ITPD20130004A1 - REFRIGERATOR SYSTEM WITH EJECTOR - Google Patents

Description

DESCRIPTION

Field of application

The subject of the present invention is a refrigeration system with an ejector.

The refrigeration system according to the invention finds application in the refrigeration and air conditioning sector, and possibly also in the more specific sector of heat pumps.

In particular, the system is used both in refrigerated cabinets with built-in refrigeration unit (known in the sector as plug-in cabinets), and in large-scale systems, such as refrigeration units that serve several refrigerated cabinets in parallel.

State of the art

As is known, a conventional vapor compression refrigeration system (or heat pump) allows heat to be transferred from a cold source to a hot source through a refrigerant fluid operating according to a thermodynamic cycle which provides in sequence an evaporation stage. , a compression stage, a cooling stage and an expansion stage. For this purpose, the plant consists of a closed circuit comprising an evaporator, a compressor, a condenser or a gas cooler and an expansion organ, arranged in series. The refrigerant fluid absorbs heat from the cold source (environment to be cooled) in the evaporator, passing to the vapor state. The fluid is then brought to a higher pressure level in the compressor, to release heat to the hot source inside the condenser or gas cooler, to finally return to the evaporator flowing through the expansion element.

The circuit section between the compressor outlet and the expansion organ inlet is defined as the high pressure side of the circuit, while the circuit section between the outlet of the expansion and the compressor inlet is defined, on the other hand, as the low pressure side of the circuit.

As is known, a compression plant can operate according to a subcritical cycle or alternatively according to a transcritical cycle.

A subcritical cycle occurs when the pressure at which heat is transferred to the hot source is lower than the critical pressure of the refrigerant fluid. In this case, during the cooling stage the refrigerant fluid is in (biphasic) conditions of liquid-vapor equilibrium and the heat exchanger that realizes this stage functions as a condenser. In the high pressure branch of the system there is therefore a unique link between pressure and temperature.

A transcritical cycle occurs when the pressure is higher than the critical pressure of the refrigerant fluid. In this case, during the cooling stage the refrigerant fluid is in supercritical conditions (single phase) and can only undergo cooling without a phase change. The heat exchanger that realizes this cooling stage works as a gas cooler and not as a condenser. In the high pressure branch of the system, therefore, there cannot be a univocal link between pressure and temperature since these variables can take on values that are independent of each other.

The plant solution described above includes an additional exchanger as illustrated in Figures 1 and 2. More in detail, the refrigerant fluid is compressed (point 2a) by compressor C, cooled at constant pressure in the condenser / gascooler D (point 3a) and subcooled by an E (Suction Line Heat eXchanger, SLHX) exchanger to increase its cooling capacity (point 4a); the refrigerant flow is laminated in a lamination member B (point 5a) and sent to evaporator A (point 6a). Leaving the evaporator, the refrigerant is superheated (1) in order to subcool the refrigerant leaving the condenser / gascooler in the SLHX.

The advantages of this system solution are the following:

- simple configuration with reduced number of components,

- possibility of using inexpensive components: SLHX tube in tube and capillary as a rolling element,

- possibility of introducing a two-stage compressor as a primary compressor group.

As it does not provide for the presence of a liquid receiver, which acts as an accumulation and buffer, this system solution however has the disadvantage of not being equipped with a system for removing the formation vapor from lamination (hereinafter simply referred to as â € œflash gasâ €) , which would allow an improvement in cycle performance

In transcritical CO2 systems, the liquid receiver becomes a two-phase receiver and, both to avoid the danger of overpressure and to improve the energy performance of the cycle, it is common practice to remove the flash gas with a special removal system that controls its pressure inside the receiver.

Generally the flash gas is tapped, laminated and combined with the main flow leaving the evaporator. However, this solution is not energy efficient.

In accordance with a possible alternative plant solution, the flash gas is returned to the high pressure side, upstream of the condenser, by means of an auxiliary compressor, as envisaged for example in the Italian patent IT1351459 in the name of Costan S.p.A.

More in detail, as illustrated in Figures 3 and 4, this configuration with auxiliary compressor involves the division of the lamination process into two stages and the use of a compressor for the extraction of the flash gas vapor that is generated after the first lamination (lamination that brings the cooler to an intermediate pressure). The refrigerant (point 3b) passes through the condenser / gascooler D to be cooled; at the outlet (point 4b) it undergoes a first lamination in a back pressure valve B1 (point 5b), downstream of which there is a receiver F, in which the equilibrium condition between vapor and liquid is recorded. The two phases are separated. The liquid (point 6b) proceeds towards evaporator A (point 7b), after being further laminated in a second lamination valve B2, and subsequently towards the primary compressor C1 (point 1b), while the vapor is compressed in a auxiliary compressor C2 (point 8b). The outputs of the two compressors (points 2b and 9b) are mixed before entering the condenser / gascooler D (point 3b).

This system solution has some advantages: - possibility of replacing traditional systems in which the flash gas is removed with a lamination element and brought to conditions (1) and recompressed in the main compressor unit; therefore with an auxiliary compressor system, the main group compresses less flow than traditional systems with consequent energy savings,

- possibility of introducing a two-stage compressor as a primary compressor group.

However, this system solution also has some disadvantages:

- compared to the single compression stage configuration, it requires an additional compressor, a phase separator and two lamination valves instead of one, with an increase in costs and plant complexity;

- difficulty of application to cabinet systems with built-in refrigeration unit (hereinafter simply plug-in): in fact, volumetric flow rates can circulate in the auxiliary compressor which can be up to 10-20% of those circulating in the primary compressor unit; the reduced sizes of the plug-in systems would lead to the need to use auxiliary compressors of such small sizes that to date they are not available on the market.

There is therefore a need in the refrigeration sector to carry out a flash gas removal in a more efficient way from an operational point of view and less expensive and complex from a plant engineering point of view.

In general, systems equipped with an ejector have been proposed to improve the efficiency of the refrigeration systems.

The ejector is a machine without moving parts, which can be used both as a compressor and as a pump to raise the pressure of a fluid by feeding a fluid (of the same or different nature) under pressure conditions and different temperature. The ejector works on the basic principle, according to which a fluid with high momentum, meeting one with a low one, raises the pressure. The fluid with higher momentum (high pressure) is called primary flow or motor flow, while fluid with lower momentum (low pressure) is called secondary flow or entrained flow. The ejector has a structure with a first converging element, followed by a groove and then by a diverging element (diffuser). The internal energy possessed by the primary flow is transformed into kinetic energy. The effect is to lower the pressure to suck up the secondary flow. In the convergent section of the ejector, mixing is carried out and the speeds of the two flows are uniform. Downstream, in the throat section, a normal shock wave is generated which causes a violent transformation from kinetic energy to pressure energy. The outgoing flow obtained is generally a uniform biphasic mixture. The normal shock wave modifies the stagnation pressure by lowering it. This reduces the efficiency of the ejector. An alternative to the normal wave is the oblique wave which consists of a less violent transformation that generates a loss of stagnation pressure on the only normal component of the flow that passes through it.

A known system solution provides for the use of an ejector on the low pressure side (low side) to increase the pressure of the steam leaving the evaporator thus reducing the work of the compressor. The plant design of this configuration is described in Figures 5 and 6. The primary flow (motor flow) entering the ejector G is the refrigerant leaving the condenser D (gas cooler), while the secondary flow (entrained flow ) entering the ejector is the steam leaving evaporator A. In this configuration, due to the presence of a two-phase liquid-vapor flow at the ejector outlet, it is necessary to place a phase F that separates the saturated liquid, to be sent to the lamination valve B which feeds the evaporator A, from the saturated vapor, to be sent to the compressor C. A plant of this type is described for example in the English patent GB1132477.

Another system solution involves the use of an ejector on the high pressure side (high side) to increase the pressure of the steam leaving the compressor, thus reducing the work of the compressor itself. The plant layout of this configuration is described in Figures 7 and 8. The primary flow (motor flow) entering the ejector G is the refrigerant leaving a pump P fed by a fraction of refrigerant (in liquid phase in the case of subcritical work cycle, otherwise gaseous for a transcritical work cycle) at the outlet from condenser D (gas cooler in the case of transcritical work cycle), while the secondary flow (entrained flow) entering the ejector G is the steam leaving compressor C. In this configuration, in order for the primary flow to effectively carry the secondary flow, it is necessary to provide an active component such as pump P. A system of this type is described for example in the US application US20070101760 .

Plant solutions are also conceivable in which a simple single-stage refrigeration cycle with or without an SLHX (Suction Line Heat eXchanger) exchanger has been introduced as an ejector as a pressure recuperator, to reduce the compression ratios developed by the compressor to reduce cycle consumption. Currently none of the proposed solutions has found practical application in marketed products. Among the main causes is the fact that the ejector is a static device, that is, it has an excellent design design which corresponds to the pre-established conditions of the incoming flows (primary and secondary). Deviating from these optimum conditions leads to reductions in the efficiency of the ejector and therefore benefits on the refrigeration cycle. A typical example is the modification of the outlet temperature from the condenser / gascooler following changes in the conditions of the environment in which the refrigeration system works.

Presentation of the invention

Therefore, the purpose of the present invention is to eliminate or at least mitigate the drawbacks of the aforementioned prior art, providing a refrigeration system with an ejector that allows a more efficient removal of the flash gas and at the same time can also be applied to plug-in cabinets. using standard compressors available on the market.

A further object of the present invention is to provide a refrigeration system with an ejector which is constructively simple to produce and operationally simple to manage.

A further purpose of the present invention is to provide a refrigeration system with an ejector which, when the operating conditions of use of the system vary, allows efficient use of the ejector to increase the pressure of the refrigerant in order to reduce the ratios. of compression developed by the compressor and, with them, reduce cycle consumptions.

Brief description of the drawings

The technical characteristics of the invention, according to the aforementioned purposes, are clearly verifiable from the content of the claims reported below and the advantages thereof will be more evident in the detailed description that follows, made with reference to the attached drawings, which represent one or more forms of purely illustrative and non-limiting realization, in which:

- Figures 1 and 2 respectively show a simplified system diagram and the related thermodynamic cycle in a pressure-enthalpy P-h diagram of a traditional vapor compression refrigeration system, currently used in plug-in cabinets;

- Figures 3 and 4 respectively show a simplified system diagram and the related thermodynamic cycle in a pressure-enthalpy P-h diagram of a known vapor compression refrigeration system with removal of the flash gas by means of an auxiliary compressor;

Figures 5 and 6 respectively show a simplified system diagram and the related thermodynamic cycle in a pressure-enthalpy P-h diagram of a known vapor compression refrigeration system with ejector on the low pressure side;

- Figures 7 and 8 respectively show a simplified system diagram and the related thermodynamic cycle in a pressure-enthalpy P-h diagram of a known vapor compression refrigeration system with ejector on the high pressure side;

- Figures 9 and 10 respectively show a simplified system diagram and the related thermodynamic cycle in a pressure-enthalpy P-h diagram of a refrigeration system with ejector for removing the flash gas according to a first embodiment of the invention; - Figures 11 and 12 show respectively a simplified system diagram and the related thermodynamic cycle in a pressure-enthalpy P-h diagram of a refrigeration system with ejector for the removal of flash gas according to a second embodiment of the invention; - Figures 13 and 14 respectively show a simplified system diagram and the relative thermodynamic cycle in a pressure-enthalpy P-h diagram of a refrigeration system with ejector for the removal of flash gas according to a third embodiment of the invention; - Figures 15 and 16 respectively show a simplified system diagram and the related thermodynamic cycle in a pressure-enthalpy P-h diagram of a refrigeration system with ejector for the removal of flash gas according to a fourth embodiment of the invention; - Figures 17 and 18 show respectively a simplified system diagram and the relative thermodynamic cycle in a pressure-enthalpy diagram P-h of a refrigeration system with ejector for the removal of the flash gas according to a fifth embodiment of the invention; - Figures 19 and 20 respectively show a simplified system diagram and the related thermodynamic cycle in a pressure-enthalpy P-h diagram of a refrigeration system with an ejector as a pressure recovery unit according to the invention.

The elements or parts of elements in common between the embodiments described below will be indicated with the same numerical references.

Detailed description

With reference to figures 9 to 18, 100 indicates a refrigeration system with an ejector according to the invention as a whole, while with reference to figures 19 and 20, 200 indicates the refrigeration system as a whole. with ejector according to the invention. We now proceed to the detailed description of the refrigeration system 100 illustrated in Figures 9 and 18, to which independent claim 1 refers.

The refrigeration plant 100 operates with a refrigerant according to a vapor compression cycle. The cycle can be either subcritical or transcritical. In particular, CO2 can be used as a refrigerant.

According to a general embodiment of the invention, illustrated in the attached Figures 9, 11, 13, 15 and 17, the system 100 comprises a main circuit 100A and in this main circuit 100A it comprises:

- a condenser 110, which operates as a gas cooler if the cycle is transcritical;

- a first 111 and a second expansion member 113 arranged downstream of the condenser 110;

- a first liquid receiver 112 arranged between the two expansion members 111 and 113, in which the refrigerant separates into the liquid phase and into the vapor phase;

- an evaporator 114 arranged downstream of the second rolling member 113; And

- at least one primary compressor 115 arranged downstream of evaporator 114 and upstream of condenser 110.

Preferably, the first and second expansion members 111 and 113 each consist of a lamination valve.

The plant 1 comprises an ejector 116 in a secondary branch 100B of the main circuit 100A.

Ejector 116 is of the convergent-divergent type. The structure and operation of an ejector are known to a person skilled in the art and will therefore not be described in detail.

The ejector 116 comprises a first inlet 116a for a motor flow, a second inlet 116b for a entrained flow and an outlet 116c for ejection of the mixture of the two flows.

At the first inlet 116a, the ejector 116 is fluidly connected to the main circuit in the section downstream of the condenser 110 and upstream of the first expansion member 111 to take a fraction of the coolant flow as motor flow.

At the second inlet 116b the ejector is fluidically connected to the first receiver 112 to extract the vapor phase of the refrigerant (flash gas) from the receiver itself as a entrained flow.

At outlet 116c, ejector 116 is fluidically connected to the main circuit in the section between evaporator 114 and condenser 110 to discharge the ejected flow of refrigerant.

Compared to traditional systems in which the flash gas is laminated and combined with the refrigerant leaving the evaporator, in system 100 the mass flow processed by the primary compressor (or first stage) is reduced with consequent energy savings in the refrigeration cycle, thus carrying out a more efficient extraction of the flash gas.

Together with the greater efficiency in extracting the flash gas, as will be discussed in detail below, unlike the solutions of the known technique which provide for the extraction of the flash gas with an auxiliary compressor, the refrigeration system 100 according to the This invention is applicable not only to compressor racks, but also to single plug-in showcases using standard compressors available on the market.

In accordance with the two construction solutions illustrated in Figures 9 and 11, the plant 100 includes two distinct primary compressors: one of low pressure 115b, connected fluidically to the evaporator 114, and one of high pressure 115b, fluidically connected to the condenser 110 The outlet 116c of the ejector 116 is fluidically connected to the main circuit between these two primary compressors 115a, 115b.

Alternatively, the aforesaid at least one primary compressor can be a two-stage compressor 115, having a first low pressure stage 115b fluidically connected to the evaporator 114 and a second high pressure stage 115a fluidically connected to the condenser 110. The output 116c of the ejector 116 is fluidically connected to the main circuit at the compressor 115 between the two compression stages.

According to a first preferred embodiment solution, illustrated in Figures 9 and 10, the system 100 comprises a heat exchanger 117 which thermally connects the section of the secondary branch downstream of the outlet 116c of the ejector 116 with the section of main circuit which is comprised between the capacitor 110 and the first expansion member 111.

In particular, this heat exchanger 117 could be of the concentric tube type.

The operation of the system 100 is now described in detail with reference to Figures 9 and 10. The alphanumeric references from 1e to 14e identify the various sections of the system in the pressure-enthalpy P-h diagram of Figure 10.

At the outlet from the condenser 110 (point 5e), the refrigerant is divided; a fraction (secondary flow) is tapped (11e) and introduced into the ejector 116 as motor flow. The high energy possessed by the refrigerant in the conditions (11e) is used to extract the â € œflash gasâ € (12e). The divergent of the ejector will allow an output recompression (13e). As the refrigerant leaves the two-phase ejector, the introduction of exchanger 117 (IHX, Internal Heat Exchanger) allows to exploit its complete evaporation (13e) to subcool the primary flow refrigerant leaving condenser 110 (point 6e) up to the conditions (point 7e) of entry into the lamination valve; after exchanger 117 the secondary refrigerant flow completes evaporation before it is introduced into the compressor (point 3e). The primary flow is preferably laminated in a back pressure valve 111 (point 8e), enters the receiver, is tapped in the liquid phase (point 9e) and then laminated in the lamination valve 113 (point 10e). After complete evaporation in evaporator 114 (point 1e) the primary flow is compressed in the low pressure compressor 115b (point 2e), mixed with the flash gas (point 3e) and then compressed in the high pressure compressor 115a (point 4e) .

The system configuration according to the aforementioned first embodiment allows first of all to remove the flash gas in a less complex system-wise manner than in prior art solutions with auxiliary compressors. In general, in fact, an ejector is less complex than a compressor.

As already mentioned, compared to systems in which the flash gas is laminated and combined with the refrigerant leaving the evaporator, in the system 100 described above, the mass flow rate processed at the first compression stage is reduced with consequent energy savings in the refrigeration cycle. .

The presence of the exchanger 117 allows the (primary) flow of refrigerant to be strongly subcooled, reducing the steam title coming out of the lamination valve 111. The flow rate of flash gas tapped by the ejector is reduced while, at the same level of enthalpy ™ evaporator and required cooling capacity, the refrigerant flow rate at the first compression stage is constant. Consequently, the flow rate of refrigerant that is processed by the second compression stage (sum of that of the first stage and that of the flash gas) decreases with a consequent improvement in the performance of the cycle.

The system configuration includes components with reduced economic impact. The ejector and the exchanger 117 (IHX) are in fact low cost devices. This makes the first embodiment of the 100 system particularly suitable also for plug-in cabinets where a low economic impact is essential.

According to a second preferred embodiment, illustrated in Figures 11 and 12, the system 100 comprises a second liquid receiver 119, fluidically inserted in the secondary branch section downstream of the outlet 116c of the ejector 116. In such second receiver 119 the ejected refrigerant flow separates into the liquid phase and the vapor phase.

More in detail, this second receiver 119 is fluidically connected to the main circuit by means of a third expansion member 120 in the section between the second expansion member 113 and the evaporator 114 to recirculate the liquid phase in the main circuit 100A. The vapor phase is sucked by the second high pressure stage 115a of the two-stage compressor 115 or by the high pressure compressor 115a.

The operation of the system 100 is now described in detail with reference to Figures 11 and 12. The alphanumeric references from 1f to 16f identify the various sections of the system in the pressure-enthalpy P-h diagram of Figure 12.

The refrigerant leaving the ejector 116 (point 12f) is in two-phase conditions. The second liquid receiver 119 makes it possible to exploit the cooling power contained in the liquid fraction. In the receiver 119 the phases are separated. The liquid (point 13f) is tapped and laminated (point 14f) in the third rolling member 120 and then joined to the main flow (point 9f) to reach the evaporator after mixing (conditions point 15f). Otherwise, the vapor (point 16e) is combined with the gas leaving the first compression stage or the low pressure compressor 115b (point 2f) and the mixed fluid (point 3f) is compressed in the second compression stage or by the high pressure compressor. pressure (point 4f). The primary flow is laminated in a back pressure valve 111 (point 7f) and enters the first receiver 112. From there it is tapped in the liquid phase (point 8f) and then laminated into the lamination valve 113 (point 9f). After mixing with the secondary flow in the liquid phase, complete evaporation takes place in evaporator 114 (point 1f). The refrigerant is then compressed at the first compression stage or by the low pressure compressor 115b (point 2f).

The system configuration according to the aforementioned second embodiment also allows the flash gas to be removed in a less complex way than in prior art solutions with auxiliary compressors. Compared to the first configuration, the addition of a receiver is foreseen, the complexity of which is in any case less than that of a compressor. Even if compared to the first embodiment, the system configuration is complicated with the insertion of new elements (i.e. second receiver and third rolling element), the low economic impact of the same, however, makes the configuration of interest also for small applications such as plug-in desks.

Also the configuration of the plant according to the aforementioned second embodiment allows to reduce the mass flow rate processed in the first compression stage with consequent energy saving of the refrigeration cycle, although in a less significant way than in the first embodiment.

Furthermore, the separation of the liquid-vapor phases in the second receiver 119 - after the ejector - allows to recover the cooling capacity and consequently to improve the performance of the refrigeration cycle.

According to three alternative embodiments (third, fourth and fifth embodiment) illustrated in Figures 13 to 18, which will be better described later, the secondary branch 100B in which the ejector 116 is inserted can be connected to the circuit main compressor 100A downstream of the aforementioned at least one primary compressor 115 and upstream of the condenser 110.

Advantageously, the aforesaid at least one primary compressor 115 can be a single-stage compressor or a two-stage compressor (with a first low pressure stage and a second high pressure stage). Alternatively, the system 100 can include two primary compressors connected in series, one of which is low pressure and one is high pressure. In all three solutions, the secondary branch 100B in which the ejector 116 is inserted is connected to the main circuit 100A downstream of the primary compressor or compressor 115. In other words, the secondary branch is connected in the high part main circuit pressure 100A, i.e. in the part that is at the inlet pressure to the condenser 110.

In accordance with a third and fourth embodiment solution, illustrated respectively in Figures 13-14 and in Figures 15-16, the system 100 comprises at least one auxiliary compressor 118 fluidically inserted in the secondary branch downstream of the output of the Ejector 116. Operationally, this auxiliary compressor 118 raises the pressure of the flow leaving the ejector to the same pressure level as the refrigerant entering the condenser 110.

More in detail, according to the third embodiment (Figures 13 and 14), the system 100 includes a heat exchanger 117 which thermally connects the section of the secondary branch downstream of the outlet 126c of the ejector 126 and upstream of the auxiliary compressor 118 with the section of the main circuit which is comprised between the condenser 110 and the first expansion member 111.

The operation of the system 100 is now described in detail with reference to Figures 13 and 14. The alphanumeric references from 1g to 14g identify the various sections of the system in the pressure-enthalpy P-h diagram of Figure 14.

From the flow leaving the condenser 110 (point 4g) a fraction is tapped (point 10g) and introduced into the ejector 116 as motor flow. The high energy possessed by the refrigerant in the conditions of point 10g is used to draw the flash gas (point 11g). The divergent of the ejector will allow a recompression at the outlet (point 12g). The refrigerant leaving the ejector 116 is two-phase. The heat exchanger 117 (IHX) makes it possible to exploit its complete evaporation (point 13g) to subcool the refrigerant of the main flow leaving the condenser 110 (point 5g) up to the conditions of point 6g. The steam leaving the exchanger 117 (point 13g) undergoes compression with the auxiliary compressor 118 up to the high pressure conditions of the circuit (point 14g), where it mixes with the main flow (point 2g) entering the condenser 110 under the conditions of the point 3g. The primary flow is laminated in a back pressure valve 111 (point 7g), enters the first receiver 112. Here the refrigerant is tapped in the liquid phase (point 8g) and laminated in the lamination valve 113 (point 9g). After complete evaporation in evaporator 114 (point 1g), the refrigerant is compressed in the primary compressor 115 (point 2g) and mixed with the flash gas (point 3g). Compared to traditional systems, in which the flash gas is laminated and combined with the refrigerant leaving the evaporator, also the configuration of the system in accordance with the aforementioned third embodiment allows to reduce the mass flow rate processed by the primary compressor with consequent energy saving of the refrigeration cycle.

The presence of the exchanger 117 allows the (primary) flow of refrigerant to be strongly subcooled, reducing the steam title coming out of the lamination valve 111. The flow rate of flash gas tapped by the ejector is reduced while, at the same level of enthalpy ™ evaporator and required cooling capacity, the refrigerant flow rate at the first compression stage is constant. Consequently, the flow rate of refrigerant that is processed by the second compression stage (sum of that of the first stage and that of the flash gas) decreases with a consequent improvement in the performance of the cycle.

Compared to the technical solution with removal of the flash gas with auxiliary compressor, but without an ejector, with the configuration according to the aforementioned third embodiment of the invention there are relationships between the volumetric flow rate of the secondary flow (flash gas) and the volumetric flow rate of the much higher primary.

This has a double advantage:

- there is no longer a primary compressor and an auxiliary compressor of an exaggeratedly different size from each other; on the contrary they are roughly equivalent;

- the system configuration is adaptable both for large sizes (refrigeration units) and for small sizes (plug-in counters); in fact, it is no longer unthinkable to find commercially structured compressors to operate in the conditions of the auxiliary compressor.

Advantageously, compared to the prior art solution with auxiliary compressor, the auxiliary compressor works less since part of the pressure jump is given by the ejector.

Compared to the prior art solution with auxiliary compressor, the system scheme of the aforementioned third embodiment is more complicated due to the presence of the ejector and the IHX exchanger. However, these two components have a relatively low economic impact. In any case, as already said, the possibility of using commercial compressors for the auxiliary compressor makes the system 100 according to this third embodiment also applicable to plug-in showcases.

More in detail, according to the fourth embodiment (Figures 15 and 16), the system 100 comprises a second liquid receiver 119 fluidically inserted in the secondary branch section downstream of the outlet 116c of the ejector 116 and upstream of the auxiliary compressor 118. In this second receiver 119 the flow of refrigerant leaving the ejector separates into the liquid phase and the vapor phase. The second receiver 119 is fluidically connected to the main circuit 100A by means of a third expansion member 120 in the section between the second expansion member 113 and the evaporator 114 to recirculate the liquid phase in the main circuit. The vapor phase is sucked by the auxiliary compressor 118.

The operation of the system 100 is now described in detail with reference to Figures 15 and 16. The alphanumeric references from 1h to 16h identify the various sections of the system in the pressure-enthalpy P-h diagram of Figure 16.

A fraction of refrigerant is tapped from the flow leaving the condenser 110 (point 4h) (point 9h) and then introduced into the ejector 116 as motor flow. The high energy possessed by the refrigerant in the conditions of point 9h is used to suck the flash gas (point 10h). The divergent of the ejector will allow an outgoing recompression (point 11h). The refrigerant leaving the ejector 116 (point 11h) is in two-phase conditions. The second liquid receiver 119 located downstream of the ejector 116 (point 11h) allows to separate the two phases liquid and vapor and therefore to exploit the cooling power contained in the liquid fraction. The liquid (point 12h) is tapped and laminated (point 13h) and then joined to the main flow (point 8h) to reach, after mixing, the evaporator under the conditions of point 14h. The vapor (point 15h) is compressed by the auxiliary compressor 118 and brought back to a high pressure condition (point 16h) and combined with the gas leaving the primary compressor (point 2h). The primary flow, on the other hand, is laminated in a back pressure valve 111 (point 6h) and enters the first receiver 112. From here it is tapped in the liquid phase (point 7h) and laminated in the lamination valve 113 (point 8h). After mixing with the secondary flow (point 14h), complete evaporation takes place in evaporator 114 (point 1h) and the introduction into the primary compressor 115. Compared to traditional systems, in which the flash gas is laminated and joined to the refrigerant leaving the evaporator, also the system configuration in accordance with the aforementioned fourth embodiment allows to reduce the mass flow rate processed by the primary compressor with consequent energy saving of the refrigeration cycle, although in a less significant way compared to the first embodiment of the € ™ invention.

Compared to the technical solution with removal of the flash gas with an auxiliary compressor, but without an ejector, with the configuration according to the aforementioned fourth embodiment of the invention - similarly to the third embodiment - there are relationships between the volumetric flow rate of the secondary flow (flash gas) and the volumetric flow rate of the primary flow much higher. This has a double advantage:

- there is no longer a primary compressor and an auxiliary compressor of exaggeratedly different size from each other; on the contrary they are roughly equivalent;

- the system configuration is adaptable both for large sizes (refrigeration units) and for small sizes (plug-in counters); in fact, it is no longer unthinkable to find commercially structured compressors to operate in the conditions of the auxiliary compressor.

Advantageously, compared to the prior art solution with auxiliary compressor, the auxiliary compressor works less since part of the pressure jump is given by the ejector.

The separation of the phases in the second receiver 119 (downstream of the ejector) allows the recovery of cooling power with consequent improvement in the performance of the refrigeration cycle.

More in detail, according to the fifth embodiment (Figures 17 and 18), the system 100 comprises at least one pump 121 fluidically inserted in the aforementioned secondary branch 100B upstream of the first inlet 116a of the ejector 116. The pump 121 raises the pressure of the motor flow of the ejector 116 so that the pressure of the ejected flow is equivalent to that of the refrigerant entering the condenser 110.

The operation of the system 100 is now described in detail with reference to Figures 17 and 18. The alphanumeric references from 1i to 12i identify the various sections of the system in the pressure-enthalpy P-h diagram of Figure 18.

In this configuration, the energy of the refrigerant is increased which, having come out of the condenser 110 (point 4i), is tapped from the main flow (point 9i), up to the conditions of point 10i, by means of a pump 121 (in particular hydraulic) to be fed to the ejector 116 as motor flow. The pump 121 operates in such a way that the motor flow has a pressure level so that it not only manages to tap the flash gas (point 11i), but also manages to bring the flow out of the ejector (point 12i) to have a pressure equal to that of the main flow leaving the compressor 115 (point 2i); the two flows are mixed and enter the condenser 110 (point 3i). The main flow (point 5i) is laminated in a back pressure valve 111 (point 6i) and collected in the first receiver 112. From here the refrigerant is tapped in the liquid phase (point 7i) and laminated in the main lamination member 113 (point 8i). Once evaporation in the evaporator is complete, the refrigerant enters the compressor (point 1i). As already mentioned, the vapor phase present in the first receiver 112 is sucked as a entrained fluid by the ejector 116. Compared to traditional systems, in which the flash gas is laminated and combined with the refrigerant leaving the evaporator, also the system configuration according to the aforesaid fifth embodiment it allows to reduce the mass flow rate processed by the primary compressor with consequent energy saving of the refrigeration cycle.

Compared to the configurations according to the invention (third and fourth embodiment) with auxiliary compressor, there is a reduction in consumption since, with the same pressure jump, a pump consumes less than a compressor.

In this fifth embodiment the auxiliary compressor is replaced with two components, the ejector and the pump, with consequent system complication. These two components are, however, relatively inexpensive. Even in this particular configuration, the system is therefore adaptable to both high system sizes (refrigeration units) and low system sizes (plug-in counters).

We now proceed to the detailed description of the refrigeration system 200 illustrated in Figures 19 and 20. The system 200, to which independent claim 12 refers. In particular, the system 200 - as the operating conditions of use vary refrigeration system (i.e. condenser temperature and evaporator temperature) - allows efficient use of the ejector as a pressure recovery unit, to reduce the compression ratios developed by the compressor and thus reduce cycle consumption.

The refrigeration system 200 operates with a refrigerant according to a vapor compression cycle. The cycle can be either subcritical or transcritical. In particular, CO2 can be used as a refrigerant.

According to a general embodiment of the invention, illustrated in the attached Figures 19 and 20, the system 200 comprises a main circuit 200A and in this main circuit 200A it comprises:

- a capacitor 210;

- an expansion member 211 arranged downstream of the condenser 210;

- an evaporator 214 arranged downstream of the second rolling member 113;

- compression means 215 which are arranged downstream of the evaporator 214 and comprise a first low pressure compression stage 215b, fluidically connected to the evaporator 214, and a second high pressure compression stage 215a, fluidically connected to the condenser 210.

Preferably, the expansion member 211 is each constituted by a lamination valve.

The plant 200 comprises an ejector 216 disposed between the two compression stages 215a, 215b.

Ejector 216 is of the convergent-divergent type. The structure and operation of an ejector are known to a person skilled in the art and will therefore not be described in detail.

The ejector 216 comprises a first inlet 216a for a motor flow, a second inlet 126b for a entrained flow and an outlet 216c for ejection of the mixture of the two flows.

As shown in Figure 19, the ejector 216 is fluidically connected to the first low pressure stage 215b at the second inlet 216b and to the second high pressure stage 215a at the outlet 216c.

The plant 200 also includes:

- a liquid receiver 212 interposed in the main circuit between the outlet 216c of the ejector 216 and the second high pressure stage 215a; in the receiver 212 the refrigerant ejected by the ejector separates into the liquid phase and the vapor phase; And

- a secondary branch 200B which connects the receiver 212 in parallel to the first inlet 216a of the ejector 216 and comprises at least one pump 221 which recirculates the liquid phase to the first inlet of the ejector 216; the vapor phase of the refrigerant is sucked by the second high pressure stage 215a of the compression means.

Operationally, the ejector 216 defines a third compression stage, intermediate between the two compression stages at low pressure 215b and high pressure 215a.

Thanks to the invention, the ejector 216 works between two pressures, that is that of the motor flow and that of the entrained flow, which are intermediate to the pressure of the evaporator 214 and that of the condenser 210. These two pressures correspond to the pressures impressed on the flows by the pump 221 and by the first low pressure compression stage 215b. These two pressures are therefore adjustable, acting respectively on the pump and on the first compression stage 215b.

In this way it is always possible to make the ejector work under fixed and non-variable working conditions. In particular, it is therefore possible to make the ejector (which is in itself a static device) work in the optimal design conditions which correspond to predetermined conditions of the motor (primary) and entrained (secondary) input flows. Thanks to the invention, for example, changes in the refrigerant outlet temperature from the condenser as a result of changes in the conditions of the environment in which the refrigerator works do not lead the ejector to deviate from optimum conditions, thus avoiding reductions the efficiency of the ejector and therefore the benefits on the refrigeration cycle. Preferably, the system 200 comprises a heat exchanger 217 which thermally connects the section of the secondary branch between the receiver 212 and the pump 221 with the section of the main circuit comprised between the evaporator 214 and the first low compression stage pressure 215b. This gives the safety of pumping liquid into the pump and not liquid and vapor.

Advantageously, the compression means 215 can consist of a single two-stage compressor 215, the two stages of which define said first low pressure stage (215b) and said second high pressure stage (215a).

Alternatively, the compression means can consist of two distinct primary compressors 215a, 215b, of which a first compressor 215b defines the aforementioned first low pressure stage and a second compressor 215a defines the aforementioned second high pressure stage.

The operation of the system 200 is now described in detail with reference to Figures 19 and 20. The alphanumeric references from 1l to 11l identify the various sections of the system in the pressure-enthalpy P-h diagram of Figure 20.

The two-phase flow out of the ejector (point 3l) is introduced into the liquid receiver 212 where the flow separates into the liquid and gas phases; the gas (point 4l) is compressed at the second stage of the compressor 215a (point 5l) and introduced to the condenser 210, from which it leaves (point 6l) to be laminated in the lamination valve 211 (point 7l). The liquid (point 9l), after having passed through the exchanger 217 (point 10l), passes through the pump 221 (point 11l) which increases its pressure and is used as a motive fluid in the ejector 216 for the gas leaving the first stage of compression 215b (point 2l). The main flow enters the evaporator 214 (point 7l), and then enters the heat exchanger 217 (point 8l) and, subsequently, into the first compression stage 215b (point 1l).

The plant 200 according to the invention makes the ejector operate at constant pressure conditions, unlike the solutions of the known technique mentioned in the introduction.

Compared to prior art solutions without an ejector, the compressor unit operates with lower pressure jumps, with consequent energy savings.

The 200 system can be applied both in plug-in cabinets (low system size), and in large systems (refrigeration units).

The 200 system according to the invention, dividing the pressure jump into 3 steps, is particularly suitable for those refrigeration systems that have a large pressure jump.

The invention allows to obtain numerous advantages which have been exposed in the course of the description.

The refrigeration system 100 with ejector according to the invention allows a more efficient removal of the flash gas and is at the same time applicable also to plug-in cabinets using standard compressors available on the market.

The refrigeration system 200 with ejector according to the invention, as the operating conditions of use of the system vary, allows efficient use of the ejector as a pressure recovery unit, to reduce the compression ratios developed by the compressor and thus reduce the consumption of the cycle.

Both refrigeration systems 100 and 200 are constructively simple to build and operationally simple to manage.

The invention thus conceived therefore achieves the intended purposes.

Obviously, in its practical embodiment, it may also assume forms and configurations other than the one illustrated above without thereby departing from the present scope of protection.

Furthermore, all the details can be replaced by technically equivalent elements and the dimensions, shapes and materials used can be any according to the needs.

Claims (14)

CLAIMS 1. Refrigerating system with ejector, operating with a refrigerant according to a vapor compression cycle and comprising in a main circuit (100A): - a capacitor (110); - a first (111) and a second expansion member (113) arranged downstream of the condenser (110); - a first liquid receiver (112) arranged between the two expansion members (111; 113) in which the refrigerant separates into the liquid phase and the vapor phase; - an evaporator (114) arranged downstream of the second rolling member (113); - at least one primary compressor (115) arranged downstream of the evaporator (114) and upstream of the condenser (110); characterized in that it comprises in a secondary branch (100B) of said main circuit (100A) an ejector (116) which comprises a first inlet (116a) for a motor flow, a second inlet (116b) for a entrained flow and a ejection outlet (116c) of the mixture of the two streams, at the first inlet (116a) said ejector (116) being fluidly connected to the main circuit in the section downstream of the condenser (110) and upstream of the first expansion member (111) to withdraw a fraction of the refrigerant flow as engine flow and at the second inlet (116b) it is fluidically connected to the first receiver (112) to extract the vapor phase of the refrigerant from the receiver itself as entrained flow, at the outlet (116c) the ejector (116) being fluidically connected to the main circuit in the section between the evaporator and the condenser. to discharge the ejected flow of refrigerant. 2. Plant according to claim 1, wherein said at least one primary compressor is a two-stage compressor (115), having a first low pressure stage (115b) fluidically connected to the evaporator (114) and a second stage of high pressure (115a) fluidically connected to the condenser (110), the outlet (116c) of the ejector (116) being fluidically connected to the main circuit at the compressor (115) between the two compression stages. 3. Plant according to claim 1, comprising two distinct primary compressors, one of low pressure (115b) fluidically connected to the evaporator (114) and one of high pressure (115b) fluidically connected to the condenser (110), the outlet (116c) of the ejector (116) being fluidically connected to the main circuit between said two primary compressors (115a, 115b). 4. Plant according to claim 2 or 3, comprising a heat exchanger (117) which thermally connects the section of the secondary branch downstream of the outlet (116c) of the ejector (116) with the section of the main circuit which is ̈ between the capacitor (110) and the first expansion member (111). 5. Plant according to one or more of claims 2 to 4, comprising a second liquid receiver (119) fluidically inserted in the secondary branch section downstream of the outlet (116c) of the ejector (116), in said second receiver (119) the ejected refrigerant flow separating into the liquid and vapor phases, said second receiver (119) being fluidly connected to the main circuit through a third expansion member (120) in the section between the second expansion member (113 ) and the evaporator to recirculate the liquid phase in the main circuit, the vapor phase being sucked by the second high pressure stage (115a) of the two-stage compressor (115) or by the high pressure compressor (115a). 6. Plant according to claim 1, in which the secondary branch in which the ejector (116) is inserted is connected to the main circuit downstream of said at least one primary compressor (115) and upstream of the condenser (110). 7. Plant according to claim 6, comprising at least one auxiliary compressor (118) fluidically inserted in the secondary branch downstream of the outlet (116c) of the ejector (116), said auxiliary compressor (118) raising the pressure of the ejected flow at the same pressure level as the refrigerant entering the condenser (110). 8. Plant according to claim 7, comprising a heat exchanger (117) which thermally connects the section of the secondary branch downstream of the outlet (126c) (or à ̈ 116c) of the ejector (126) (or à ̈ 116) and upstream of the auxiliary compressor (118) with the section of the main circuit which is included between the condenser (110) and the first expansion member (111). 9. Plant according to one or more of claims 6 to 8, comprising a second liquid receiver (119) fluidically inserted in the secondary branch section downstream of the outlet (116c) of the ejector (116) and upstream of the compressor auxiliary (118), in said second receiver (119) the ejected refrigerant flow separating into the liquid phase and into the vapor phase, said second receiver (119) being fluidically connected to the main circuit through a third expansion member (120) in the section included between the second expansion member (113) and the evaporator to recirculate the liquid phase in the main circuit, the vapor phase being sucked by the auxiliary compressor (118). 10. System according to claim 6, comprising at least one pump (121) fluidically inserted in the secondary branch upstream of the first inlet (116a) of the ejector (116), said pump (121) increasing the pressure of the motor flow of the ejector so that the pressure of the ejected flow is equivalent to that of the refrigerant entering the condenser (110). 11. Refrigerating system with ejector, operating with a refrigerant according to a vapor compression cycle and comprising in a main circuit (200A): - a condenser (210); - an expansion member (211) arranged downstream of the condenser (210); - an evaporator (214) arranged downstream of the rolling member (213) (or 211?); - compression means (215) which are arranged downstream of the evaporator (214) and include a first low pressure compression stage (215b) fluidically connected to the evaporator (214) and a second high pressure compressor stage (215a) fluidically connected to the condenser (210); characterized by the fact of understanding: - an ejector (216) arranged between the two compression stages (215a, 215b), which comprises a first inlet (216a) for a motor flow, a second inlet (126b) (or 216b) for a entrained flow and an outlet (216c) for ejection of the mixture of the two streams, said ejector (216) being fluidically connected to the first low pressure stage (215b) at the second inlet (216b) and to the second high pressure stage (215a) at the ™ output (216c); - a liquid receiver (212) interposed in the main circuit between the outlet (216c) of the ejector (216) and the second high pressure stage (215a), in said receiver (212) the refrigerant ejected from the ejector separating into the liquid phase and the vapor phase; - a secondary branch (200B) which connects the receiver (212) in parallel to the first inlet (216a) of the ejector (216) and includes at least one pump (221) which recirculates the liquid phase, the vapor phase of the refrigerant being sucked by the second high pressure stage (215a) of the compression means. 12. Plant according to claim 11, in which the compression means are constituted by a single two-stage compressor (215), the two stages of which define said first low pressure stage (215b) and said second high pressure stage (215a ). 13. Plant according to claim 11, in which the compression means are constituted by two distinct primary compressors (215a, 215b), of which a first compressor (215b) defines said first low pressure stage and a second compressor (215a) defines said high pressure second stage. 14. System according to one or more of claims 11 to 13, comprising a heat exchanger (217) which thermally connects the secondary branch section between the receiver (212) and the pump (221) with the main circuit section between the evaporator (214) and the first low pressure compression stage (215b).