The physical nature of heat and cold is the same, the difference is only in the speed of movement of molecules and an atom. In a more heated body, the speed of movement is greater than in a less heated one. When heat is supplied to the body, the movement increases; when heat is removed, it decreases. Thus, thermal energy is the internal energy of the movement of molecules and atoms.
Cooling the body is the removal of heat from it, accompanied by a decrease in temperature. The simplest way of cooling is heat exchange between the cooled body and the environment - outside air, river sea water, soil. But in this way, even with the most perfect heat exchange, the temperature of the cooled body can be lowered only to the ambient temperature. This cooling is called natural cooling. Cooling the body below ambient temperature is called artificial. For it, they mainly use latent heat, absorbed by bodies when their state of aggregation changes.
The amount of heat or cold is measured in calories or kilogram-calories (kilocalories). A calorie is the amount of heat required to heat 1 g of water per 1 at normal atmospheric pressure, a kilocalorie is required to heat 1 kg of water at 1C under the same conditions.
There are several ways to obtain artificial cold. The simplest of these is cooling with ice or snow, the melting of which is accompanied by the absorption of a fairly large amount of heat. If heat gains from the outside are small, and the heat transfer surface of ice or snow is relatively large, then the temperature in the room can be reduced to almost 0 ° C. Practically in a room cooled by ice or snow, the air temperature can be maintained only at the level of 5-8 ° C. Ice cooling uses water ice or solid carbon dioxide (dry ice).
When cooled with water ice, there is a change in its state of aggregation - melting (melting). The cooling capacity, or the cooling capacity of pure water ice, is called the specific heat of fusion. It is equal to 335 kJ / kg. The heat capacity of ice is 2.1 kJ / kg degree.
Water ice is used for cooling and seasonal storage of food products, vegetables, fruits in climatic zones with a long cold period, where it can be easily prepared in natural conditions in winter.
Water ice is used as a cooling agent in special glaciers and ice storage facilities. There are glaciers with bottom loading of ice (glacier-cellar) and with side - pocket type.
Ice cooling has significant drawbacks: the storage temperature is limited by the ice melting temperature (usually the air temperature in ice warehouses is 5-8 ° C), it is necessary to put enough ice into the glacier for the entire storage period and add it as needed; significant labor costs for the preparation and storage of water ice; large dimensions of the ice storage room, approximately 3 times the size of the food storage room; significant labor costs for compliance with the necessary requirements for the storage of food products and the removal of melt water.
Ice-salt cooling is performed using crushed water ice and salt. By adding salt, the rate of ice melting increases and the temperature at which the ice melts is lowered. This is because the addition of salt causes a weakening of molecular cohesion and destruction of the ice crystal lattices. The melting of the ice-salt mixture proceeds with the extraction of heat from the environment, as a result of which the ambient air cools and its temperature decreases. With an increase in the salt content in the ice-salt mixture, its melting point decreases. The salt solution with the lowest melting temperature is called eutectic, and its melting temperature is called the cryohydrate point. The cryohydrate point for an ice-salt mixture with table salt is -21.2 ° C, with a salt concentration in the solution of 23.1% with respect to the total mass of the mixture, which is approximately equal to 30 kg of salt per 100 kg of ice. With further salt concentration, there is not a decrease in the melting temperature of the ice-salt mixture, but an increase in the melting temperature (at a 25% salt concentration in the solution to the total mass, the melting temperature rises to -8 ° C).
When an aqueous solution of common salt is frozen at a concentration corresponding to the cryohydrate point, a homogeneous mixture of ice crystals and salt is obtained, which is called a eutectic solid solution.
The melting point of the eutectic solid solution of sodium chloride is -21.2 ° C, and the heat of fusion is 236 kJ / kg. The eutectic solution is used for zerotor cooling. To do this, a eutectic solution of table salt is poured into zeroty - tightly sealed forms - and they are frozen. Frozen grains are used to cool counters, cabinets, refrigerated portable cooler bags, etc. In the trade, ice-salt cooling was widely used before the mass production of equipment with a machine cooling method.
Cooling with dry ice is based on the property of solid carbon dioxide to sublimate, that is, when heat is absorbed, it passes from a solid state to a gaseous state, bypassing the liquid state. The physical properties of dry ice are as follows: the sublimation temperature at atmospheric pressure is 78.9 ° C, the heat of sublimation is 574.6 kJ / kg.
Dry ice has the following advantages over water ice:
A lower temperature can be obtained;
The cooling effect of 1 kg of dry ice is almost 2 times that of 1 kg of water ice:
When cooled, no dampness occurs, in addition, when dry ice is sublimated, gaseous carbon dioxide is formed, which is a preservative that contributes to better preservation of products.
Dry ice is used for transportation of frozen products, cooling of packaged ice cream, frozen fruits and vegetables.
Artificial cooling can also be achieved by mixing ice or snow with diluted acids. For example, a mixture of 7 parts of snow or ice and 4 parts of diluted nitric acid has a temperature of -35 ° C. Low temperatures can also be obtained by dissolving salts in dilute acids. So, if 5 parts of ammonium nitrate and 6 parts of sodium sulfate are dissolved in 4 parts of diluted nitric acid, then the mixture will have a temperature of -40 ° C.
Obtaining artificial cold with the help of snow or ice, as well as with the help of cooling mixtures, has significant drawbacks: the laboriousness of the processes of harvesting ice or snow, their delivery, the difficulty of automatic regulation, and limited temperature capabilities.
Recently, in connection with the energy crisis, environmental pollution, the problem of using non-traditional, environmentally friendly methods of obtaining cold for the refrigeration processing of food products has become more and more urgent. The most promising of them is the cryogenic method based on liquid and gaseous nitrogen with the use of a machineless flow-through cooling system, which provides for a one-time use of a cryoagent.
The prospects of this method of refrigeration supply are increasing in connection with the discovery in Russia of large reserves (340 billion m 3) of underground high-nitrogen gases. The prime cost of purified nitrogen is an order of magnitude lower than nitrogen obtained using the air separation method.
Machineless flow-through nitrogen cooling systems have significant advantages: they are very reliable in operation and have a high freezing rate, which ensures almost complete preservation of the quality and appearance of the product, as well as minimal loss of its weight due to shrinkage.
The ecological purity of such systems should be especially noted (the Earth's atmosphere contains up to 78% of gaseous nitrogen).
The most common and operationally convenient cooling method is machine cooling.
Machine cooling is a method of obtaining cold by changing the aggregate state of the refrigerant, boiling it at low temperatures with the removal of the necessary heat of vaporization from the cooled body or medium
For the subsequent condensation of refrigerant vapors, a preliminary increase in their pressure and temperature is required.
The machine cooling method can also be based on the adiabatic (without heat supply and removal) expansion of the compressed gas. When the compressed gas expands, its temperature drops significantly, since the external work in this case is performed due to the internal energy of the gas. The operation of air chillers is based on this principle.
Cooling by expanding compressed gas, in particular air, is different from all cooling methods. At the same time, the air does not change its state of aggregation, like ice, mixtures and freon, it only heats up, perceiving the heat of the environment (from the cooled body).
The widespread use of machine cooling in trade is explained by a number of its operational properties and economic advantages. Stable and easily adjustable temperature conditions, automatic operation of the refrigeration machine without large expenditures of labor for maintenance, better sanitary and hygienic conditions for storing food, compactness and overall efficiency determine the advisability of using machine cooling.
At the enterprises of wholesale and retail trade, steam refrigeration machines are mainly used, the action of which is based on boiling at low temperatures of special working substances - refrigerants Steam refrigeration machines are divided into compression, in which refrigerant vapors are compressed in a compressor with the expenditure of mechanical energy, and absorption, in which refrigerant vapors are absorbed by the absorbent.
The device and principle of operation of the compression refrigeration machine. Compression refrigeration machine (Fig. 3.1) consists of the following main units: evaporator, compressor, condenser, receiver, filter, thermostatic valve. The automatic operation of the machine is ensured by a thermostatic valve and a pressure regulator. The auxiliary devices that contribute to the increase in the efficiency and reliability of the machine include: receiver, filter, heat exchanger, dehumidifier. The machine is driven by an electric motor.
The evaporator is a cooling battery that absorbs the heat of the environment due to the refrigerant boiling in it at a low temperature. Depending on the type of medium to be cooled, evaporators are distinguished for cooling liquid and air.
Rice. Compression refrigeration machine diagram:
1 - compressor; 2 - capacitor; 3 - receiver; 4 - filter; 5 -
thermostatic valve; 6 - evaporator; 7 - cooled
camera; 8 - electric motor; 9 - magnetic starter; ten -
push button switch; 11 - pressure switch
The compressor is designed to suck refrigerant vapors from the evaporator, compress them and pump them in a superheated state into the condenser. Piston and rotary compressors are used in small refrigeration machines, with reciprocating ones being the most widespread.
Condenser is a heat exchanger used to liquefy refrigerant vapors by cooling them. By the type of cooling medium, condensers are produced with water and air cooling. Condensers with forced air movement have vertically arranged flat coils made of copper or steel finned tubes. Natural air cooling is used only in refrigeration machines for household electric refrigerators. Water-cooled condensers are of shell-and-shell type and shell-and-tube type.
Receiver - a reservoir used to collect liquid refrigerant in order to ensure its uniform flow to the thermostatic valve and into the evaporator. In small freon machines, the receiver is designed to collect refrigerant during repairs of the machine.
The filter consists of copper or brass mesh and cloth gaskets. It serves to clean the system and the coolant of the agent from mechanical impurities formed as a result of insufficient cleaning during manufacture, installation and repair. Filters are liquid and steam. A liquid filter is installed after the receiver in front of the thermostatic valve, and a steam filter is installed on the compressor suction line.
To prevent rust and mechanical particles from entering the cylinders of small freon refrigerating machines, a filter in the form of a brass mesh cup is inserted into the suction cavity of the compressor.
The thermostatic expansion valve ensures a uniform flow of refrigerant into the evaporator, atomizes the liquid refrigerant, thereby reducing the condensing pressure to the evaporating pressure.
The efficiency of the refrigeration machine largely depends on the correct adjustment of the thermostatic valve. An excess of liquid refrigerant in the evaporator due to the wet running of the compressor can lead to water hammer. In case of insufficient filling of the evaporator with liquid, part of its surface is not used, which leads to a violation of the normal operation of the machine and a decrease in the evaporation temperature of the refrigerant.
The pressure regulator consists of a pressure switch (low pressure regulator) and a pressure controller (high pressure switch). To adjust the temperature regime within certain limits, it is necessary that the refrigerating capacity of the chiller always exceeds the heat input to it. Therefore, under normal conditions, there is no need for continuous operation of the chiller.
Periodic switching on of the refrigerating machine is carried out automatically by the pressure switch. The required temperature regime is achieved by regulating the duration of the breaks in the operation of the refrigerating machine. The pressure controller serves to protect against excessive pressure build-up in the discharge line. When the pressure in the condenser rises above 10 atm. (the norm is 6-8 atm.) it opens the circuit of the coil of the magnetic starter, the power supply to the electric motor is turned off and the refrigerating machine stops.
The refrigeration machine operates as follows. A highly volatile liquid (freon-12) enters the evaporator through a thermostatic valve. When exposed to low pressure conditions, it boils, turning into steam, and at the same time removes heat from the air surrounding the evaporator.
From the evaporator, freon vapors are sucked off by the compressor, liquefied and, in a superheated state from compression, are pumped into the condenser. In a water- or air-cooled condenser, they turn into liquid. Liquid freon flows down the condenser pipes and accumulates in the receiver, from where it passes through the filter under pressure, where mechanical impurities (sand, scale, etc.) are retained.
The freon purified from impurities, passing through a narrow (the opening of the thermostatic valve, throttles (crumples), atomizes and, with a sharp decrease in pressure and temperature, enters the evaporator, after which the cycle is repeated.
The working cycle of the refrigerating machine, taking into account the interaction of automation devices, is as follows. When the electric motor is off, the pressure switch contacts are open, the thermostatic valve does not let the liquid freon from the condenser into the evaporator, since the needle has fully entered the saddle and tightly closed the flow area. At this time, the evaporator continues the process of boiling the liquid refrigerant remaining after the machine is turned off. Due to the influx of external heat, the temperature of the evaporator gradually increases and, consequently, the pressure of the vapors accumulated in it increases. The pressure in the evaporator will rise until the pressure switch of the pressure switch closes the contacts and the machine starts to work.
When the machine is turned on, the suction of superheated vapors from the evaporator to the compressor begins. This results in an increase in temperature and pressure in the sensitive thermoregulatory valve cartridge, as a result of which the needle valve opens the bore. The liquid refrigerant, boiling intensively, rushes into the evaporator pipes. Boiling is accompanied by a significant decrease in the temperature of the vapor-liquid mixture, as a result of which the walls of the evaporator, the air surrounding it, and perishable foodstuffs are cooled.
A decrease in the ambient temperature reduces the amount of heat gain, Boiling becomes less intense, the amount of steam decreases, the pressure in the evaporator drops to the limit at which the pressure switch opens the contacts and the machine stops. By the time the machine is turned off, the supply of liquid refrigerant to the evaporator is reduced, since an excess of refrigerant entering it leads to a decrease in the temperature of the leaving vapors and to the automatic closing of the needle valve of the thermostatic expansion valve. A few seconds after stopping the machine, the pressure in the thermocylinder and the evaporator is finally equalized and the needle valve closes.
Refrigerants. Refrigerants are the working substances of steam refrigeration machines, with the help of which low temperatures are obtained. The most common of these are freon and ammonia.
When choosing a refrigerant, they are guided by its thermodynamic, thermophysical, physicochemical and physiological properties. Cost and availability are also important. Refrigerants should not be poisonous, should not cause suffocation and irritation of the mucous membranes of the eyes, nose and respiratory tract of a person.
Freon-12 (R-12) has the chemical formula CHF 2 C1 2 (difluorodichloromethane). It is a gaseous colorless substance with a weak specific odor, which begins to be felt when the volumetric content of its vapors in the air is over 20%. Freon-12 has good thermodynamic properties
Freon-22 (R-22), or difluoromonochloromethane (CHF 2 C1), as well as freon-12, has good thermodynamic and operational properties. It differs by a lower boiling point and a higher heat of vaporization. The volumetric refrigerating capacity of Freon-22 is approximately 1.6 times that of Freon-12.
Ammonia (NH 3) is a colorless gas with a suffocating strong characteristic odor. Ammonia has a fairly high volumetric refrigeration capacity. Its production is based mainly on the method of combining hydrogen with nitrogen at high pressure with the presence of a catalyst. Ammonia is also used to obtain low temperatures (down to -70 ° C) under high vacuum. The heat of vaporization, heat capacity and thermal conductivity coefficient of ammonia is higher, and the viscosity of the liquid is lower than that of freons. Therefore, it has a high heat transfer coefficient. The cost of ammonia is low compared to other refrigerants
As you know, some refrigerants have ozone-depleting properties, which cannot but be of concern to the international community.
The ability of chlorine-containing refrigerants to cause this process is called ozone depleting potential - ODP (Figure 3 2)
Rice. Ozone Depletion Potential
The ability of various substances to cause global warming processes is called the global warming potential - GWP (Figure 3.3)
Rice. Global warming potential
The lifespan of refrigerants in the atmosphere is also a very important factor.This is an indicator of the time during which various substances are stored in the atmosphere and can affect the environment In other words, the longer a chemical or freon is stored in the atmosphere, the less environmentally friendly it is (Figure 3-4)
Rice. Lifetime of refrigerants in the atmosphere
In 1985, the Convention for the Protection of the Ozone Layer was adopted in Vienna. It was joined by 127 states, including Russia and the CIS countries.
In 1989, the Montreal Protocol came into force on the gradual reduction, and then on the complete cessation in 2030 of the release of ozone-depleting refrigerants. Freons R-11, R-12, R-113, R-114, R-115, R-12B1, R-13B1, R-114B2 were classified as dangerous groups. In the 90s. the text of the protocol was strengthened by imposing restrictions not only on the production, but also on the trade, export and import of any refrigeration equipment containing ozone-depleting substances.
The Russian Federation has assumed the obligations arising from the Montreal Protocol for the Protection of the Ozone Layer. According to the decisions taken, R-502 has been banned for production since January 1, 1996. More distant terms have been set for R-22 - a reduction in production and use since 2005 and a complete ban since 2020.
To replace R-502 and R-22, the world's major manufacturers of chemical products have developed and are producing transitional (containing chlorofluorocarbons) and ozone-safe (consisting only of hydrofluorocarbons) refrigerant mixtures.
Transition refrigerants include R-402, R-403B and R-408A, which can be used in existing equipment. Most of these new working substances have appeared on the Russian market today.
Ozone-safe refrigerants R-507, R-404A, R-134A can be recommended both for work in new equipment and for reconstruction of low-temperature refrigeration systems. They are designed to replace R-22 in current and existing equipment.
For manufacturers, it is becoming more and more difficult to rationally select the refrigerant in relation to a specific facility. Therefore, the problem of using natural substances as refrigerants, and first of all ammonia, is most urgent now for manufacturers of refrigeration equipment.
Ammonia refrigeration units have been in operation for about 120 years. In Russia, the overwhelming part of the cold demand for stationary refrigerators is provided by ammonia refrigeration units.
In the 90s. and in Western Europe, the use of ammonia has increased significantly because it:
Does not deplete the ozone layer,
Does not directly affect the global thermal effect;
Possesses excellent thermodynamic properties;
Has a high coefficient of heat transfer during boiling and condensation;
Has a high energy efficiency in the refrigeration cycle;
It has a low cost, its production is affordable, the problems of its flammability and toxicity are solvable today, which makes it attractive for manufacturers of refrigeration equipment.
Refrigerating machines and units. A refrigeration machine is a set of mechanisms, apparatus and devices connected in series to form an artificial cold production system. Compact, constructive combinations of individual or all elements of a refrigeration machine are called a refrigeration unit.
By the type of refrigerant used, ammonia and freon refrigeration units are distinguished. According to the design features of the compressors, the units are divided into open and hermetic, and the condensers - with air and water cooling.
Depending on the composition of the elements included in them, refrigeration units are compressor, compressor-condensing, evaporative-regulating, evaporative-condensing and complex units. At trade enterprises, compressor-condensing units are used and, when cooled with a heat carrier, evaporative-control units are used.
The condensing unit consists of a compressor, a condenser (air or water cooling), an electric motor, automation devices and auxiliary devices (receivers, dryers, heat exchangers, etc.). An evaporator-regulating unit is a structural connection of the evaporator, auxiliary equipment, control station and automation devices. Complex units include all elements of the refrigeration machine.
Refrigerating machines are supplied separately and complete with commercial refrigeration equipment. The set of equipment includes a built-in evaporative battery and a built-in or separately packaged refrigeration unit. If the unit is to be installed outside the equipment, the mounting copper tubing must be included.
To cool the collection chambers, cabinets, counters and showcases, freon refrigeration units with a cooling capacity of up to 3 thousand kcal / h are used. These are mainly compressor-condensing units, pa6otaying on freon-12 and freon-22. Depending on the location of the electric motor and the method of transferring mechanical energy, open-type units are distinguished, as well as sealed ones.
In open-type units, the electric motor is mounted separately from the compressor, and the transmission of mechanical energy is carried out by a pulley-belt mechanism.
Sealed refrigeration units are the most promising. The tightness of the system is achieved through the use of a welded casing, a reduction in the number of detachable connections and the use of a thermostat instead of a pressure switch. Compared to open-type units, hermetic ones have significant advantages.
By combining the electric motor and compressor into a unit with a single eccentric shaft, there is no need for a Transmission Mechanism. This made it possible to reduce the mass and dimensions of the compressor and the unit, and to increase the shaft rotation speed up to 3 thousand rpm.
In a sealed unit, due to the reduction in the number of detachable joints, the absence of oil seals, the leakage of freon decreased, which made it possible to reduce its working stock in the system. The operating consumption of the refrigerant has also decreased, since the need for periodic refueling of cars has disappeared.
Cooling of the electric motor winding with a flow of sucked freon vapors made it possible to increase the load on the electric motor, reduce its parameters, power, dimensions and weight. For example, with an equal cooling capacity, the rated power of the electric motor of a sealed unit is 40% less than that of an open unit. As a result, power consumption is significantly reduced.
Sealed units have an important quality for shops, especially sales areas - a relatively low level of noise emitted. Reducing the size of the units makes it possible to more efficiently use the warehouse sales area, as well as the capacity of commercial refrigeration equipment.
The purpose and principle of operation of individual elements of sealed machines is somewhat different from open-type machines. The automatic control of the operation of a sealed refrigeration machine is carried out not by the pressure switch of the pressure switch), but by the thermostat (temperature switch). The overheating protection of the electric motor and overpressure of the condenser is ensured by the compressor thermal relay.
Below is a description of the main units of refrigeration machines.
Refrigerating units ACL 88TN (Fig. 35) and ACP 12TN, made on the basis of licensed compressors from Electrolux, have a small size and low noise level. They are intended for installation in commercial refrigeration equipment, both domestic and imported.
Rice. Refrigeration unit ACL 88TN
Refrigerating units ВС 4000 (2) and ВН 2000 (2) are units with scroll compressors manufactured by Copeland (Fig. 36).
The use of a scroll compressor has significantly increased the reliability of the product, both in comparison with hermetic reciprocating and open-type compressors. The scroll compressor has no valves and, if properly operated, cannot jam.
The VN 2000 refrigeration unit (2) is used in low-temperature chambers with a volume of 12-14 m, where it can provide temperatures up to -18 C.
Refrigerating unit ВС 4000 (2) is designed for cooling medium-temperature chambers with a volume of 24-30 m 3. Technical characteristics of refrigerating units are given in table.
Rice. Refrigeration unit ВС 4000 (2)
Condensing units of the SM MX series with a hermetic and semi-hermetic compressor Fig. 3 7), having an internal protection of the electric motor, an electrical control panel, protected from the external environment, can be installed outdoors, on the street.
Refrigeration Units Specifications
| VN 2000 (2) | BC 4000 (2) | ACI 88 IN | ACP12TN | |
| Refrigerant | R22 | R22 | R22 | R22 |
| Refrigerant boiling point range, ° С | -45 -15 | -25 -5 | -25 -5 | -25 -5 |
| Ambient temperature, ° С | +5 +45 | +5 +45 | +5 +45 | +5 +45 |
| Cooling capacity at a boiling point of the refrigerant 15 ° С (for VN 2000 (2) at -35 ° С) and an ambient temperature of 20 ° С, W | 2010 | 4360 | 600 | 800 |
| Compressor | ZF09K4E Sooreland | ZS21K4E Sooreland | L88TN Electrolux | P12TN Electrolux |
| Electric motor voltage, V. speed rpm | 380 3000 | 380 3000 | 220 3000 | 220 3000 |
| Dimensions, mm | 860x560x610 | 860x560x610 | 440x380x255 | 440x380x255 |
| Macca, kg | 90 | 90 | 30 | 30 |
Mounted in a soundproof galvanized steel casing. The equipment of the SM and MX series creates and maintains temperatures from 5 to -30 C.
The units effectively operate in refrigeration chambers in commercial enterprises, and are also widely used for cooling storage facilities.
The monoblock (Fig. 3 8) is a single unit that includes a hermetic compressor, air condenser, air cooler and electronic control panel. The monoblock is installed on prefabricated refrigerating chambers with a wall thickness of no more than 120 mm, by mounting it in the opening of the chamber panel on the wall or ceiling.
Rice. Condensing unit
Figure 3 8. Monoblock
The split system (Fig. 3.9) is a fully equipped refrigeration equipment, consisting of two separate parts. It is used to cool stationary refrigerating chambers.
Rice. Split system
The automation system ensures that the required temperature is maintained in the refrigerating chamber, protection against emergency modes and periodic defrosting of the air cooler.
All equipment is supplied with protection monitors that monitor the mains voltage.
Operates from a network with a voltage of 220 or 380 V, keeps cold at an ambient temperature of up to 45 ° C,
The world's largest manufacturer of compressors with refrigerating capacities from 1 to 173 kW for commercial refrigeration equipment, air conditioning, heat pumps is Copeland.
Copeland hermetic reciprocating compressors are manufactured according to specifications that ensure their use in any climatic zone of the world, which is achieved due to a wide range of operating voltages of electric motors. These compressors are manufactured to operate on certified refrigerants and high-quality lubricating oils from well-known world companies in high temperature (above 0 ° C), medium temperature (from 0 ° C to -15 ° C) and low temperature (from -15 ° C to -20 ° C) modes.
With the introduction of hermetic compressors, a new range of air-cooled condensing units has also appeared. This new nomenclature, with many features, both standard and customer-requested, is designed to work with the environmentally friendly refrigerants R-22 and R-134A. It has a wide performance range and high energy efficiency. All units [have a quiet and smooth running.
There are two main ranges of units available. The HAN range with conventional capacitor size is used to ensure:
Standard storage mode, when the temperature of the product being pledged is no more than 10 ° C higher than the temperature set in the storage;
Compactness and low cost;
Operation in conditions of normal ambient temperature.
The HAL range with a more powerful capacitor is used when:
The magnitude of the load on the unit often and dramatically changes over time (with periodic loading of large quantities of product at the same time or the need for rapid cooling of products, for example, milk);
It is necessary to achieve high energy efficiency, which ensures low operating costs;
Work to be done in an elevated ambient temperature.
Salonless refrigeration compressors "Copland" combine the latest design developments with the advantages of the latest refrigerants. Sealless compressors have high performance, long service life and a wide range of applications (high, medium and low temperature operation).
Models DLH, D6C, Discus, as well as two-stage compressors have connection devices for a mechanical differential oil pressure switch or an electronic sensor for the Sentronic oil pressure protection system.
All sealless compressors are direct-on-line capable. It is also possible to equip electric motors with switching the electric circuit from "star" to "delta" at start-up or using a part of the winding to reduce the starting current. For optimum no-load starting conditions, a dedicated device can be fitted on all Discus models as well as DLH models.
Each compressor is equipped with a motor protection device. A thermal overload relay is installed in single-phase motors. In three-phase motors, thermistors are built into the motor winding.
Capacity control equipment can be applied to all single stage 3-, 4-, 6- and 8-cylinder compressors. For D3D compressors, the Moduload load changing system has been developed with an especially low power consumption.
For ultra-low temperature applications, the Discus models with Demand Cooling should be used to regulate the compressor discharge temperature by injecting small amounts of liquid refrigerant into the compressor. The Demand Cooling system makes a single stage compressor a good alternative to a two stage compressor. In the case when the boiling point of the refrigerant, depending on the need, must change significantly (for example, from -50 ° C to -20 ° C), the Demand Cooling system becomes more cost-effective.
Copland also manufactures twin (TWIN) compressors. Twin compressors are available for all 2-stage and Discus models except those with Demand Cooling. The main advantages of tandem compressors are: double cooling capacity, reduced 50% modulation of cooling capacity and high efficiency even at partial load.
Air-cooled condensing units are produced on the basis of most models of sealless compressors. They are supplied filled with oil, fully equipped with automation and ready to go. Additionally, at the request of the customer, it is possible to install in them: crankcase heaters, a fan speed controller (for regulating the condensation temperature), a protective casing for outdoor installation, various modifications of the receiver in terms of capacity.
The Copeland matched scroll compressor is one of the most advanced hermetic compressors for air conditioning, medium temperature refrigeration and heat pump applications. The operating boiling temperature range of the scroll compressor is from positive to -20 ° C.
Compared to hermetic reciprocating or sealless compressors, scroll compressors have such significant advantages as:
High reliability and increased service life due to fewer refrigerant compression parts;
Overload resistance;
Low noise level due to the absence of valves and reciprocating movement of parts, as well as a high degree of consistency of movement of parts thanks to the patented "Compliance" principle;
Higher coefficient of refrigerant supply due to the absence of "dead" space;
Low vibration due to smooth, continuous compression;
Increased productivity, stability of the compressor when mechanical impurities, wear products or liquid refrigerant enters the compression zone;
Low starting torque and starting currents (no-load starting), for single-phase models there is no need for starting equipment;
Compactness and light weight.
The coefficient of performance of a scroll compressor when operating in standard European air conditioning mode reaches 3.37 W versus 2.75 - 2.95 W for a hermetically sealed reciprocating compressor.
A low-temperature scroll compressor of the Glacier type has appeared on the equipment market, which effectively and reliably operates at large pressure drops.It can operate on R-22, R-404A, R-507, R-134A refrigerants at boiling temperatures down to -45 ° C.
All types of Copland compressors are supplied filled with mineral oil for operation R-22 or polyester oil for operation on ozone-safe refrigerants or on R-22.
Scroll compressors (Fig. 3.10) are intended for use in air conditioners in industrial, commercial and office buildings.
On the market of climatic equipment, the products of the Maneurop company are in special demand. Its Performer brand compressors, thanks to their low noise level and high degree of reliability, satisfy all the requirements of the operation and the needs of the consumer.
By installing the compressors in pairs, three or four in a row, it is possible to achieve a cooling system capacity of up to 180 kW.
A distinctive feature of Performer compressors is the movable contact between the scrolls, which, using two patented floating seals, ensures perfect axial tightness and reduces stress and deformation.
High precision and state-of-the-art machining technologies prove that a simple oil film is what is needed to accurately seal the ends of the spiral, reduce contact between moving parts, minimize friction between them, increase volumetric efficiency and reduce vibration, which guarantees high performance. compressor and lengthens its service life.
Rice. Scroll compressor Performer from Maneurop
The advantages of Regformer scroll compressors are:
Higher efficiency. Controlled rotating parts with floating seals and improved spiral geometry;
Minimum noise level. Effective compressor balancing system and vibration protection;
Increased reliability. Longer service life due to the absence of friction between the scrolls and cooling of the engine with the suction refrigerant;
Easy to install. Most models use braze or union nut nipples as standard connections. Reverse rotation protection devices, as well as protection of the electric motor itself, are an integral part of the design. No additional accessories are required when installing the compressor;
Large oil reserve and more refrigerant charge than most other compressors, longer service life.
The corporate color of the compressor is blue.
Danfoss Maneurop is working to expand the power range from 3.5 to 25 hp. and introduces new refrigerants. In addition to developments in the use of ozone-friendly refrigerants R-407C and R-134A and in order to fight for a cleaner environment, Danfoss Maneurop began using R-410A refrigerant in compressors from 3.5 to 6.5 hp.
Remote and centralized cooling supply
The traditional scheme of refrigeration supply to commercial enterprises is carried out on the basis of separate units, i.e., a separate refrigeration unit operates for each consumer.
But equipping stores with refrigeration equipment with built-in compressors turns into additional costs for the installation of air conditioners to divert heat flows to sales areas from built-in units.
Heat gains into sales areas from refrigeration units built into the equipment lead to a decrease in turnover and an increase in unforeseen costs.
Uncomfortable conditions for the buyer (high temperature in the sales area and high noise level, unpleasant odors) lead to the fact that he is in a hurry to leave the store, which leads to a decrease in turnover;
Uncomfortable conditions for sellers and service personnel lead to a decrease in the quality of service, therefore, the image of the enterprise falls and the turnover decreases;
The service life of built-in units is 2-3 times lower than when using remote refrigeration systems and 4-6 times lower than when using central units, as a result of which production costs for maintenance and replacement of equipment increase;
The operation of compressor equipment in extreme conditions with extremely high temperature and condensation pressure causes frequent equipment failures, and this leads to losses from product spoilage;
Additional costs for air conditioning increase the overall energy consumption of a company by 20-30%.
Refrigeration systems serving several consumers are much more efficient - remote and centralized refrigeration supply.
External refrigeration supply is a refrigeration supply system based on autonomous compressor and condensing units located in the engine room, isolated from retail premises. Moreover, each unit can provide several consumers with cold.
Centralized refrigeration supply (central) is a type of remote refrigeration system. It is a multi-compressor unit with a single microprocessor control, as a rule, based on semi-hermetic reciprocating or scroll compressors. For medium and low temperature consumers, two separate circuits are used.
Currently, such installations are most common in large grocery stores and supermarkets.
| Hypermarket (shopping center) | Supermarket | Minimarket | |
| Total cooling capacity, kW | |||
| including: for medium temperature consumers (-10 ° С) | |||
| for low-temperature consumers (-15 ° С) | |||
| Central | Central / condensing units | Condensing units |
|
| Average service life, years |
When using a centralized refrigeration system, not only operating costs, but often also capital costs, are significantly reduced. And the more cold consumers there are, the more profitable it is to use centralized refrigeration supply.
The installation of a central refrigeration supply allows using the heat of condensation for the needs of heating and heating of service water.
Depending on the refrigerating capacity and the requirements for its regulation, it has from 2 to 6 compressors connected in parallel and having common discharge and suction systems. Such a compression block, isolated from commercial and auxiliary premises, provides cold to 20-25 end users connected to it by refrigeration lines.
In addition, such systems are designed with the necessary power reserve, which allows for scheduled maintenance and emergency repairs of any refrigeration unit without loss of refrigeration supply to the equipment. Previously, such systems were produced mainly by manufacturers of prestigious and expensive brands. Currently, central cold is available to a wider range of consumers.
Distinguish between medium and low temperature installations of centralized systems with a total cooling capacity of up to 80 kW. These systems will allow to create a "seamless" line of display cases and reduce the noise level in the sales area to a minimum.
For the centralized refrigeration supply diagram, see Fig.
For cooling water or brine, as well as for direct cooling of air, in air conditioning practice, they use natural and artificial sources of cold.
Natural sources cold can be artesian water, water of mountain rivers and ice. To artificial sources include vapor compression, steam-water and air refrigeration machines. In air conditioning units, vapor compression machines are most often used.
Cooling and dehumidification of air often occurs at an initial water temperature of 8-10 °. Water at this temperature can be obtained from artesian sources. In mountainous areas, the river water temperature usually does not exceed 5 °. In the case of using artesian water or from a mountain river, it is necessary to continuously change such water as its temperature rises. Cold water in such installations directly from the network or with pumping is supplied to the air conditioner, where it is heated and then discharged into the drain or used for industrial needs.
The use of artesian water in some cases has known economic advantages over artificial sources of cold. If drains of great length are needed to drain heated water into a reservoir, the expediency of using artesian water should be established by means of technical and economic comparisons.
One of the disadvantages of artesian water as a source of cold is its rather high temperature, which in some cases does not allow to provide the necessary drying of the processed air.
Ice as a cold source can be used for small air conditioning units. At the same time, the quality of the ice must meet the sanitary and hygienic requirements.
Artificial sources of cold, in contrast to natural ones, have the advantage that they do not need to replenish the cooling medium in them.
The processes taking place in vapor compression refrigeration machines are associated with a change in the state of aggregation of the refrigerant circulating in the system.
If the pressure is reduced to 0.007 bar, then the water will begin to boil at a temperature of only 4 ° C - such are its properties. In this case, it would be enough to bring a coolant with a temperature of, for example, 10 ° C to the kettle, and with the help of this coolant, the water in the kettle would boil, like from a gas burner flame, and this coolant would be cooled, for example, to a temperature of 7 ° C, just as the products of gas combustion are cooled under a boiling kettle. A heat carrier cooled from 10 to 7 ° C is called a refrigerant, and it can be successfully used, for example, in air conditioning systems.
In the ABHM evaporator, just such processes take place. As a refrigerant in this machine, not freons are used, but as in a kettle - ordinary water, which boils in an evaporator, the pressure inside of which is close to absolute vacuum.
At the same time, the refrigeration machine should still be somewhat more complicated than a kettle. The evaporator vacuum will disappear as soon as steam begins to form from the water. To prevent this from happening, the steam must be removed. In conventional compressor chillers, steam generated by the boiling of refrigerants is sucked off by a compressor. Theoretically, it would be possible to suck off water vapor with a compressor, but in practice this problem is difficult to solve, because the specific volume of water vapor at low pressure is very large, and an excessively large compressor would be required. On this, the idea of a water refrigeration machine could go into the realm of fantasy, if such a substance as a solution of lithium bromide in water had not been discovered. A feature of this solution is its ability to greedily absorb (scientifically - "absorb") water vapor. If a concentrated solution of lithium bromide, called an absorbent, is sprayed in the same volume with the evaporator, then the vacuum in this volume will remain, since the vapor will go into solution. True, the absorbent will very soon lose its ability to absorb, the heat will be transferred to the circulating water circulating through the absorber coil and removed to the atmosphere through the cooling tower.
A weak solution from absorber A is fed by pump 3 to generator G, through the tubes of which a coolant circulates from a heat source T. Under the influence of this heat, steam from a weak solution will evaporate and rush through the louvers (shown by an arrow) into the space of condenser K cooled by circulating water, on the tubes of which the steam will condense, the condensate will return to the I evaporator, and the partially dehydrated (concentrated) lithium bromide solution will return to the absorber. The concentration of salt in the solution decreases, and at the same time its absorption capacity deteriorates. To maintain the absorption capacity of the solution at a constant high level, it is necessary to evaporate excess steam from it. And for evaporation, there is no more suitable energy than heat.
Invention: in refrigeration engineering. The essence of the invention: cold is obtained by compressing and expanding a fluorine-based refrigerant. Inorganic hexafluorides or their mixtures are used as a refrigerant.
The invention relates to refrigeration technology and can be used in gas-powered energy refrigerating machines and heat pumps containing a compressor and an expander, mainly of a turbine or centrifugal type. A method of obtaining cold in a refrigeration unit by compressing a gaseous refrigerant in a turbocompressor and expanding in a turboexpander is known from the prior art (see USSR ed. N 169543, class F 25 B 11/00, 1965; ed. USSR N 183773, class F 25 B 9/00, 1966; ed. of the USSR N 1433193, class F 25 B 9/00, 1990, ed. of the USSR N 1778468, class F 25 B 9/00, 1992 or patent Great Britain N 2174792, class F 4 H 1986). In this case, air, nitrogen, hydrogen, helium, xenon, freons or mixtures of gases are used as a gaseous refrigerant, as, for example, in the author of St. USSR N 565052, class. F 25 B 9/00, 1977; ed. USSR N 802348, cl. F 25 B 9 / 00.1981. The closest known to the invention is a method of obtaining cold in a refrigeration unit by compressing a gaseous refrigerant in a turbocharger and expansion in a turboexpander (see USSR ed. N 473740, class F 25 B 11/00, 1975), in which as The refrigerant is a mixture of gases based on fluorine compounds containing octafluorocyclobutane FS-318 (C 4 F 8) and difluorochloromethane F-22 (CHClF 2). However, this refrigerant has an environmentally detrimental effect on the ozone layer. The invention is aimed at expanding the selection of gaseous refrigerants for energy refrigerating machines or heat pumps with high heat capacity, providing an increase in cooling capacity and a decrease in the weight and size parameters of turbomachines used as a compressor and expander (expander) with predominantly cold production. The solution to this problem is provided by the fact that in the method of obtaining cold in a refrigeration unit by compressing a gaseous refrigerant based on fluorine compounds in a turbocompressor and expanding in a turboexpander, inorganic hexofluorides or a mixture thereof are used as a refrigerant. The use of heavy inorganic hexofluorides as a refrigerant when expanding the choice of the working medium to ensure various operating parameters of a refrigerating machine or a heat pump makes it possible to increase the refrigerating capacity due to their high heat capacity and density and to reduce the dimensions of the turbocompressor and turboexpander for the light of the possibility of operation at low rotor speeds. When implementing the method, regardless of the circuit design of a particular refrigeration unit or heat pump, an inorganic hexofluoride, for example XeF 6, circulates in a gaseous state along the working circuit; WF 6; MoF 6; UF 6, or a mixture of these gases. In this case, the specific type of hexofluoride compound is determined depending on the optimal combination of the required operating parameters with the thermophysical properties of the refrigerant by calculation.
Claim
A method of obtaining cold in a refrigeration unit by compressing a gaseous refrigerant based on fluorine compounds and expanding it, characterized in that inorganic hexafluorides XeF 6, WF 6, MoF 6, UF 6 or mixtures thereof are used as the refrigerant.
Similar patents:
The invention relates to the field of refrigeration engineering, in particular, to turbocompressor installations and can be used for cooling or freezing various products, both in stationary conditions and on vehicles, for example, on ships
The invention relates to a technique for compressing gases, and more specifically to compressors for compressing refrigerant vapors and gases, with high final temperatures of the end of compression, and designed to work as part of industrial compressor shops in all areas of using artificial cold and compressing air and other gases
The invention relates to refrigeration technology, and more specifically to methods of cooling (installations for their implementation and distribution manifolds of such installations), in which various products or articles located in a closed volume are cooled using a cryogenic liquid supplied to a given volume, heated, evaporated and forming various circulation circuits with a gas environment in this volume, washing the products or articles placed in the volume
-> 13.04.2011 - Methods of obtaining cold and characteristics of cooling sources
Getting cold is reduced to reducing the heat content in a solid, liquid or gas. Cooling is the process of taking away heat, leading to a decrease in temperature or a change in the state of aggregation of a physical body. Distinguish between natural and artificial cooling.
Free cooling Is the removal of heat from the cooled body into the environment. With this method, the temperature of the cooled body can be lowered only to the ambient temperature. This is the easiest way to cool without the need for energy.
Artificial cooling- This is the cooling of the body below the ambient temperature. For artificial cooling, a refrigeration machine or refrigeration units are used. This cooling method requires energy consumption.
There are several ways to obtain artificial cold. The easiest is cooling with ice or snow. Ice cooling has a significant drawback - the cooling temperature is limited by the ice melting temperature. Water ice, ice-salt mixtures, dry ice and liquid refrigerants (freons and ammonia) are used as coolers.
Ice-salt cooling is performed using crushed water ice and salt. Due to the addition of salt, the rate of ice melting increases and the temperature of ice melting decreases. Dry ice cooling is based on the action of solid carbon dioxide - when heat is absorbed, dry ice passes from a solid state to a gaseous state. With the help of dry ice, you can get a lower temperature than with water ice: the cooling effect of 1 kg of dry ice is almost 2 times more than 1 kg of water ice, no dampness occurs during cooling, the emitted carbon dioxide gas has preservative properties, contributes to better preservation of products. Dry ice is used for the transportation of frozen products, cooling of packaged ice cream, storage
The most common and convenient for use is machine cooling. Compared to other types of cooling, machine cooling has the following advantages:
- the ability to create a low temperature over a wide range;
- automation of the cooling process;
- availability of operation and maintenance, etc.
Machine cooling is most widely used in trade due to a number of advantages:
- automatic maintenance of a constant storage temperature depending on the type of food;
- rational use of a useful container for cooling products, ease of service;
- high efficiency and the ability to create the necessary sanitary and hygienic conditions for storing products.
Machine cooling is based on the property of some substances to boil at a low temperature, while absorbing a large amount of heat from the environment. Such substances are called refrigerants (refrigerants).
Refrigerants- these are working substances of steam refrigerating machines, with the help of which low temperatures are obtained. Refrigerants must have a high heat of vaporization, low boiling point, high thermal conductivity. At the same time, refrigerants must not be explosive, flammable or poisonous. The cost of refrigerants is important. Freon 12, Freon 22 and ammonia are the most suitable for these requirements. Freon is supplied to trade enterprises in metal cylinders, painted in aluminum color and labeled R12 or.
Steam Compression Chiller Operation Standard Cycle
Steam Compression Refrigeration Cycle is a thermodynamic process in which a liquid refrigerant is vaporized, compressed and condensed in a continuous cycle to cool a chamber or space.
Thermodynamic cycle are two or more interconnected processes that ultimately return the working fluid to its original state. The cycle of interconnected processes of a machine cooling system is called a steam compression refrigeration cycle. Simple cycle steam compression refrigeration machine.
A simple cycle of a steam compression refrigeration machine consists of four main processes: expansion, evaporation, contraction, and condensation. In these processes, the pressure, temperature and condition of the refrigerant change. In each individual process, the properties of the refrigerant change. But at the end of the last process, the refrigerant returns to its initial state with the same qualities that it had at the beginning of the first process, and a cycle is formed. The components for performing these processes are presented in the previous section.
To understand the cycle of a steam compression chiller, it is necessary to first consider each process separately. By understanding individual processes, you can analyze them in relation to other processes that make up the cycle. It is necessary to understand the interrelationship of the processes, as changes in one process cause corresponding changes in others that make up the cycle of a steam compression refrigeration machine.
The refrigerant in the receiver is in liquid and gaseous states at high temperature and pressure. During the cycle, the liquid refrigerant flows into the liquid line and then into the refrigerant flow regulator.
The refrigerant at the inlet of the flow regulator is in a liquid state at high temperature and pressure. As the refrigerant flows through the small opening of the valve or capillary tube, its pressure is reduced to that of the evaporator. A decrease in refrigerant pressure produces a corresponding decrease in the saturation temperature of the liquid refrigerant. As a result, some of the refrigerant boils and lowers the temperature of the rest of the liquid. The vapor-liquid mixture exits the refrigerant flow regulator and enters the evaporator.
Refrigerant at the evaporator inlet Is a cool vapor-liquid mixture with low temperature and pressure. The rest of the liquid evaporates at the saturation temperature, corresponding to the pressure in the evaporator. The evaporating liquid absorbs the latent heat in the chamber. The vapor leaving the evaporator is slightly overheated to prevent liquid from entering the compressor.
Refrigerant at the compressor inlet Is superheated steam at a lower temperature and pressure. The compressor causes the refrigerant to move due to the low pressure zone in the cylinders during suction. Since the pressure in the cylinder is lower than the vapor pressure in the evaporator, the refrigerant flows through the suction line to the compressor due to the pressure difference. In the suction line, steam absorbs heat from the environment, which further increases its superheat. When compressed, the temperature and pressure of the steam increase, and the heated steam under pressure is discharged into the discharge line.
Refrigerant at the condenser inlet is superheated steam at high temperature and pressure. Since the ambient temperature of the condenser is lower than the saturation temperature of the vapor, the refrigerant condenses. Thus, the latent heat of vaporization absorbed in the evaporator is transferred to the outside of the chamber. By the time the refrigerant reaches the bottom of the condenser, it gives off enough dry and latent heat, condenses and becomes slightly colder. The liquid leaves the condenser and enters the receiver in the same state in which it left it. The cycle ends. 1
