Vapor compression refrigeration apparatus and process

Abstract

A vapor compression refrigeration apparatus comprises a compressor (4) of the centripetal radial type. The compressor (4) comprises a case (7), a shaft (8) mounted in the case (7) and supported in the case (7) so that it can rotate around an its own main axis (X-X), a single rotor disk (9) solidly mounted on the shaft (8), coaxial to the main axis (X-X) and comprising at least one array of rotor vanes (17a, 17b, 17c) arranged on one front face of said rotor disk (9) and around the main axis (X-X). Leading edges of the stator vanes (17a, 17b, 17c) face opposite to the main axis (X-X) and extend parallel to said main axis (X-X).

Description

[0001] “Vapor compression refrigeration apparatus and process”

[0002] DESCRIPTION

[0003] Field of the finding

[0004] The present invention has as its object a vapor compression refrigeration apparatus (or refrigeration machine or heat pump) and a vapor compression refrigeration process, i.e. an apparatus and a process that transfer thermal energy through a vapor compression cycle (VCC). In particular, the present invention refers to a vapor compression refrigeration apparatus and process that use a centripetal radial compressor.

[0005] Definitions

[0006] In the present description and in the attached claims, the terms “axial,” “radial,” and “circumferential” all refer to the main axis and sole axis of rotation of the compressor. In the present description and in the attached claims, as “centripetal radial compressor” (in English “radial inflow compressor”) is intended a driving turbomachine wherein the flow of the working fluid with which it exchanges energy is directed mainly in a radial direction with respect to the axis of rotation of the rotor disk and from the periphery to the center of the compressor.

[0007] Background of the finding

[0008] Apparatuses based on thermodynamic vapor compression cycles (VCCs) are known to consume mechanical energy (or electricity) to transfer thermal energy from one environment to another. In these apparatuses, low boiling point refrigerants of organic type (commonly high or medium molecular weight), both synthetic and natural, instead of water, are preferably used for a more efficient energy conversion and better thermodynamic properties in the field of application. Thus, VCC systems have recently found increasing applications in various fields, such as district heating and district cooling of environments, industrial energy recovery, and heat generation.

[0009] Within such apparatuses, scroll-type compressors are known to be used. For example, public documents US12055142B2, US11971030B2, US11898558B2, US11982277B2, and US11953010B2 show scroll-type compressors used in vapor compression refrigeration cycles and plants. The public document US2023074153A1 shows a scroll-type compressor with multiple outlets.

[0010] Centripetal compressors of different type used in other areas are also known. For example, the document US5676801 describes a single-stage centripetal compressor for large volumetric flows applied to a desalination plant instead of a centrifugal compressor. The document US3052096 describes the combination of a centripetal compressor with a centrifugal turbine to create a radial turbo-gas for power generation. The document US3040971 shows different configurations of centripetal compressors. The configurations are characterized by multiple stages, co-rotating or counter-rotating rotors and adjustable guide vanes positioned at different points in the compression line. The document US2949224 shows a multistage supersonic centripetal compressor. The document US1644565A shows a single-stage centripetal compressor with a hollow shaft and helical rotor blade. In that industrial field, screw and centrifugal compressors are then known to be used. The document US2016 / 0273549A1 shows a centrifugal radial compressor used in a cooling system. The document ITMI20110684A1 shows an Organic Rankine Cycle (ORC) plant with a centrifugal radial turbine. The document ITUB20155317A1 shows a binary cycle geothermal plant ORC provided with a centrifugal radial turbine.

[0011] Summary

[0012] The Applicant has noted that vapor compression refrigeration apparatuses and processes of the known type are improvable in several respects, particularly in relation to their efficiency.

[0013] The Applicant has in fact noted that the efficiency of vapor compression refrigeration apparatuses and processes is related to the efficiency of their components and related steps and in particular of the compressor and compression step.

[0014] The Applicant has also noted that the cost of vapor compression refrigeration apparatuses depends on the manufacturing and maintenance costs of the compressor.

[0015] In particular, the Applicant has noted that the scroll-type and screw-type compressors are structurally complex while centrifugal radial compressors require the adoption of blades with special geometries to generate the change in direction of the working fluid flow from axial to radial-centrifugal. These typologies of compressors are therefore expensive to make and also to maintain. Furthermore, given their complexity, they sometimes prove to be poorly reliable.

[0016] The Applicant has also noted that axial compressors are subject to relatively large losses due to secondary flow generation and thus to low efficiencies that affect the overall efficiency of the apparatus and the vapor compression refrigeration process. The Applicant has therefore perceived the need to realize a vapor compression refrigeration apparatus and a vapor compression refrigeration process that will allow to overcome the drawbacks of the known apparatuses and processes.

[0017] The Applicant has therefore perceived the need to realize a vapor compression refrigeration apparatus and a vapor compression refrigeration process with high efficiency, reliable and with relatively low manufacturing and maintenance costs. The Applicant has also noted that, in particular if the working fluid used is a medium or high molecular weight refrigerant, the compression step within the VCC is characterized by very high inlet volumetric flow rates and large specific volume variations between inlet into the compressor and outlet from the compressor that poorly adapt to be handled by axial and radial centrifugal compressors.

[0018] The Applicant has therefore also perceived the need to realize a vapor compression refrigeration apparatus and a vapor compression refrigeration process that are optimized for the use of medium to high molecular weight refrigerants.

[0019] The Applicant has found that the above-mentioned objectives and others can be achieved by a vapor compression refrigeration apparatus and a vapor compression refrigeration process that adopt a particular centripetal radial compressor.

[0020] The Applicant has in particular found that the above-mentioned objectives and others can be achieved by a vapor compression refrigeration apparatus and a vapor compression refrigeration process according to the attached claims and / or the following aspects.

[0021] More specifically, according to a 1st independent aspect, the present invention refers to a vapor compression refrigeration apparatus, comprising: an evaporator operationally coupled to a low-temperature source; a compressor coupled with a motor; a condenser operationally coupled to a high-temperature source; an optional expansion device; piping connecting the evaporator, the compressor, the condenser and the optional expansion device to each other to define a closed circuit; a working fluid circulating in the closed circuit; wherein in the evaporator the working fluid absorbs heat from the low-temperature source and evaporates by cooling the low-temperature source, in the compressor the vaporized working fluid increases pressure and temperature to a value higher than a temperature of the high-temperature source, in the condenser the working fluid gives up heat to the high-temperature source and condenses by heating the high-temperature source, in the optional expansion device the working fluid expands and cools and then returns to the evaporator; wherein the compressor is of the centripetal radial type and comprises: a case, a shaft mounted in the case and supported in the case so that it can rotate around an its own main axis; a single rotor disk solidly mounted on the shaft, coaxial to the main axis and comprising at least one array of rotor vanes arranged on one front face of said rotor disk and around the main axis, wherein the leading edges of the rotor vanes face opposite to the main axis and extend parallel to said main axis.

[0022] According to a 2nd independent aspect, the present invention refers to a vapor compression refrigeration process, comprising the following steps: a) transferring heat from a low-temperature source to a working fluid until it evaporates to cool the low-temperature source; b) increasing pressure and temperature of the vaporized working fluid to a temperature value higher than a temperature of a high-temperature source; c) transferring heat from the working fluid to the high-temperature source to heat the high-temperature source and up to condense the working fluid; d) optionally condensing and cooling the expanded working fluid; repeating steps a), b), c) and optionally step d); wherein step b) is implemented through a compressor of the centripetal radial type comprising: a case; a shaft mounted in the case and supported in the case so that it can rotate around an its own main axis; a single rotor disk solidly mounted on the shaft, coaxial to the main axis and comprising at least one array of rotor vanes arranged on a front face of said rotor disk and around the main axis, wherein leading edges of the rotor vanes face opposite to the main axis and extend parallel to said main axis; wherein the working fluid flows over the rotor vanes from an area radially outside said at least one array of rotor vanes and toward the main axis.

[0023] The vapor compression refrigeration process of the 2nd aspect can be implemented through the vapor compression refrigeration apparatus of the 1st aspect and the apparatus of the 1st aspect is configured to implement the process of the 2nd aspect. The Applicant has first of all verified that the particular compressor used in the apparatus and process of the invention allows to increase the overall efficiency of the apparatus and process.

[0024] The Applicant has in fact verified that the claimed compressor is little affected by secondary losses, much less than axial compressors, and therefore results in high efficiency, so that the entire vapor compression refrigeration process is efficient. In fact, in the claimed compressor the centrifugal forces act on the fluid elements in such a way that is different from axial-flow compressors. In axial-flow compressors, the centrifugal forces produce a radial motion perpendicular to the axial direction of the main flow, whereas in radial-flow compressors the centrifugal forces oppose the main flow moving toward the axis of rotation, so centripetal radial compressors such as the claimed one are less affected by secondary losses.

[0025] The Applicant has verified that the apparatus and process according to the invention result reliable and with relatively low manufacturing and maintenance costs. In fact, the claimed compressor does not require the realization of vanes with complex (twisted) geometries to adapt to the change of fluid flow direction from axial to radialcentrifugal. This is an advantage both in designing the blades and in manufacturing the blade profiles using machine tools.

[0026] The Applicant has also verified that the claimed compressor is particularly suitable for the compression of medium to high molecular weight refrigerants in VCC cycles, for example for district heating, district cooling, and various industrial heat recovery and generation applications, for the following reasons.

[0027] The compression in VCC cycles for such applications is characterized by large volumetric flow rates at the compressor intake and the radial-flow compressor object of the present invention is suitable for large volumetric flow rates because it inherently offers a large passage area at the inlet, where the diameter of the rotor disk is maximum, allowing to realize first-stage vanes with an optimal aspect ratio and such that the performance of the vanes and the efficiency of the compressor are optimized. Furthermore, the radial centripetal configuration of the claimed compressor is characterized by a progressive decrease of the passage section through the compression stages and this favors the compression of the working fluid. Finally, it is almost always possible to operate the compressor without any bottleneck at the inlet. Moreover, the compression in VCC cycles is characterized by a large specific volume variation between intake and discharge (which means a high volumetric flow rate ratio), and the claimed compressor is suitable for large volumetric flow rate ratios because it optimizes the height of the vanes due to the fact that the diameter of the arrays of vanes decreases in the direction of flow.

[0028] Furthermore, the geometric and structural characteristics of the claimed compressor allow to realize a plurality of compression stages on the single rotor disk, and this allows to obtain high compression ratios, higher than 1.5, with low losses and leakages and relatively low manufacturing costs.

[0029] Further aspects of the process and / or of the apparatus according to the invention are described below.

[0030] In a 2nd aspect according to one of the preceding aspects, the leading edges of the rotor vanes are straight.

[0031] In a 3rd aspect according to the preceding aspect, each of the rotor vanes has a constant section along its own height.

[0032] The section of the compressor vanes is preferably constant and prismatic, since the peripheral velocity is constant throughout the entire passage section, and therefore the manufacturing of the vanes is relatively simple and fast. Moreover, the degree of reaction is constant along the vane and this contains secondary losses, favoring the efficiency.

[0033] In a 4th aspect according to one of the preceding aspects, the case of the compressor has an inlet chamber located radially outside the rotor disk and surrounding the rotor disk, the inlet chamber being in fluid communication with at least one compressor inlet connected to the evaporator.

[0034] In a 5th aspect according to the preceding aspect, the inlet chamber having a volute shape with a variable cross section, optionally the cross section is circular.

[0035] In a 6th aspect according to one of the preceding aspects, the case of the compressor has a main outlet located in a radially inward position with respect to said at least one array of rotor vanes, close to the main axis and connected to the condenser.

[0036] In a 7th aspect according to the preceding aspect, the main outlet is coaxial to the main axis. In an 8th aspect according to aspect 6 or 7, an exhaust diffuser is associated with the main outlet to divert the working fluid from radial to axial; preferably the diffuser is with diverging conduit.

[0037] In a 9th aspect according to the preceding aspect, the exhaust diffuser is fixed with respect to the case. The divergent conduit diffuser allows the recovery of kinetic energy at the outlet and thus a greater overall machine efficiency.

[0038] In a 10th aspect according to the preceding aspect, the exhaust diffuser comprises a body provided with a substantially conical outer lateral surface, arranged coaxial to the main axis and tapering toward the main outlet and an annular body having a substantially conical radially inner surface surrounding the substantially conical outer lateral surface; the substantially conical outer lateral surface and the substantially conical radially inner surface delimiting between them a conduit that diverges toward the main outlet.

[0039] In an 11th aspect according to the preceding aspect, a terminal end of the substantially conical body is rounded.

[0040] In a 12th aspect according to the preceding aspect, the substantially conical lateral surface has a concave portion connected to the rounded terminal end.

[0041] In a 13th aspect according to the preceding aspect, the substantially conical lateral surface has a radially peripheral flat portion substantially orthogonal to the main axis and connected to the concave portion.

[0042] In a 14th aspect according to one of the preceding aspects, it is provided at least one array of stator vanes integral with the case, arranged opposite the rotor disk and around the main axis.

[0043] In a 15th aspect according to the preceding aspect, said at least one array of stator vanes forms with said at least one array of rotor vanes a respective compression stage.

[0044] In a 16th aspect in accordance with aspect 14 or 15, said at least one array of stator vanes is located in a radially inward position with respect to the array of rotor vanes. In a 17th aspect according to aspect 14 or 15 or 16, leading edges of stator vanes face opposite to the main axis and extend parallel to said main axis.

[0045] In a 18th aspect according to one of the aspects 14 to 17, the leading edges of the stator vanes are straight.

[0046] In a 19th aspect according to one of the aspects 14 to 18, each of the stator vanes has a constant section along its own height. In a 20th aspect according to one of the aspects 14 to 19, each of the stator vanes extends cantilevered from the case and toward the rotor disk.

[0047] In a 21st aspect according to one of the aspects 14 to 20, the stator vanes are carried by a stator disk constrained to the case.

[0048] In a 22nd aspect according to one of the preceding aspects, each of the rotor vanes extends cantilevered from the rotor disk and toward the case.

[0049] In a 23rd aspect according to any of the aspects 1 to 22, the compressor comprises a plurality of compression stages, optionally from two to ten compression stages, preferably seven compression stages.

[0050] In a 24th aspect according to aspect 23, each compression stage comprises an array of rotor vanes and an array of stator vanes.

[0051] In a 25th aspect according to aspect 23 or 24, the stator vanes and rotor vanes of the compression stages have decreasing heights starting from a radially outermost compression stage toward a radially innermost compression stage.

[0052] In a 26th aspect according to one of the aspects 23 to 25, the case has at least one auxiliary inlet communicating with a respective inlet volume interposed between two successive compression stages.

[0053] In a 27th aspect according to one of the aspects 23 to 26, the case has at least one auxiliary outlet communicating with a respective outlet volume interposed between two successive compression stages.

[0054] In a 28th aspect according to one of the aspects 26 to 27, a radial distance between two successive compression stages located at said inlet volume or said outlet volume is greater, for example ten times greater, than radial distances between other compression stages.

[0055] The Applicant has verified that the greater distance allows to obtain the inlet volume or the outlet volume.

[0056] In a 29th aspect according to aspect 26 or 28, the piping comprises a branch connected to the auxiliary inlet or auxiliary outlet.

[0057] The Applicant has verified that the compressor object of the present invention can easily integrate one or more inlet or outlet ducts for the working fluid, avoiding the need to adopt additional compressors placed in series for VCC cycle configurations at multiple pressure levels, resulting in more system compactness, lower costs, higher reliability due to the reduction of the number of components. In a 30th aspect according to the preceding aspect, the branch connects a tract of piping located downstream of the condenser and upstream of the evaporator with the auxiliary inlet.

[0058] In a 31st aspect according to the preceding aspect, a condensate recovery tank is located downstream of the condenser and upstream of the evaporator.

[0059] In a 32nd aspect according to the preceding aspect, the branch connects a steam outlet of the condensate recovery tank with the auxiliary inlet and wherein a liquid outlet of the condensate recovery tank is connected to the evaporator.

[0060] In an aspect according to the preceding aspect, a heat recuperator is operationally coupled to the branch and the tract of piping directed to the evaporator.

[0061] In a 33rd aspect according to any one of the preceding aspects, the case comprises a front wall facing said at least one array of rotor vanes and a lateral wall facing a rear face of the rotor disk.

[0062] In a 34th aspect according to the preceding aspect, the front wall and the rear wall delimit between them and within the case a housing for the rotor disk.

[0063] In a 35th aspect according to aspect 33 or 34, a sleeve is connected to the rear wall and housing the shaft.

[0064] In a 36th aspect according to the preceding aspect, the shaft is supported in the sleeve by bearings.

[0065] In a 37th aspect according to one of the aspects 33 to 36 when the aspect 33 is in accordance with one of the aspects 26 to 32, the auxiliary inlet and / or auxiliary outlet is / are made through the front wall.

[0066] In a 38th aspect according to one of the aspects 33 to 37 and to one of the aspects 6 to 13, the main outlet is made through the front wall.

[0067] In a 39th aspect according to one of the preceding aspects, the rotor disk is brought to a terminal end of the shaft, so that said rotor disk is supported cantilevered in the case.

[0068] In a 40th aspect according to one of the preceding aspects and aspect 35 or 36, a support assembly is housed in the sleeve and the shaft is placed in the support assembly.

[0069] In a 41st aspect according to the preceding aspect when in accordance with aspect 36, the support assembly comprises a bush housing the bearings and a sealing device arranged near the rotor disk to prevent leakages of the working fluid to the sleeve. In a 42nd aspect, according to aspect 40 or 41 , the bearing assembly is removable from the sleeve during downtime to perform maintenance operations.

[0070] In a 43rd aspect, the shaft is axially constrained to the support assembly and connected in a removable way to the rotor disk (optionally via a removable Hirth joint), so that the support assembly together with the shaft can be axially removed from the sleeve while the rotor disk remains in place.

[0071] In a 44th aspect according to one of the preceding aspects, the compressor comprises inlet guide vanes (IGVs) arranged around said at least one array of rotor vanes and configured to radially divert the flow to said at least one array of rotor vanes.

[0072] In a 45th aspect according to the preceding aspect, an incidence angle of the inlet guide vanes is adjustable. This allows to extend the operating range of the compressor, adjust the vapor flow of the working fluid through the compressor and finally improve the efficiency of the VCC apparatus with partial load.

[0073] In a 46th aspect according to aspect 44 or 45, the compressor comprises a control unit and one or more actuators configured to modulate the variable incidence angle of the inlet guide vanes.

[0074] In a 47th aspect according to one of the preceding aspects, the compressor comprises an axial stage arranged downstream of said at least one array of rotor vanes, or upstream of said at least one array of rotor vanes.

[0075] In a 48th aspect in accordance with the preceding aspect, the axial stage comprises an array of rotor vanes and an array of stator vanes with leading edges arranged transversely according to the main axis.

[0076] In a 49th aspect according to one of the preceding aspects, the working fluid has a medium to high molecular weight.

[0077] In a 50th aspect according to the preceding aspect, the molecular weight of the working fluid is between 40 g / mol and 500 g / mol.

[0078] In a 51st aspect according to one of the preceding aspects, the working fluid is selected from the group comprising: hydrocarbons, ketones, siloxanes or fluorinated materials (including perfluorinated materials).

[0079] In a 52nd aspect according to the preceding aspect, the working fluid is preferably a hydrocarbon from the alkane family ortrans1-chloro-3,3,3-trifluoropropene.

[0080] In a 53rd aspect according to one of the aspects 1 to 48, the working fluid is of low molecular weight, such as water, carbon dioxide or ammonia. According to a 54th independent aspect, the present invention relates to a compressor of the centripetal radial type which comprises: a case; a shaft mounted in the case and supported in the case so that it can rotate around an its own main axis; a single rotor disk solidly mounted on the shaft, coaxial to the main axis and comprising at least two arrays of rotor vanes, each one arranged on a front face of said rotor disk and around the main axis, wherein leading edges of the rotor vanes face opposite to the main axis and extend parallel to said main axis; wherein two arrays of stator vanes integral with the case, each one arranged on a front face of said rotor disk and around the main axis, wherein leading edges of the stator vanes face opposite to the main axis and extend parallel to said main axis; each array of stator vanes together with a respective array of rotor vanes forming a compression stage; wherein the case has at least one main outlet located in a radially inward position with respect to the compression stages and next to the main axis; wherein the case has also at least one auxiliary inlet communicating with a respective inlet volume interposed between two successive compression stages and / or wherein the case has also at least one auxiliary outlet communicating with a respective outlet volume interposed between the two successive compression stages.

[0081] In a 55th aspect, the compressor of the 54th aspect comprises one or more of the characteristics shown in the preceding aspects while not necessarily being used in the context of a vapor compression refrigeration apparatus and / or process and can therefore be made the subject of a possible divisional application.

[0082] Further characteristics and advantages will appear more from the detailed description of preferred, but not exclusive, embodiments of a vapor compression refrigeration apparatus and process according to the present invention.

[0083] Description of figures

[0084] This description will be set forth below with reference to the attached drawings, provided for illustrative purposes only and, therefore, not limiting, in which:

[0085] ■ figure 1 schematically shows a vapor compression refrigeration apparatus according to the present invention;

[0086] ■ figure 2 shows a vapor compression refrigeration cycle implemented by the apparatus of figure 1 ;

[0087] ■ figure 3 shows a centripetal radial compressor used in the apparatus of figure 1 and in the cycle of figure 2; ■ figure 4 shows a vapor compression refrigeration apparatus according to an embodiment variant and according to the present invention;

[0088] ■ figure 5 shows a vapor compression refrigeration apparatus according to a further embodiment variant and according to the present invention; ■ figure 6 shows a variant of the compressor of figure 3 used in the apparatuses of figures 4 and 5.

[0089] Detailed description

[0090] With reference to the above figures, a vapor compression refrigeration apparatus has been overall indicated with reference number 1. The apparatus 1 comprises an expansion device 2, represented in the example by a laminating valve (but could also be an expansion turbine), an evaporator 3 operationally coupled to a low temperature source not shown, a compressor 4 mechanically coupled to a motor 5, a condenser 6 operationally coupled to a high temperature source not shown. Pipes connect the expansion device 2, the evaporator 3, the compressor 4, and the condenser 6 together to form a closed circuit in which a working fluid circulates. The working fluid is preferably a medium-high molecular weight refrigerant, for example with a molecular weight between 40 g / mol and 500 g / mol, and can be selected from the group comprising: hydrocarbons (for example, a hydrocarbon from the alkane family or trans1-chloro-3,3,3-trifluoropropene), ketones, siloxanes or fluorinated materials (including perfluorinated materials). In other embodiments anyway within the scope of the present invention, the working fluid may have a low molecular weight and may be water, carbon dioxide or ammonia.

[0091] The apparatus 1 is configured to implement a vapor compression refrigeration process according to the cycle shown in figure 2. In evaporator 3, the working fluid absorbs heat from the low-temperature source and evaporates by cooling the low-temperature source (step a: transferring heat from the low-temperature source to the working fluid until it evaporates to cool the low -temperature source); in compressor 4, the vaporized working fluid increases pressure and temperature to a value above a temperature of the high-temperature source (step b: increasing pressure and temperature of the vaporized working fluid to a temperature value higher than a temperature of a high-temperature source), in the condenser 6 the working fluid transfers heat to the high-temperature source and condenses by heating the high-temperature source (step c: transferring heat from the working fluid to the high-temperature source to heat the high-temperature source and up to condense the working fluid), in the expansion device 2 the working fluid expands and cools (step d: making the condensed working fluid expand and cool) and then returns to the evaporator 3 and starts the cycle again.

[0092] The compressor 4 of apparatus 1 that implements step b) is of the centripetal radial type and is shown in figure 3.

[0093] The compressor 4 comprises a case 7, a shaft 8 mounted in the case 7 and supported in the case 7 so that it can rotate around an its own main axis “X-X”, a single rotor disk 9 solidly mounted at a terminal end of the shaft 8 and coaxial to the main axis “X-X”, such that said rotor disk 9 is supported cantilevered in the case 7. The case 7 comprises a main portion that internally delimits a housing for the rotor disk. The main portion comprises a front wall 10 facing a front face of rotor disk 9 and a rear wall 11 facing a rear face of rotor disk 9. The front wall 10 and the rear wall 11 delimit between them and within the case 7 the housing for the rotor disk 9. The case 7 also comprises a sleeve 12 connected to the rear wall 11 and extending away from said rear wall 11. Within the sleeve 12 is housed a support assembly defined by a bush 13 within which are arranged bearings 14 and a sealing device 15 located near the rotor disk 9. The bush 13 is mounted integral to the sleeve 12 with the possibility of being removed from it to carry out maintenance operations. The sealing device 15 is mounted at an axial end of the bush 13 to sealably separate the housing from an inner volume of the sleeve 12 in which the support assembly is located, in such a way as to prevent leakages of the working fluid to the sleeve 12. The shaft 8 is located in the support assembly, supported by the bearings 14 and coaxial to the bush 13. The terminal end of shaft 8 carrying the rotor disk 9 protrudes into the housing while an opposite terminal end of the same shaft 8 is accessible from one end of the sleeve 12 to be connected to the motor 5, not shown in figure 3. The shaft 8 is hollow and, furthermore, the terminal end carrying the rotor disk 9 is provided with a Hirth-type semi-coupling coupled at the head to a respective Hirth semi-coupling machined on the rear face of the rotor disk 9. A tie rod 16 that passes through the cavity of shaft 8 keeps shaft 8 and rotor disk 9 solidly joined together. The shaft 8 is thus connected in a removable way to the rotor disk 9. Moreover, the shaft 8 is axially constrained to the support assembly, i.e. , it can freely rotate with respect to the bush 13 around its main axis “X-X,” thanks to the bearings 14, but it cannot move axially with respect to the bush 13. Therefore, by releasing the tie rod 16 from the shaft 8, it is possible to remove the support assembly together with the shaft 8 from the end of the sleeve 12 while the rotor disk 9 and the tie rod remain in the case 7. To this end, before releasing the tie rod 16, the rotor disk 9 is locked in the housing making it integral to the case 7 by means of appropriate devices, not shown. Eventually, such devices also allow to approach the rotor disk 9 to the rear wall 11 with the interposition of one or more sealing rings in such a way as to prevent the leakage of working fluid through the sleeve 12 during maintenance.

[0094] The compressor 4 comprises a first array of rotor vanes 17a that are arranged on the front face of the rotor disk 9 and around the main axis “X-X.” A second array of rotor vanes 17b is located in a radially inward position with respect to the first array and is radially spaced from the first array. A third array of rotor vanes 17c is located in a radially inward position with respect to the second array and is radially spaced from the second array.

[0095] Leading edges of the rotor vanes 17a, 17b, 17c face opposite to the main axis “X-X”, are straight and extend parallel to said main axis “X-X”. Each of the rotor vanes 17a, 17b, 17c extends cantilevered from the rotor disk 9 and toward the front wall 10 of the case 7. Furthermore, each of the rotor vanes 17a, 17b, 17c has a constant and prismatic section along its own height.

[0096] A stator disk 18 is installed in case 7, constrained to an inner face of front wall 10 and is integral to the case 7. A first array of stator vanes 19a is supported by the stator disk 18. The stator vanes 19a of the first array are arranged around the main axis “X-X” and are located in a radially inward position with respect to the first array of rotor vanes 17a. A second array of stator vanes 19b is located in a radially inward position with respect to the first array and is radially spaced from the first array. The stator vanes 19a of the first array are arranged around the main axis “X-X” and are located in a radially inward position with respect to the second array of rotor vanes 17b. A third array of stator vanes 19c is located in a radially inward position with respect to the second array and is radially spaced from the second array. The stator vanes 19a of the third array are arranged around the main axis “X-X” and are located in a radially inward position with respect to the third array of rotor vanes 17c.

[0097] Leading edges of the rotor vanes 19a, 19b, 19c face opposite to the main axis “X-X”, are straight and extend parallel to said main axis “X-X”. Each of the stator vanes 19a, 19b, 19c extends cantilevered from the stator disk 18 and toward the rotor disk 9. Furthermore, each of the stator vanes 19a, 19b, 19c has a constant and prismatic cross section along an its own height.

[0098] The first array of rotor vanes 17a together with the first array of stator vanes 19a form a first compression stage, the second array of rotor vanes 17b together with the second array of stator vanes 19b form a second compression stage, the third array of rotor vanes 17c together with the third array of stator vanes 19c form a third compression stage. As visible in figure 3, stator vanes 17a, 17b, 17c and rotor vanes 19a, 19b, 19c of the compression stages have decreasing heights from the first compression stage toward the third compression stage.

[0099] The case 7 has a main outlet 20 obtained through the front wall 10 and coaxial to the axis of rotation “X-X.” The main outlet 20 is located radially further inward from the third array of stator vanes 19c.

[0100] An exhaust diffuser 21 is fixedly installed in case 7 and is located between the third array of stator vanes 19c and the main outlet 20 to divert the working fluid from the third compression stage from radial to axial.

[0101] The exhaust diffuser 21 comprises a body provided with a substantially conical outer lateral surface 22, arranged coaxial to the main axis “X-X” and tapering toward the main outlet 20.

[0102] A terminal end of the substantially conical body faces the main outlet 20 and is rounded. The substantially conical lateral surface 22 has a concave portion connected to the rounded terminal end and a radially peripheral flat portion substantially orthogonal to the main axis “X-X” and connected to the concave portion.

[0103] The exhaust diffuser 21 further comprises an annular body having a radially inner surface 23 substantially conical surrounding the substantially conical outer lateral surface 22 and spaced from it. The substantially conical outer lateral surface 22 and the substantially conical inner radial surface 23 delimit between them a conduit that diverges toward the main outlet 20 and connects the third compression stage with said main outlet 20.

[0104] A volute 24 internally delimits an inlet chamber 25 located radially outside the rotor disk 9 and surrounding the rotor disk 9. The inlet chamber 25 surrounds the first compression stage, communicates directly with the first compression stage, and is also in fluid communication with an inlet 26 of compressor 4, shown schematically in figure 2. As visible in figure 3, the inlet chamber 25 has a circular and variable cross section along its circumferential development. The inlet 26 is connected to the evaporator 3, the main outlet 20 is connected to the condenser 6 (figure 1 ).

[0105] The working fluid enters through the inlet 26, fills the inlet chamber 25 and flows through the three compression stages, where it is compressed, along predominantly centripetal radial directions, and then is diverted by the discharge diffuser 21 (radial to axial) and exits through the main outlet 20 along an axial direction.

[0106] Figure 4 shows a variant of the refrigeration apparatus of figure 1 that, in addition to the elements above described, comprises a heat recuperator 27 (economizer). In particular, the piping downstream of condenser 6 is divided into a tract directed to evaporator 3, connected to the evaporator 3 and provided with the expansion device 2 (laminating valve), and a branch 28 connected to an auxiliary inlet 29 of compressor 4 (two-level pressure apparatus). The heat recuperator 27 thermally couples the branch 28 with said tract in such a way as to transfer heat between the working fluid in the branch 28 and the one in said tract. An auxiliary valve 30 is located on the branch 28 between the condenser 6 and the heat recuperator 27 while the expansion device 2 remains located between the heat recuperator 27 and the evaporator 3.

[0107] The further variant in figure 5 differs from the one in figure 1 because it also comprises a sub-cooler 31 located immediately downstream of condenser 6 and a condensate recovery tank 32 connected to sub-cooler 31. An auxiliary valve 30 is positioned between the sub-cooler 31 and the condensate recovery tank 32. A branch 28 connects a vapor outlet 33 of the condensate recovery tank 32, located on a top of tank 32, with the auxiliary inlet 29 of compressor 4 (two-level pressure apparatus), and a liquid outlet 34 of the condensate recovery tank 32, located at the base of tank 32, is connected to the evaporator 3. The expansion device 2 is located between the condensate recovery tank 32 and the evaporator 3.

[0108] The compressor 4 used in the vapor compression refrigeration apparatuses of figures 4 and 5 is shown in figure 6 and differs from the compressor of figure 3 in that the second compression stage (second array of rotor vanes 17b and second array of stator vanes 19b) is spaced from the third compression stage (third array of rotor vanes 17c and third array of stator vanes 19c) in such a way as to form a respective inlet volume 35 interposed between the two successive compression stages. A radial distance between the second and third compression stage is greater than the radial distance between the first and second compression stages, for example, ten times greater, in such a way as to form the mentioned inlet volume 35. The auxiliary inlet 29 (there are two in figure 6) is made through the front wall 10 and through the stator disk 18 and is in fluid communication with the inlet volume 35. Thus, the compressor 4 shown in figure 6 allows to realize the apparatuses 1 at two pressure levels of figures 4 and 5.

[0109] The centripetal radial compressor 4 of figure 6 and of the 49th aspect can also be used in apparatuses other than those of figures 4 and 5 and also in systems other than vapor compression refrigeration apparatuses and can thus be made the subject of a future divisional application.

[0110] As shown in both figure 1 and figure 6, the compressor 4 also comprises inlet guide vanes 11b (IGVs) mounted on case 7 through an IGV-bearing ring 11a, arranged around the first array of rotor vanes 17a, between the case 7 and the volute 24, and configured to radially divert the flow coming from the inlet chamber 25 to said first array of rotor vanes 17a. The inlet guide vanes 11b are mounted on the case 7 in such a way that their incidence angles can be adjusted. One or more actuators, not shown in the drawings, for example of pneumatic, hydraulic, electromechanical type, controlled by a control unit allow to modulate the incidence angle of the incoming guide vanes.

[0111] In embodiment variants also within the scope of the present invention but not shown in the drawings, the compressor 4 has an auxiliary outlet communicating with an emission volume instead of the auxiliary inlet 29 and the inlet volume 35 but the geometry is similar or identical to the one shown in figure 6.

[0112] In embodiment variants still within the scope of the present invention but not shown in the drawings, the compressor 4 also comprises an axial stage arranged downstream of the third array of stator vanes 19c, for example instead of the diffuser of figures 3 and 6, or arranged upstream of the first array of rotor vanes 17a. The axial stage comprises an array of rotor vanes and an array of stator vanes with leading edges arranged transversely with respect to the main axis “X-X”. The rotor blades of the axial stage can be mounted for example on the same rotor disk 9.

[0113] List of elements

[0114] 1 vapor compression refrigeration apparatus

[0115] 2 expansion device

[0116] 3 evaporator 4 compressor

[0117] 5 motor

[0118] 6 condenser

[0119] 7 case

[0120] 8 shaft

[0121] 9 rotor disk

[0122] 10 front wall

[0123] 11 rear wall

[0124] 11a IGV-bearing ring

[0125] 11b inlet guide vanes (IGV)

[0126] 12 sleeve

[0127] 13 bush

[0128] 14 bearings

[0129] 15 sealing device

[0130] 16 tie rod

[0131] 17a first array of rotor vanes

[0132] 17b second array of rotor vanes

[0133] 17c third array of rotor vanes

[0134] 18 stator disk

[0135] 19a first array of stator vanes

[0136] 19b second array of stator vanes

[0137] 19c third array of stator vanes

[0138] 20 main outlet

[0139] 21 discharge diffuser

[0140] 22 substantially conical outer lateral surface 23 substantially conical inner radial surface 24 volute

[0141] 25 inlet chamber

[0142] 26 inlet

[0143] 27 heat recuperator

[0144] 28 branch

[0145] 29 auxiliary inlet

[0146] 30 auxiliary valve

[0147] 31 sub-cooler 32 condensate recovery tank 33 vapor outlet

[0148] 34 liquid outlet

[0149] 35 inlet volume

[0150] X-X main axis

Claims

CLAIMS1. Vapor compression refrigeration apparatus, comprising:- an evaporator (3) operationally coupled to a low-temperature source; - a compressor (4) coupled with a motor (5);- a condenser (6) operationally coupled to a low-temperature source; - an optional expansion device (2);- piping connecting the evaporator (3), the compressor (4), the condenser (6) and the optional expansion device (2) to each other to define a closed circuit;- a working fluid circulating in the closed circuit;wherein in the evaporator (3) the working fluid absorbs heat from the low-temperature source and evaporates by cooling the low -temperature source, in the compressor (4) the vaporized working fluid increases pressure and temperature to a value higher than a temperature of the high-temperature source, in the condenser (6) the working fluid gives up heat to the high-temperature source and condenses by heating the high-temperature source, in the optional expansion device (2) the working fluid expands and cools and then returns to the evaporator (3); wherein the compressor (4) is of the centripetal radial type and comprises:- a case (7);- a shaft (8) mounted in the case (7) and supported in the case (7) so that it can rotate around an its own main axis (X-X);- a single rotor disk (9) solidly mounted on the shaft (8), coaxial to the main axis (X-X) and comprising at least one array of rotor vanes (17a, 17b, 17c) arranged on a front face of said rotor disk (9) and around the main axis (X-X), wherein leading edges of the rotor vanes (17a, 17b, 17c) face opposite to the main axis (X-X) and extend parallel to said main axis (X- X).

2. Apparatus according to claim 1 , wherein the leading edges of the rotor vanes (17a, 7b, 17c) are straight and each of the rotor vanes (17a, 7b, 17c) has a constant section along its own height.

3. Apparatus according to claim 1 or 2, wherein the case (7) of the compressor (4) has:an inlet chamber (25) located radially outside of the rotor disk (9) and surrounding the rotor disk (9), the inlet chamber (25) being in fluid communication with at least one inlet (26) of the compressor (4) connected to the evaporator (3), the inlet chamber (25) presenting a volute shape with a variable cross section; at least one main outlet (20) located in a radially inward position with respect to said at least one array of rotor vanes (17a, 17b, 17c), close to the main axis (X-X) and connected to the condenser (6); an exhaust diffuser (21) being associated with the main outlet (20) to divert the working fluid from radial to axial.

4. Apparatus according to claim 1 or 2 or 3, comprising at least one array of stator vanes (19a, 19b, 19c) integral with the case (7), arranged in front of the rotor disk (9) and around the main axis (X-X), said at least one array of stator vanes (19a, 19b, 19c) being located in a radially inward position with respect to the array of rotor vanes (17a, 17b, 17c) and forming with said at least one array of rotor vanes (17a, 17b, 17c) a respective compression stage; wherein leading edges of the stator vanes (19a, 19b, 19c) face opposite to the main axis (X-X) and extend parallel to said main axis (X-X), wherein the leading edges of the stator vanes (19a, 19b, 19c) are straight and each of the stator vanes (19a, 19b, 19c) has a constant crosssection along its own height.

5. Apparatus according to claim 4, wherein the compressor (4) comprises a plurality of compression stages; wherein the stator vanes (19a, 19b, 19c) and the rotor vanes (17a, 17b, 17c) of the compression stages have decreasing heights starting from a radially outermost compression stage toward a radially innermost compression stage.

6. Apparatus according to claim 5, wherein the case (7) has at least one auxiliary inlet (29) communicating with a respective inlet volume (35) interposed between two successive compression stages and / or at least one auxiliary outlet communicating with a respective outlet volume interposed between two successive compression stages; wherein the conduits comprise a branch (28) connected to the auxiliary inlet (29) or auxiliary outlet.

7. Apparatus according to claim 6, wherein a radial distance between two successive compression stages located at said inlet volume (35) or said outlet volume is greater than radial distances among other compression stages.

8. Apparatus according to claim 6 or 7, wherein the branch (28) connects a section of piping located downstream of the condenser (6) and upstream of the evaporator (3) with the auxiliary inlet (29); wherein a condensate recovery tank (32) is located downstream of the condenser (6) and upstream of the evaporator (3), wherein the branch (28) connects a steam outlet (33) of the condensate recovery tank (32) with the auxiliary inlet (29) and wherein a liquid outlet (34) of the condensate recovery tank (32) is connected to the evaporator (3), or wherein a heat recuperator (27) is operatively coupled to the branch (28) and to the section of piping directed to the evaporator (3).

9. Apparatus according to any of claims 6 to 8, wherein the case (7) comprises: a front wall (10) facing said at least one array of rotor vanes (17a, 17b, 17c) and a rear wall (11 ) facing a rear face of the rotor disk (9), wherein the front wall (10) and the rear wall (11) delimit between themselves and internally to the case (7) a housing for the rotor disk (9); a sleeve (12) connected to the rear wall (11) and housing the shaft (8), wherein the shaft (8) is supported in the sleeve (12) by bearings (14); wherein the auxiliary inlet (29) and / or the auxiliary outlet is / are obtained through the front wall (10).

10. Apparatus according to one of claims 1 to 9, wherein the rotor disk (9) is carried at one end of the shaft (8) such that said rotor disk (9) is supported cantilevered in the case (7).

11. Apparatus according to one of claims 1 to 10, wherein the working fluid has a medium to high molecular weight, optionally between 40 g / mol and 500 g / mol.

12. Vapor compression refrigeration process optionally implemented by apparatus (1) according to at least one of claims 1 to 11, said process comprising the following steps:a) transferring heat from a low-temperature source to a working fluid until it evaporates to cool the low-temperature source;b) increasing pressure and temperature of the vaporized working fluid to a temperature value higher than a temperature of a high-temperature source; c) transferring heat from the working fluid to the high-temperature source to heat the high-temperature source and up to condense the working fluid;d) optionally expanding and cooling the condensed working fluid;- repeating steps a), b), c) and optionally step d);wherein step b) is implemented through a compressor (4) of the centripetal radial type comprising:- a case (7);- a shaft (8) mounted in the case (7) and supported in the case (7) so that it can rotate around an its own main axis (X-X);- a single rotor disk (9) solidly mounted on the shaft (8), coaxial to the main axis (X-X) and comprising at least one array of rotor vanes (17a, 17b, 17c) arranged on a front face of said rotor disk (9) and around the main axis (X-X), wherein leading edges of the rotor vanes (17a, 17b, 17c) face opposite to the main axis (X-X) and extend parallel to said main axis (X- X);wherein the working fluid flows over the rotor vanes (17a, 17b, 17c) from an area radially outside said at least one array of rotor vanes (17a, 17b, 17c) and toward the main axis (X-X).

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