic expansion valve (TRV) is required to create the required pressure difference between the condenser and the evaporator, at which the heat transfer cycle takes place. It allows you to correctly (most completely) fill the internal volume of the evaporator with boiled refrigerant. The throughput of the expansion valve changes as the heat load on the evaporator decreases, and as the temperature in the chamber decreases, the amount of circulating refrigerant decreases. The capillary is an analogue of the 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 switches on the compressor again.
3.2. Absorption refrigerator working principle
The absorption water-ammonia refrigerator uses the property of one of the widespread refrigerants - ammonia - to dissolve well in water (up to 1000 volumes of ammonia per 1 volume of water). The principle of operation of an absorption refrigeration unit is shown in Fig. 26, and her circuit diagram- in fig. 27.
Rice. 26.
Rice. 27.: GP - steam generator; КД - capacitor; РВ1, РВ2 - pressure reducing valves; HC - refrigerating chamber; Ab - absorber; H - 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 (stripper / generator) and there it is decomposed into ammonia and water by heating. Vapors of ammonia and water from it under pressure enter the separation device ( distillation column), where the ammonia vapor is separated from the water. Further, practically pure ammonia enters the condenser, where, after being cooled, it condenses and through the throttle again enters the evaporator for evaporation. Such a heat engine can use a variety of devices, including jet pumps, for pumping refrigerant solution, and does not have moving mechanical parts. In addition to ammonia and water, other vapors of substances can also be used - for example, a solution of lithium bromide, acetylene and acetone. The advantages of absorption refrigerators are quiet operation, no moving mechanical parts, the ability to work from heating by direct fuel combustion, the disadvantage is low refrigeration capacity per unit volume.
3.3. The principle of operation 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) when it is released at the other junction in the case of passing current through them. This principle is used, in particular, in cooler bags. It is possible to both decrease and increase the temperature using the 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 cooler is based on Peltier elements. It is silent, but it is not widely used due to the high cost of cooling thermoelectric elements. However, small automotive refrigerators and drinking water coolers are often manufactured with Peltier cooling.
3.4. The principle of operation of the refrigerator on vortex coolers
Cooling is carried out by expanding the air pre-compressed by the compressor in blocks of special vortex coolers. They are not widespread because of the high noise level, the need to supply compressed (up to 1.0-2.0 MPa) air and its very high flow rate, low efficiency. Advantages - great safety (no electricity is used, no moving parts and hazardous 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.
Fig 32.
Rice. 33.
For example, refrigeration units compressor-condensing (type AKK) or compressor-receiver (type AKR), shown in Fig. 34, are designed to operate with temperature maintenance 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.
The machine method is the most common way of obtaining cold by changing the state of aggregation of the working substance, boiling it at low temperatures, with the removal of the necessary heat of vaporization from the cooled body or medium.
One of the conditions for the effective operation of commercial refrigeration equipment is the use of refrigerating agents as working substances with good thermodynamic, thermophysical, physicochemical, physiological and ozone-safe properties. Cost and availability are also important. Refrigerating agents must not be poisonous, cause suffocation and irritation of the mucous membranes of the eyes, nose and respiratory tract of a person.
A distinction is made between natural and artificial refrigerants. Natural refrigerants include: ammonia (R717), air (R729), water (R718), carbon dioxide (R744), etc., artificial refrigerants - freons (mixtures of various freons).
There are currently three types of hydrofluorocarbon refrigerants:
chlorofluorocarbons (CFCs) with high ozone depletion potential. For example: R12, R13, R502, R503;
Hydrochlorofluorocarbons (HCFCs), which contain hydrogen atoms, resulting in a shorter lifetime of these refrigerants in the atmosphere than CFCs, such as R22;
hydrofluorocarbons (HFCs), which do not contain chlorine. They do not deplete the ozone layer of the Earth and have a short lifetime in the atmosphere. For example: R134A, R404A.
In this regard, the problem of using natural substances as refrigerants, and first of all ammonia, is most urgent now for manufacturers of refrigeration equipment. In Russia, the need for cold for stationary refrigerators is mainly provided by ammonia refrigeration units, since ammonia does not destroy the ozone layer, does not directly affect the global thermal effect, has excellent thermodynamic properties, has a high heat transfer coefficient during boiling and condensation, and production availability.
The negative properties of ammonia include toxicity, fire and explosion hazard, and a strong unpleasant odor. Any ammonia accident leads to serious consequences.
Compression refrigeration machines are mainly used in trade, which consist of the following main components: a compressor, an air-cooled condenser, a thermostatic expansion valve (TRV) and an evaporator. The refrigerating machine, in addition to the listed main parts, has automation devices, filters, dryers, heat exchangers, etc.
The compressor is the most complex and important part of the refrigeration machine. It serves for suction of refrigerant vapors from the evaporator, compression and discharge into the condenser. The main indicator of the compressor's operation is its refrigerating capacity (the amount of heat that the refrigerating machine receives per unit of time from the cooled medium).
An air cooled condenser is a heat exchanger in which the vaporous refrigerant coming from the compressor is converted into a liquid. This process takes place when the refrigerant gives off heat to the external environment.
An evaporator is a heat exchanger that removes heat from the medium to be cooled.
The thermostatic expansion valve is used to automatically supply the required amount of refrigerant to the evaporator. It controls and maintains the set temperature of the refrigerant vapor at the outlet from the evaporator.
Automation devices provide starting, stopping the refrigeration machine, protecting it from overloads, maintaining a given temperature regime in a cooled environment, optimal filling of the refrigerant evaporator, timely thawing of the snow coat from the evaporators.
The pressure switch automatically maintains the set suction pressure by turning the compressor on and off.
Receiver - a reservoir that collects liquid refrigerant in order to ensure its uniform flow to the expansion valve and to the evaporator. The filter serves to remove mechanical impurities. The dehumidifier is designed to absorb moisture from the refrigerant when filling the system with it and during machine operation. The heat exchanger serves to superheat the refrigerant vapors from the evaporator to the compressor and subcool the refrigerant from the condenser to the expansion valve.
The principle of operation of the refrigerating machine is as follows.
1. In the evaporator installed in the cooling volume, the liquid refrigerant boils at low pressure and temperature due to the extraction of heat from the environment.
2. From the evaporator, refrigerant vapors pass through the heat exchanger and the steam filter, then they are sucked out by the compressor, compressed and in the superheated state are pumped into the condenser, while the temperature and pressure increase.
3. In an air-cooled condenser, they condense; turn into liquid.
4. Liquid refrigerant flows down the condenser pipes and accumulates in the receiver, from where it passes under pressure through the liquid filter and heat exchanger.
5. The purified freon, passing through the narrow opening of the expansion valve, is throttled, sprayed and, with a sharp drop in temperature and pressure, enters the evaporator.
The cycle repeats itself. Circulating in such a closed circle, the refrigerant alternately changes its state of aggregation, that is, there is an abrupt transition of the refrigerant from a liquid to a gaseous state and vice versa.
Currently, commercial refrigeration equipment uses various refrigeration systems: built-in, remote and centralized.
Heat inflows into the sales areas of stores from refrigeration units built into the equipment lead to a decrease in turnover and an increase in unforeseen costs, including:
uncomfortable conditions for buyers are created ( heat air in the trading floor and high level noise, unpleasant odors);
uncomfortable conditions for sellers and service personnel lead to a decrease in the quality of service, the image of the enterprise falls and the turnover decreases;
the service life of built-in refrigeration units is 2 ... 3 times lower than when using external cooling systems, and 4 ... 6 times lower than when using central units;
frequent equipment failures occur;
there are additional costs for air conditioning and energy consumption.
The external refrigeration supply is a refrigeration supply system based on autonomous condensing units located in the engine room and isolated from the retail premises. Moreover, each unit can provide cold to several consumers.
One of the most important conditions for the effective development of trade enterprises is the use of centralized refrigeration supply systems, which are several parallel-connected compressors on a single frame with additional equipment. Each central unit is equipped with a microprocessor control unit that regulates the cooling capacity of the unit and ensures the uniform operation of each compressor and condenser.
The main advantages of using a centralized refrigeration system are as follows:
central units are compact and take up considerably less space;
significant energy savings are achieved, since large compressors have a higher ratio useful action;
for large supermarkets, a centralized refrigeration system is more economically profitable than the traditional refrigeration option; the turnover is increasing;
high reliability is ensured due to the use of several compressors;
in case of failure of one or more compressors, the remaining compressors will maintain the required temperature to prevent product loss until the malfunction is eliminated;
Cooling is subdivided into natural and artificial. Energy is not spent on the first. Moreover, the temperature of the object tends to the temperature of the surrounding air. Artificial cooling is a decrease in the temperature of an object to a level below the same indicator of the environment. Such cooling requires refrigeration machines or devices. They are usually used in industry to achieve the desired storage conditions, flow chemical reactions, security. Heat and refrigeration machines are very widely used in everyday life. Their principle of operation is based on the phenomena of sublimation and condensation.
Ice chilling
This is the most affordable and simple form of cooling. It is especially convenient in areas where there is a possibility of natural ice accumulation.
As a means of cooling, ice is used in the process of harvesting and storing fish, for short-term storage of vegetable products, transportation food products chilled. Ice is used in cellars and glaciers. In such equipment, thermal insulation is very important. In stationary glaciers, the walls are hydro- and thermally insulated. They are designed for a temperature range of +5 ... + 8 ° C.
Ice-salt cooling
The ice-salt cooling method makes it possible to maintain even lower temperature conditions in the volume to be cooled. Using ice and salt together makes it possible to lower the temperature at which ice melts. This is the principle. Refrigeration principle.
For this purpose, ice and sodium chloride are mixed. Depending on the salt concentration, the ice temperature ranges from -1.8 to -21.2 ° C.
The melting point reaches a minimum if the salt in the mixture is 23%. In this case, the ice does not melt at a minimum value.
Dry ice is used to maintain low temperatures during the storage of fruits, ice cream, vegetables, semi-finished products. This is the name for the solid state of carbon dioxide. At atmospheric pressure and heating, it turns from solid to gaseous, passing the liquid phase. The cold performance of dry ice is twice that of water ice. When dry ice is sublimated, carbon dioxide is produced, which, among other things, performs a preservative function, contributing to the preservation of food.
Cooling methods using ice also have a number of disadvantages that limit their application. In this regard, machine cooling becomes the main method of generating cold.
Artificial cooling
Machine cooling is the production of cold produced by refrigeration machines and installations. This method has several advantages:
- in automatic mode, a constant temperature level is maintained, which is different for different groups products;
- the cooled space is optimally used;
- it is convenient to operate the refrigerated premises;
- low maintenance costs.
How does it work
The principle of operation of the refrigeration machine is as follows. Of course, a person who only uses a refrigeration machine or is looking for it does not have to deeply and comprehensively understand the operation of refrigeration machines. At the same time, knowledge of the fundamental principles of the operation of such installations will not be at all superfluous. This information can help you make an informed choice of equipment and make it easier to talk with professionals when choosing refrigeration equipment.
It is also important to understand how the chiller works. In situations where refrigeration equipment fails and a specialist call is required, it makes sense to delve into the principle of operation of such machines. After all, understanding the specialist's explanations that you need to replace or repair any part of the refrigeration machine will allow you not to lose extra money.
The main principle of a refrigeration machine is to remove heat from an object being cooled and transfer it to another object. It is important to understand that heating or contraction of an object is accompanied by the transfer of energy to it, while cooling and expansion takes away energy. Heat transfer is based on this.
To transfer heat, refrigerators use refrigerants - special substances that take heat away from the object of cooling during boiling and expansion at a constant temperature. Subsequently, after compression, energy is transferred to the cooling medium through condensation.
Purpose of individual nodes
The compressor of the refrigeration machine ensures the circulation of the refrigerant in the system, its boiling in the evaporator with the injection into the condenser block.
It is designed to suck the refrigerant freon in a gaseous state from the evaporators, and, by compressing, pump it into the condenser, where it turns into a liquid. Then freon in a liquid state accumulates in the receiver. This unit is equipped with inlet and outlet shut-off valves. The further path of the refrigerant is from the receiver to the filter drier. Here, residual moisture and impurities are removed and fed to the evaporator.
In the evaporator, the refrigerant reaches a boil, which removes heat from the object to be cooled. Further, the refrigerant, already in a gaseous state, enters from the evaporator into the compressor, being cleaned through a filter from impurities. Further, the working cycle of the unit is repeated, this is the principle. Refrigeration principle.
Refrigeration unit
The combination of a set of parts and assemblies of a refrigeration machine on a single frame is usually called a refrigeration unit. The combination of the refrigeration machine units by the manufacturer makes the installation more convenient, and it happens faster.
The cooling capacity of such units is a parameter representing the amount of heat taken from the medium subjected to cooling in one hour. With different operating modes, the cold performance varies over a wide range. As the condensation temperature rises and the evaporation rate decreases, the performance decreases.
Refrigerants
Refrigerating machines used in trade organizations use freon or freon as refrigerants, and ammonia for freezing on an industrial scale.
Halon is a heavy colorless gas with a faint odor, perceptible only when its concentration in the air reaches 20%. The gas is not flammable or explosive. Lubricating oils are readily soluble in freon. At high temperatures, they form a homogeneous mixture with it. Freon does not affect the taste, aroma and color of products.
Refrigeration units with freon should not contain more than 0.006% of the mass of moisture. Otherwise, it will freeze in the thin tubes, interfering with the operation of the chiller. Due to the high fluidity of the gas, a good sealing of the units is required.
Ammonia is a colorless, pungent-smelling gas that is hazardous to human body... Its permissible content in the air is 0.02 mg / l. When the concentration reaches 16%, an explosion is possible. When the gas content is over 11% and an open flame nearby, combustion starts.
Today we cannot imagine our life without devices that cool food. Even in production, realize technological process impossible without refrigeration machines. So, it turns out that we need refrigeration units Everyday life, including production and trade.
It is not always possible to use natural cooling, given the seasonality and the ability to reduce the temperature to a maximum of air temperature, and in summer this is not at all realistic. And this is where our need for a refrigerator begins. based on the fact that with the help of technology to implement the evaporation process and generate condensate.
Among the advantages of refrigeration units, one can single out the automatic operation of maintaining a constant low temperature, which will be optimal for a specific category of products. But this concerns the actual benefits, and if we take into account the costs of operation, repair and Maintenance, then the refrigerator turns out to be a profitable technique.
The principle of operation of a chiller is based on cooling, a physical process based on the consumption of heat generated by the machine as a result of the boiling of a liquid. With what temperature indicator the liquid medium reaches a boil will depend on the origin of the liquid and the level of pressure exerted.
A high pressure reading means a high boiling point. Exactly in the same dependence this process works and vice versa: lower pressure - lower temperature of boiling and evaporation of the liquid.
The chemical properties of each type of liquid qualitatively affect the temperature required for boiling. So, for example, water boils at 100 degrees, and liquid nitrogen need -174 degrees Celsius.
Consider liquid freon. This refrigerant is the most popular substance with which the entire refrigeration system is saturated. By the way, freon under normal conditions in an open container can boil even at normal atmospheric pressure. Moreover, this process will begin immediately as soon as the freon comes into contact with air.
This phenomenon is certainly accompanied by the absorption of ambient heat. You will be able to observe how the vessel will become covered with frost, because condensation and freezing of water vapor in the air occurs. This action will end only when the refrigerant takes on a gaseous state, or the pressure above the freon does not increase in order to stop evaporation and stop the conversion of liquid freon into gaseous.
This is how a refrigeration machine works. in simple words ... A similar cycle is performed by liquid freon in the refrigerator system. The difference lies in the fact that the vessel is not open, but a special one that does not have access to air, called a heat exchanger unit, or, to be more precise, an evaporator.
The refrigerant boiling in the evaporator enters the active phase of absorbing heat emanating from the hose of the heat exchanger assembly. And the tubes, or rather their material, will be washed by liquid, and this is directly related to the air cooling process. Such a process should not be interrupted, it is permanent. To maintain it, it is necessary to regularly boil freon in the evaporator, which means constant removal of gaseous refrigerant and adding it in a liquid state.
Condensation of liquid freon vapor requires a temperature exactly what it will be, depending on atmospheric pressure. The higher the pressure reading, the higher the degree for condensation. A pressure of 23 atmospheres is necessary to condense the vapors of R22 freon, while the temperature will be +55 degrees.
Refrigerant vapors, when converted to liquid, give off a large amount of heat to the environment. The refrigerator for this process has a special, completely sealed heat exchanger, called a condenser. It is designed to remove the released heat energy. The capacitor looks like an aluminum element with a ribbed surface.
In order to remove freon vapors from the evaporator, and create a pressure that will be optimally favorable for condensation, a special pumping device is needed - a compressor. In addition, a refrigeration unit cannot do without the operation of the freon flow regulator. This function is assigned to the throttling capillary tube. Each of the elements of the refrigeration system is connected to each other by a pipeline, forming a sequential chain - this is how the system circle is closed.
The principle of operation of the refrigeration unit on freon
Assumes the execution of a real cycle, which is significantly different from the theoretical one. The difference lies in the presence of such a thing as pressure loss. This happens during a real cycle on the compressor valves (read more about the types of the compressor here :) and on its piping in particular. Such losses must be compensated later.
To do this, it is necessary to achieve an increase in the work of compression, which will reduce the effectiveness of the cycle. The essence of this parameter is the ratio of the power of the unit and the power required for the operation of the compressor. But how efficiently the installation works is a comparative parameter, which does not in any way affect the performance of the refrigerator.
The principle of operation of the refrigeration unit on freon for comparison: the efficiency of work is 3.5, that is, for 1 unit of electrical energy for this system, there are 3.5 units of cold that it produces. The efficiency of the machine will increase with the growth of this indicator.