Distribution device for a liquid-vapor two-phase fluid and related method

Abstract

A distribution device (5) for a liquid-vapor two-phase fluid for a heat exchanger, comprising an inlet duct (6) and a section (7) provided with a plurality of outlet ducts (7a, 7b, 7n) for the liquid-vapor two-phase fluid. The inlet duct (6) comprises a first duct section (6A) and a second duct section (6B) arranged in sequence along the flow direction (F) of the liquid-vapor two-phase fluid through the distribution device (5). The first duct section (6A) has a uniform cross-section and is provided with a plurality of turbulator elements (8a, 8b, 8c, 8d) designed to cause pre-mixing of the liquid phase and vapor phase of the two-phase fluid. The second duct section (6B) has a progressively converging and diverging Venturi-shaped cross-section designed to cause remixing of the liquid phase and vapor phase of the two-phase fluid. The device of the invention offers the advantage of both dividing the two-phase fluid into equal flows in all the supply ducts to the heat exchanger and achieving complete mixing and uniform homogenisation of the liquid phase and the vapor phase in all the supply ducts of the two-phase fluid.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates, in general, to the technical field of refrigeration systems and concerns, in particular, a distribution device of the type used to mix a liquid-vapor two-phase fluid and distribute it into a plurality of outlet ducts towards the evaporator of a refrigeration machine. The invention also relates to a method for distributing a liquid-vapor two-phase fluid exiting towards the evaporator of a refrigeration machine by means of the aforementioned distribution device.

[0002] Conventional evaporators for refrigeration machines comprise a device for distributing a refrigerant fluid (e.g. R404A, CO 2 , propane, etc.), a heat exchanger and a manifold. During the operating cycle of the refrigeration machine, the refrigerant fluid, consisting of a liquid phase and a vapor phase and coming from a laminating valve, enters the distribution device and is divided into a plurality of flows that are directed into outlet ducts towards the heat exchanger of the evaporator. Here, the refrigerant fluid is completely transformed into vapor and then flows into a manifold that conveys it out towards a compressor (not shown).

[0003] In general, known distribution devices have the problem of providing inadequate mixing and uneven homogenisation of the two-phase refrigerant fluid exiting towards the evaporator heat exchanger of a refrigeration machine. For this reason, there is a particular need to improve the effectiveness of current distribution devices in order to solve the above-mentioned problems.

[0004] Some solutions in this direction, although partial and unsatisfactory, have already been proposed in the art. For example, patent publication EP4001799B1 discloses a distribution device for a liquid-vapor two-phase fluid for a heat exchanger having a hollow cylindrical body that defines a main duct and a plurality of secondary ducts that develop with a curvilinear trajectory partially twisting around the main duct and flow into it at different points along its longitudinal direction. The main duct has a fluid inlet area, preferably tapered inwards, and a distribution area from which diverging outlet ducts branch off to convey the fluid to a heat exchanger. The purpose of the secondary ducts is to promote the mixing and homogenisation of the liquid and vapor phases of the fluid, so that the vapor content of the fluid is the same in all the ducts exiting the distributor towards the heat exchanger. The main duct may have mixing elements on its surface, for example in the form of helical grooves or fins, whose purpose is to impart a swirling motion to the fluid, allowing further mixing of the liquid phase and the vapor phase.

[0005] The limitation of the above-described implementation is that the mixing of the liquid phase and the vapor phase of the two-phase fluid occurs only in the main duct of the distribution device, due to the effect of the secondary ducts and the mixing elements. However, this known solution does not guarantee complete mixing of the liquid phase and the vapor phase of the fluid before its distribution in the outlet ducts to the heat exchanger. Within the aforementioned ducts, the liquid stream may therefore adhere to the walls of the ducts. Furthermore, the mixing effect in the main duct of the distribution device is limited by the number of secondary ducts that can be created around the main duct, and this number cannot be increased arbitrarily because it is limited by the thickness of the body of the distribution device.SUMMARY OF THE INVENTION

[0006] The main purpose of the present invention is to provide a distribution device for a liquid-vapor two-phase fluid for a heat exchanger, as well as to provide a method for distributing a two-phase fluid using such a device, which not only allow the two-phase fluid to be divided into equal flows in all the supply ducts to the heat exchanger, but also to achieve complete mixing and uniform homogenisation of the liquid phase and the vapor phase in all the aforementioned supply ducts for the two-phase fluid.

[0007] This purpose of the invention is achieved with the distribution device for a liquid-vapor two-phase fluid for a heat exchanger according to claim 1. Preferred embodiments of the invention are set out in the remaining claims.

[0008] The device of the invention offers the advantage of both dividing the two-phase fluid into equal flows in all the supply ducts to the heat exchanger and achieving complete mixing and uniform homogenisation of the liquid phase and the vapor phase in all the two-phase fluid supply ducts.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Further features, objects and advantages will be more evident from the description of a preferred, but not exclusive, embodiment of the device of the invention illustrated, by way of non-limiting example, in the attached drawings, in which: Fig. 1 schematically shows the evaporator component of a refrigeration machine equipped with a refrigerant fluid distribution device, Fig. 2 is a sectional view of the distribution device according to the invention, and Fig. 3 shows schematic examples of turbulator elements in the distribution device according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Fig. 1 of the drawings schematically shows a typical evaporator of a refrigeration machine comprising a distribution device 1 for a refrigerant fluid (e.g., R404A, CO 2 , propane, etc.), a heat exchanger 2 and a manifold 3. During the operating cycle of the refrigeration machine, the refrigerant fluid coming from a laminating valve (not shown), and consisting of a liquid phase and a vapor phase, enters the distribution device 1 and is divided into a plurality of flows that are conveyed into outlet pipes 4 towards the heat exchanger 2 of the evaporator. Here, the refrigerant is completely transformed into vapor and then flows into a manifold 3, which conveys it out to a compressor (not shown).

[0011] For the correct operation of the evaporator of a refrigeration machine, it is important to ensure that the liquid-vapor two-phase refrigerant fluid flowing out towards the heat exchanger 2 is divided into flows with equal vapor content.

[0012] There are several reasons that can lead to the distribution of refrigerant fluid flows with uneven vapor content, the main ones being: fluid dynamic instability induced, for example, by the presence of a liquid stream adhering to the wall of the two-phase refrigerant fluid supply ducts or the presence of a heterogeneous two-phase refrigerant fluid flow upstream of the distribution device; different pressure drops in the various refrigerant fluid supply ducts; the presence of insoluble oils in the refrigerant fluid; manufacturing flaws.

[0013] As is well known, fluid dynamic instability is difficult to control, especially in refrigeration systems such as those considered here, wherein turbulence is used to thoroughly mix two-phase fluids undergoing a change of state.

[0014] The effects of different pressure drops can be mitigated through proper design of the heat exchanger. The effects caused by the presence of insoluble oil, on the other hand, are difficult to resolve, especially at low temperatures, and can cause two types of effects: the first is a sort of stagnation in particular areas of the refrigerant fluid circuit, for example inside siphons and capillaries, which causes increased localised pressure drops and, therefore, different refrigerant fluid flow rates; the second effect is to create unevenness in the two-phase refrigerant fluid mixture, before and after passing through the distribution device.

[0015] The effects of different pressure drops in the circuits due to inadequate design of the refrigeration machine evaporator clearly cannot be permanently eliminated by the distribution device, but the effects due to manufacturing flaws in the components and / or assembly anomalies can be significantly reduced by improving the manufacturing technique and assembly precision.

[0016] To overcome these drawbacks, the device of the invention has been developed, which is indicated as a whole with numeral 5 in Fig. 2 and is adapted to distribute a refrigerant fluid, comprising a liquid phase and a vapor phase, into a plurality of outlet ducts towards the heat exchanger of the evaporator of a refrigeration machine (not shown).

[0017] The distribution device 5 comprises an inlet duct 6 and a section 7 provided with a plurality of outlet ducts 7a, 7b, 7n for the two-phase refrigerant fluid. The inlet duct 6 is formed by a first duct section 6A and a second duct section 6B arranged sequentially along the flow direction F of the two-phase refrigerant fluid through the distribution device 5.

[0018] The first duct section 6A has a uniform cross-section and is provided with a plurality of turbulator elements 8 configured to cause premixing of the liquid phase and vapor phase of the two-phase refrigerant fluid entering the distribution device 5. Conveniently, the duct section 6A may have a chamfer or shoulder at the entry to allow connection to a supply pipe of the two-phase refrigerant fluid.

[0019] The second duct section 6B, on the other hand, has a Venturi-shaped cross-section, i.e. a progressively converging and diverging cross-section, designed to cause at its outlet a remixing of the liquid phase and vapor phase of the two-phase refrigerant fluid exiting towards the heat exchanger of the evaporator of the refrigeration machine.

[0020] Due to the aforementioned configuration of the inlet duct 6 of the distribution device 5, a double mixing of the liquid phase and vapor phase of the two-phase refrigerant fluid exiting towards the heat exchanger takes place. In the first section 6A of the inlet duct 6 of the distribution device 5, equipped with the aforementioned turbulator elements 8, a pre-mixing of the liquid phase and the vapor phase takes place, whereas in the second section 6B of the inlet duct 6, a remixing or final mixing of the liquid phase and the vapor phase of the two-phase refrigerant fluid takes place due to the Venturi effect.

[0021] In particular, at the throat or minimum cross-section of the Venturi-shaped second duct section 6B, the maximum velocity of the two-phase fluid flow through the Venturi is achieved and, simultaneously, the minimum pressure. Thanks to this dual effect, micro-evaporations are generated within the liquid phase of the refrigerant, which contribute to increasing turbulence and therefore mixing in the two-phase fluid flow.

[0022] This therefore results in more effective mixing and more uniform homogenisation of the liquid phase and vapor phase in all outlet ducts 7 of the distribution device. Furthermore, it prevents the liquid stream from adhering to the walls of the section 6B of the inlet duct 6 and to the walls of the outlet ducts 7a, 7b, 7n.

[0023] The method of distributing a two-phase refrigerant fluid with the distribution device 5 according to the invention therefore provides that the mixing and homogenisation of the liquid phase and vapor phase of the two-phase refrigerant fluid take place in two different areas of the inlet duct 6 of the distribution device 5, arranged in sequence with respect to the flow direction F of the two-phase refrigerant fluid through said distribution device, namely: a two-phase fluid pre-mixing area, located in a first section 6A of the inlet duct 6 of the distribution device 5 and having a uniform cross-section with a plurality of turbulator elements 8 designed to cause pre-mixing of the liquid phase and the vapor phase of said two-phase fluid; and a two-phase fluid remixing or final mixing area, located in a second section 6B of the inlet duct 6 of the distribution device 5, arranged downstream of the duct 6A and having a progressively converging and diverging Venturi-shaped cross-section, designed to cause remixing of the liquid phase and vapor phase of said two-phase fluid due to the Venturi effect.

[0024] Thanks to the pre-mixing of the two-phase fluid in the first section 6A of the inlet duct 6, it is possible to make the two-phase fluid flow substantially uniform even upstream of the second section 6B of the inlet duct 6 with the Venturi-shaped contracted cross-section and avoid phenomena of adhesion of the liquid stream to the walls of the inlet duct 6 and of the outlet ducts 7 of the distribution device 5.

[0025] Preferably, the distribution device 5 is made in a single piece by using an additive manufacturing or three-dimensional printing technique. As is well known, unlike conventional subtractive manufacturing techniques such as turning and milling, wherein an object is obtained from a block of material by mechanically removing chips, in additive manufacturing the object is produced from a three-dimensional computer model of the object itself, by means of the layered application and selective solidification of a particulate material. The main advantage of additive manufacturing applied to the present invention is that turbulator elements 8 with complex geometries and specific characteristics of interaction with the two-phase refrigerant fluid can be created. Furthermore, these turbulator elements 8 can be produced directly inside the distribution device 5 during its manufacturing phase. Figure 3 shows some examples of turbulator elements 8 that can be made in the section 6A of the inlet duct 6 by using the additive manufacturing technique, and specifically: turbulator elements 8a in the form of deflectors that protrude at an angle inside the aforementioned section 6A, turbulator elements 8b with a cusp arrangement and with the apex facing the refrigerant fluid inlet section, turbulator elements 8c in the form of a spiral on the inner wall of the duct 6A, and turbulator elements 8d with a spring shape.

[0026] From the above, it can be understood how the invention achieves its intended purpose, overcoming the aforementioned problems of known distribution devices.

[0027] Although the invention has been described and illustrated in relation to a preferred embodiment, it is clear that it is susceptible to numerous modifications and variations that are within the reach of a skilled man in the art and therefore fall within the scope of the appended claims. For example, the turbulator elements located in the first section of the inlet duct of the distribution device may have any suitable shape and be arranged in any suitable manner to induce turbulent motion in the two-phase fluid upstream of the second section of the inlet duct.

Claims

1. Distribution device (5) for a liquid-vapor two-phase fluid for a heat exchanger, comprising an inlet duct (6) and a section (7) provided with a plurality of outlet ducts (7a, 7b, 7n) for said liquid-vapor two-phase fluid, characterised in that said inlet duct (6) comprises a first duct section (6A) and a second duct section (6B) arranged in sequence along the flow direction (F) of said liquid-vapor two-phase fluid through said distribution device (5), wherein said first duct section (6A) has a uniform cross-section and is provided with a plurality of turbulator elements (8a, 8b, 8c, 8d) designed to cause pre-mixing of the liquid phase and the vapor phase of said two-phase fluid, and said second duct section (6B) has a progressively converging and diverging Venturi-shaped cross-section designed to cause remixing of the liquid phase and the vapor phase of said two-phase fluid.

2. Distribution device (5) according to claim 1, characterised in that said duct section (6A) has a chamfer or shoulder at the inlet to allow connection to a supply pipe of the two-phase refrigerant fluid.

3. Distribution device (5) according to claim 1, characterised in that said inlet duct (6) and said outlet ducts (7) are made in a single piece by means of an additive manufacturing technique.

4. Distribution device according to claim 1, characterised in that said turbulator elements (8a) are in the form of deflectors that protrude at an angle into the aforementioned section (6A) of the duct (6), the turbulator elements (8b) are arranged in a cusp shape with their apex facing the refrigerant fluid inlet section, the turbulator elements (8c) are spiral-shaped on the inner wall of the duct (6A), and the turbulator elements (8d) are spring-shaped.

5. Method for distributing a liquid-vapor two-phase fluid exiting towards the evaporator of a refrigeration machine by means of a distribution device (5) having an inlet duct (6) and a plurality of outlet ducts (7) for said liquid-vapor two-phase fluid, characterised in that it provides for pre-mixing of the liquid phase and the vapor phase of said liquid-vapor two-phase fluid in a first section (6A) of said inlet duct (6) of the distribution device (5) having a uniform cross-section and provided with turbulator elements (8), and a remixing or final mixing of the liquid phase and the vapor phase of said two-phase fluid in a second section (6B) of said inlet duct (6) having a Venturi-shaped cross-section, progressively converging and diverging.

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