EP2504655B1

EP2504655B1 - A heat exchanger with a suction line heat exchanger

Info

Publication number: EP2504655B1
Application number: EP10731708.3A
Authority: EP
Inventors: Claus Thybo; Lars Finn Sloth Larsen; Gunda Mader
Original assignee: Danfoss Micro Channel Heat Exchanger Jiaxing Co Ltd
Current assignee: Danfoss Micro Channel Heat Exchanger Jiaxing Co Ltd
Priority date: 2009-08-28
Filing date: 2010-06-30
Publication date: 2019-02-27
Anticipated expiration: 2030-06-30
Also published as: WO2011023192A2; WO2011023192A3; EP2504655A2

Description

FIELD OF THE INVENTION

The present invention relates to a heat exchanger, such as an evaporator or a condenser, for use in a vapour compression system, such as a refrigeration system or a heat pump, of the kind having at least two flow paths, e.g. in the form of at least two evaporators or at least two evaporator tubes, arranged fluidly in parallel between an inlet manifold and an outlet manifold. The heat exchanger of the invention is adapted to eliminate, or at least reduce, performance reducing effects of an occurring maldistribution of liquid and gaseous refrigerant among the two or more evaporator tubes, while maintaining a compact design of the heat exchanger and without the requirement of additional components. The present invention further relates to a vapour compression system comprising such a heat exchanger. In particular, the invention relates to an evaporator as defined in the preamble of claim 1, and as disclosed by figure 13 of US 2009/0019885A1 .

BACKGROUND OF THE INVENTION

Vapour compression systems, such as refrigeration systems, e.g. in the form of air condition systems or heat pumps, normally comprise a compressor, a condenser, an expansion device and an evaporator arranged in a refrigerant path. Gaseous refrigerant is compressed in the compressor, and the compressed refrigerant is fed to the condenser where it is condensed. The condensed refrigerant then enters the expansion device, e.g. in the form of an expansion valve, an orifice or a capillary tube, whereby refrigerant in a mixed gaseous/liquid phase is obtained, which is fed to the evaporator where it is evaporated before re-entering the compressor. It is desirable that the refrigerant leaving the evaporator is completely in the gaseous phase, since liquid refrigerant may cause damage to the compressor. On the other hand, mixed phase refrigerant should be present throughout the entire length of the evaporator. Thereby it is ensured that the entire length of the evaporator is used for evaporating refrigerant, and the potential capacity of the evaporator is utilised to the greatest possible extent.
In order to obtain this, the supply of refrigerant to the evaporator is often controlled on the basis of the so-called superheat. The superheat is the difference between the evaporating temperature and the temperature of the refrigerant leaving the evaporator. In the case that the superheat is positive and large, it is an indication that purely gaseous refrigerant is present in the last part of the evaporator, and that energy is used for heating the evaporated refrigerant. In the case that the superheat is zero, there is a risk that liquid refrigerant is passing through the evaporator. Thus, the supply of refrigerant to the evaporator should be controlled in such a manner that the superheat is kept at a positive, but small, level. Thereby it is ensured that mixed phase refrigerant is present throughout the entire length of the evaporator, or at least as close to the outlet as possible, while it is prevented that liquid refrigerant passes through the evaporator.
In the case that the evaporator comprises two or more evaporator tubes arranged fluidly in parallel, there is a risk that the liquid/gaseous refrigerant is distributed in an un-even manner among the evaporator tubes. Thereby the 'optimal filling degree', i.e. the amount of refrigerant supplied from the expansion device to the evaporator resulting in a filling as described above, varies from one evaporator tube to the next. As a consequence, with a given supply of refrigerant to the evaporator, some of the evaporator tubes may be passing liquid refrigerant, while other evaporator tubes may be passing gaseous refrigerant at a relatively high temperature, i.e. the potential refrigeration capacity of these evaporator tubes is not fully utilised. This is undesirable.
US 7,377,126 B2 discloses a refrigeration system having a pressurizer, a condenser, an expansion device and an evaporator. The evaporator has an inlet manifold, an outlet manifold, and a plurality of channels there between. The outlet manifold has a liquid outlet and a vapour outlet and provision is made for separation of refrigerant liquid from refrigerant vapour. The liquid refrigerant is passed through a superheating heat exchanger to obtain complete evaporation and superheating prior to passing to the pressurizer. In the refrigeration system disclosed in US 7,377,126 B2 the superheating heat exchanger is provided as an additional component. Thereby the size as well as the manufacturing costs of the refrigeration system is increased as compared to a refrigeration system without a superheating heat exchanger.

DESCRIPTION OF THE INVENTION

It is an object of embodiments of the invention to provide an evaporator having at least two evaporator tubes, the evaporator allowing for considerable reduction of performance reducing effects of an occurring maldistribution of liquid refrigerant among the evaporator tubes, while maintaining a compact design of a refrigeration system having the evaporator installed therein.
It is a further object of embodiments of the invention to provide an evaporator having at least two evaporator tubes, the evaporator allowing for considerable reduction of performance reducing effects of an occurring maldistribution of liquid refrigerant among the evaporator tubes, without requiring additional components.
It is an even further object of embodiments of the invention to provide a refrigeration system in which performance reducing effects of an occurring maldistribution of liquid refrigerant among two or more evaporator tubes is considerably reduced, while maintaining a compact design of the refrigeration system.
It is an even further object of embodiments of the invention to provide a refrigeration system in which performance reducing effects of an occurring maldistribution of liquid refrigerant among two or more evaporator tubes is considerably reduced, without requiring additional components.
The invention is defined in claim 1.
In the present context the term 'vapour compression system' should be interpreted to mean any system in which a flow of refrigerant circulates and is alternatingly compressed and expanded, thereby providing either refrigeration or heating of a volume. Thus, the vapour compression system may be a refrigeration system, an air condition system, a heat pump, etc.
The heat exchanger is of a kind comprising at least two flow tubes arranged fluidly in parallel. The heat exchanger further comprises an inlet manifold and an outlet manifold. The inlet manifold is arranged in fluid connection with inlet openings of each of the flow tubes, and the outlet manifold is arranged in fluid connection with outlet openings of each of the flow tubes. Thus, each flow tube defines a flow path between the inlet manifold and the outlet manifold, the flow paths being arranged fluidly in parallel. It should be noted that the two or more flow tubes may be in the form of two or more heat exchangers arranged fluidly in parallel between the inlet manifold and the outlet manifold, or in the form of two or more tubes forming part of a single heat exchanger.
Thus, refrigerant supplied to the heat exchanger is received in the inlet manifold and divided into two or more flow paths, each flow path leading refrigerant into one of the flow tubes. When the refrigerant has passed the heat exchanger, refrigerant from each of the flow tubes is once again collected in the outlet manifold to form a common flow of refrigerant.
The outlet manifold is provided with a suction line heat exchanger. The suction line heat exchanger is arranged in such a manner that direct thermal contact is provided between refrigerant delivered from the flow tubes and the suction line heat exchanger. Thereby heat transfer can take place between refrigerant leaving the flow tubes and entering the outlet manifold, and another fluid medium, the heat transfer taking place immediately as the refrigerant leaves the flow tubes. Preferably, heat exchange takes place between refrigerant flowing from an evaporator and refrigerant flowing from a condenser towards an expansion device arranged in fluid connection with the inlet manifold of the evaporator. Thereby the temperature of the refrigerant received in the outlet manifold of the evaporator is increased, and it is thereby possible to evaporate liquid refrigerant which has been allowed to pass through one or more of the evaporator tubes of the evaporator, at least to some extent. This allows the supply of refrigerant to the inlet manifold of the evaporator to be controlled in such a manner that liquid refrigerant is present throughout the entire length of all the evaporator tubes, or at least of most of the evaporator tubes, even if this has the consequence that liquid refrigerant is allowed to pass through one or more of the evaporator tubes. Such liquid refrigerant will be evaporated by means of the suction line heat exchanger, and thereby it is prevented that liquid refrigerant reaches the compressor. Thus, it is not necessary to operate some of the evaporator tubes with a non-optimal filling degree in order to prevent liquid refrigerant from reaching the compressor, and the overall potential refrigeration capacity of the evaporator is thereby utilised to a greater extent. Thereby a possible maldistribution of liquid refrigerant among the evaporator tubes can be compensated in the sense that the potential refrigeration capacity of the evaporator is utilised to the greatest possible extent without risking that liquid refrigerant reaches the compressor.
Providing the suction line heat exchanger in or as a part of the outlet manifold of a heat exchanger, such as an evaporator or a condenser, of a refrigeration system, allows for a compact design. Furthermore, the suction line heat exchanger is provided without the requirement for additional components of the vapour compression system. Finally, in the case that the heat exchanger is an evaporator, the heat transfer of the suction line heat exchanger is very good, since the cold refrigerant received in the outlet manifold comes directly into thermal contact with the second fluid medium as it leaves the evaporator tubes. In particular, arranging the suction line heat exchanger in such a manner that direct thermal contact is provided between refrigerant delivered from the flow tubes and the suction line heat exchanger, the refrigerant e.g. being sprayed directly onto the suction line heat exchanger, ensures a very efficient heat transfer.
In the present context the term 'direct thermal contact' should be interpreted to mean that the refrigerant delivered from the flow tubes meets the suction line heat exchanger immediately upon leaving the flow tubes, rather than, e.g., entering a first chamber before entering a second chamber housing the suction line heat exchanger. This has the advantage that possible droplets of liquid refrigerant leaving the flow tubes, in the case that the heat exchanger is an evaporator, are caught and evaporated before being mixed with the gaseous refrigerant leaving the flow tubes. Thereby a major part of the heat exchange taking place in the suction line heat exchanger is used for evaporating liquid refrigerant rather than for increasing the superheat of the gaseous refrigerant leaving the evaporator.
According to one embodiment the suction line heat exchanger may form an integral part of the outlet manifold. This may, e.g., be achieved by providing a specific design of the outlet manifold. For instance, the interior of the outlet manifold may be divided into two or more flow regions, at least one flow region being directly fluidly connected to the outlet openings of the flow tubes, and at least one flow region being arranged to allow a secondary flow of fluid medium to pass there through, and the regions being arranged relative to each other in such a manner that heat transfer can take place between fluid medium flowing in respective regions. The regions may advantageously be provided during manufacturing of the outlet manifold, e.g. using an extrusion technique.
As an alternative, the suction line heat exchanger may form a separate part inserted into the outlet manifold. According to this embodiment, the suction line heat exchanger and the outlet manifold are manufactured separately, and the suction line heat exchanger is subsequently inserted into the outlet manifold. According to this embodiment, the suction line heat exchanger may, e.g., be in the form of a separate tube section mounted in an interior part of the outlet manifold, the tube section being adapted to carry a flow of fluid medium which is adapted to exchange heat with the refrigerant leaving the flow tubes and entering the outlet manifold. In this case the tube section should be arranged inside the outlet manifold in such a manner that the refrigerant delivered from the flow tubes is brought directly into thermal contact with the tube section, e.g. being sprayed directly onto the tube section.
According to one embodiment, the suction line heat exchanger may be configured in such a manner that hot and/or cold fluid medium passes along the outlet manifold at least two times. Thereby the length of the flow path of the hot and/or cold fluid medium where hot and cold fluid medium is arranged in thermal contact is increased. Accordingly, the heat transfer area of the suction line heat exchanger is increased, thereby allowing a larger amount of liquid refrigerant to be evaporated in the suction line heat exchanger. Furthermore, this is achieved without increasing the dimensions of the outlet manifold, i.e. a very compact design is maintained. Finally, designing the suction line heat exchanger with multiple passages of fluid medium allows the hot/cold passages to be arranged relatively to each other in such a manner that a desired heat exchange takes place. For instance, hot passages may be arranged at a position where liquid refrigerant is expected to be passed from an evaporator into the outlet manifold, thereby efficiently ensuring that the liquid refrigerant is evaporated. It should be noted that this embodiment of the invention should be interpreted to cover a situation where the hot fluid medium passes along the outlet manifold two or more times, while the cold fluid medium passes along the outlet manifold only once, a situation where the cold fluid medium passes along the outlet manifold two or more times, while the hot fluid medium passes along the outlet manifold only once, and a situation where the hot fluid medium as well as the cold fluid medium passes along the outlet manifold two or more times.
The flow tubes may be in the form of microchannels. In evaporators comprising evaporator tubes of the microchannel kind there is a high risk of maldistribution of liquid refrigerant among the evaporator tubes. It is therefore highly desirable to be able to compensate such a maldistribution in a microchannel system.
The outlet manifold may be or comprise an outlet header. Similarly, the inlet manifold may be or comprise an inlet header. As an alternative, the outlet manifold may be of a kind which distributes refrigerant among two or more separate heat exchangers arranged fluidly in parallel.
The heat exchanger may be designed in such a manner that the inlet manifold and the outlet manifold are arranged adjacent to each other. This provides a compact design of the heat exchanger. Furthermore, since the heat exchanger is an evaporator, such a design allows the use of a so-called block valve for controlling the supply of refrigerant to the evaporator.
According to the invention,
the heat exchanger is be an evaporator. Hence, the suction line heat exchanger is arranged directly in the outlet manifold receiving refrigerant from one or more evaporator tubes arranged fluidly in parallel. Thereby the liquid refrigerant leaving the evaporator tubes and entering the outlet manifold comes into direct thermal contact with the secondary, hot, fluid medium before it reaches equilibrium with the hot suction gas. Thereby the performance of the suction line heat exchanger is improved as compared to a suction line heat exchanger arranged externally, since, in the latter case, the maldistributed fluid leaving the evaporator has undergone internal temperature equalisation before entering the suction line heat exchanger.
The outlet manifold and/or the suction line heat exchanger are shaped in a manner which separates liquid refrigerant delivered from the outlet openings of the flow tubes from gaseous refrigerant delivered from the outlet openings of the flow tubes. This is particularly useful since the heat exchanger is an evaporator. In this case the liquid refrigerant leaving the flow tubes is prevented from mixing with the gaseous refrigerant leaving the flow tubes, and the liquid refrigerant is led directly into thermal contact with the suction line heat exchanger, thereby ensuring that the liquid refrigerant is evaporated before it mixes with the gaseous refrigerant. Furthermore, the suction line heat exchanger may be designed in such a manner that a major part of the heat exchange between refrigerant leaving the flow tubes and fluid flowing in the suction line heat exchanger takes place with the liquid part of the refrigerant leaving the flow tubes. Thereby the energy available for heat exchange is used in the most efficient manner, i.e. for evaporating liquid refrigerant rather than for increasing the superheat of the gaseous part of the refrigerant.
The suction line heat exchanger may comprise one or more fins extending into an interior part of the outlet manifold. The fins may be arranged in such a manner that ridges and grooves are formed along a flow direction of fluid flowing in the suction line heat exchanger. The fins provide one way of providing the separation of liquid and gaseous refrigerant described above, since droplets of liquid refrigerant may be caught by the fins, and because the surface tension of the droplets retain them in the grooves. Furthermore, such fins improve the heat transfer of the suction line heat exchanger.
The suction line heat exchanger comprises a wall part defining an interface between a first flow region arranged to accommodate a heat exchanging fluid and a second flow region arranged to receive refrigerant delivered from the outlet openings of the flow tubes and entering the outlet manifold. According to this embodiment the suction line heat exchanger may advantageously be formed directly in the outlet manifold, e.g. by extruding the outlet manifold along with the wall part in a single process. As an alternative, a separate wall part may be mounted inside the outlet manifold, thereby dividing the interior of the outlet manifold into the first flow region and the second flow region. A design including such a wall part ensures in an efficient and easy manner that the refrigerant delivered from the flow tubes is brought directly into thermal contact with the suction line heat exchanger, in this case with the wall part.
The wall part may have a curved shape. A curved wall is stronger than a substantially plane wall having the same material thickness, in the sense that it is capable of withstanding larger forces acting on the wall, e.g. due to a pressure differences between opposing sides of the wall. Thus, by using a wall part having a curved shape, a desired strength of the wall part can be obtained with a smaller material thickness than would be required if a substantially plane wall part had been used. Accordingly, the costs and the weight of the suction line heat exchanger can be reduced without compromising the strength of the suction line heat exchanger. Furthermore, the heat transfer through the wall part is increased due to the reduced material thickness.
Alternatively or additionally, the wall part may be arranged asymmetrically with respect to the outlet openings of the flow tubes. According to this embodiment, the wall part is arranged relative close to some of the outlet openings, and further away from some of the other outlet openings. For instance, in the case that the heat exchanger is an evaporator, the wall part may be arranged closest to the outlet openings expected to pass liquid refrigerant, and further away from outlet openings expected to pass gaseous refrigerant. Thereby the liquid refrigerant is brought immediately into contact with the wall part, where it is evaporated, while the gaseous refrigerant is allowed to flow a short distance in the outlet manifold before being brought into thermal contact with the wall part. This is also a manner of separating the liquid and gaseous refrigerant leaving the evaporator tubes and of designing the heat exchange taking place in the suction line heat exchanger to primarily provide evaporation of liquid refrigerant rather than creating superheat in the gaseous part of the refrigerant.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in further detail with reference to the accompanying drawings in which

Fig. 1 is a schematic view of an evaporator, illustrating maldistribution of liquid refrigerant among five parallel evaporator tubes,
Fig. 2 is a schematic view of an evaporator, illustrating maldistribution of liquid refrigerant among three parallel evaporator sections,
Fig. 3 shows an outlet manifold of an evaporator,
Fig. 4 shows an outlet manifold of an evaporator,
Fig. 5 shows an outlet manifold of an evaporator,
Fig. 6 illustrates distribution of liquid and gaseous refrigerant leaving an evaporator,
Figs. 7-24 show outlet manifolds of evaporators, whereby figure 23 discloses an outlet manifold of an evaporator according to the invention,
Fig. 25 shows an evaporator comprising the outlet manifold of Fig. 3,
Fig. 26 illustrates the evaporator of Fig. 6 in a refrigeration system, and
Figs. 27-30 are diagrammatic views of refrigeration systems.

DETAILED DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic view of an evaporator 1 comprising five evaporator tubes 2 arranged fluidly in parallel, and each of the evaporator tubes 2 being fluidly connected to an inlet manifold 3. Thus, refrigerant received at the inlet manifold 3, via inlet opening 4, is distributed among the evaporator tubes 2. In the evaporator 1 shown in Fig. 1 the control of the supply of refrigerant to the evaporator 1 is based purely on a measured superheat value of the refrigerant leaving the evaporator 1, e.g. by adjusting an opening degree of an expansion valve in order to obtain a small, but positive, superheat.
The momentum of the liquid part of the mixed phase refrigerant supplied to the inlet manifold 3 tends to be higher than the momentum of the gaseous part of the mixed phase refrigerant. This has the consequence that more refrigerant in a liquid state is supplied to the evaporator tubes 2 arranged near the inlet opening 4, i.e. the centre tubes 2, than to evaporator tubes 2 arranged further away from the manifold inlet 4, i.e. the peripherally arranged tubes 2. Thereby the filling degree of the former evaporator tubes 2 is significantly higher than the filling degree of the latter evaporator tubes 2. This is illustrated by line 5, indicating the boundary between mixed phase refrigerant and purely gaseous refrigerant in each of the evaporator tubes 2. Ideally, this boundary 5 should be arranged immediately before the end of each evaporator tube 2, since in this case the entire length of each evaporator tube 2 is used for evaporating refrigerant, thereby utilising the potential refrigeration capacity of the evaporator 1 to the maximum extent, and no liquid refrigerant is allowed to pass through the evaporator 1.
However, it is clear from Fig. 1 that the uneven distribution of refrigerant among the evaporator tubes 2 renders it impossible to obtain the ideal situation described above. Since it may cause damage to the compressor to allow liquid refrigerant to pass through the evaporator 1, it is therefore necessary to operate the vapour compression system in such a manner that the potential refrigeration capacity of the evaporator 1 is not fully utilised.
Fig. 2 is a schematic view of an evaporator 1 comprising three evaporator sections 6, each comprising five evaporator tubes 2 arranged fluidly in parallel. For each evaporator section 6, each of the evaporator tubes 2 is fluidly connected to an inlet manifold 3. Thus, refrigerant received at an inlet manifold 3 via inlet opening 4 is distributed among the evaporator tubes 2 belonging to the evaporator section 6 in question. The evaporator sections 6 are also arranged fluidly in parallel, i.e. refrigerant received at the evaporator 1 is distributed among the inlet manifolds 3.
Within each evaporator section 6 it appears that the distribution of liquid refrigerant among the evaporator tubes 2 is substantially uniform, as indicated by lines 5. However, the distribution of liquid refrigerant among the evaporator sections 6 is highly uneven. Thus, in order to ensure that no liquid refrigerant is allowed to pass through the evaporator 1, it is necessary to control the supply of refrigerant to the evaporator 1 in such a manner that some of the evaporator sections 6 receive an insufficient amount of refrigerant to obtain an optimal filling degree. Accordingly, the potential refrigeration capacity of these evaporator sections 6, and thereby the overall potential refrigeration capacity of the evaporator 1, is not utilised to the full extent.
Fig. 3 shows an outlet manifold 7 for an evaporator. A pipe section 8 is arranged in an interior part of the outlet manifold 7. When the evaporator comprising the outlet manifold 7 is arranged in a refrigeration system, the pipe section 8 is fluidly connected between the condenser and the expansion device. Refrigerant leaving the evaporator tubes of the evaporator is collected in the outlet manifold 7 in the region 9 which is not occupied by the pipe section 8. Since the pipe section 8 is arranged in the interior part of the outlet manifold 7, the cool refrigerant leaving the evaporator tubes and the hot refrigerant leaving the condenser are allowed to exchange heat. Furthermore, the pipe section 8 is arranged in the interior part of the outlet manifold 7 in such a manner that the refrigerant leaving the evaporator tubes comes directly into contact with an outer surface of the pipe section 8, the refrigerant e.g. being sprayed directly onto the pipe section 8. Thereby the temperature of the refrigerant collected in the outlet manifold 7 is increased, preferably sufficiently to evaporate any liquid refrigerant which has passed through the evaporator tubes. Thereby it is possible to control the supply of refrigerant to the evaporator in such a manner that liquid phase refrigerant is present throughout the entire length of all, or at least most of, the evaporator tubes. Thereby the potential refrigeration capacity of the evaporator is utilised to the greatest possible extent. Even though liquid refrigerant is allowed to pass through some of the evaporator tubes, liquid refrigerant is not allowed to reach the compressor, since it is evaporated in the suction line heat exchanger formed by the pipe section 8 and the region 9 of the outlet manifold 7 which is not occupied by the pipe section 8.
It is an advantage that the suction line heat exchanger is accommodated directly in the outlet manifold 7, because the suction line heat exchanger can thereby be provided without the requirement of additional components. Thereby the manufacturing costs can be maintained at a low level, and a compact design is achieved. Furthermore, it is expected that the efficiency of the heat exchange in such an arrangement is good, since the liquid refrigerant leaving the evaporator tubes will be sprayed directly onto the pipe section 8 having the hot refrigerant flowing therein.
Fig. 4 shows an outlet manifold 7 for an evaporator. The interior part of the outlet manifold 7 is divided into three flow regions 10, 11, 12. In regions 10 and 11 a flow of hot refrigerant is present, and in region 12 cold refrigerant is received from the evaporator tubes. Thus, heat exchange takes place essentially as described above with reference to Fig. 3. However, in Fig. 4 the regions 10 and 11 are fluidly connected in such a manner that refrigerant leaving the condenser initially passes through region 10 and subsequently through region 11. The flow direction in each of the regions 10, 11, 12 is indicated by means of arrows. Thus, the hot refrigerant passes along the boundary towards region 12 twice, and the heat transfer area of the suction line heat exchanger is thereby increased. Accordingly, a more efficient heat transfer is obtained between the refrigerant flowing in regions 10 and 11 and the refrigerant flowing in region 12. Furthermore, multiple passages of hot and/or cold refrigerant in the suction line heat exchanger allow the heat exchange of the suction line heat exchanger to be designed, simply by arranging the hot/cold passages in an appropriate manner relative to each other.
Furthermore, a number of fins 13 are present in the region 12 receiving refrigerant from the evaporator tubes. Such fins 13 also increase the heat transfer area of the suction line heat exchanger, thereby improving the heat transfer between the hot refrigerant flowing in regions 10 and 11 and the cold refrigerant flowing in region 12. Furthermore, the fins 13 capture droplets of liquid refrigerant leaving the evaporator tubes and ensure that the liquid refrigerant is efficiently brought into direct thermal contact with the refrigerant flowing in regions 10 and 11.
In the embodiment illustrated in Fig. 4 the regions 10, 11, 12 are formed directly in the outlet manifold 7. This may, e.g., be done by means of an extrusion process. This makes the manufacturing process very easy and cost effective. Furthermore, the advantages described above relating to arranging the suction line heat exchanger in the outlet manifold 7 also apply to the embodiment shown in Fig. 4.
Fig. 5 shows an outlet manifold 7 for an evaporator. The interior part of the outlet manifold 7 is divided into four regions 10, 11, 12, 14. In regions 10 and 11 a flow of hot refrigerant received from the condenser is flowing, and in regions 12 and 14 refrigerant is received from the evaporator tubes. As it is the case in the embodiment shown in Fig. 4, regions 10 and 11 are fluidly connected in such a manner that refrigerant received from the condenser initially passes through region 10 and subsequently through region 11. Similarly, regions 12 and 14 are fluidly connected in such a manner that refrigerant received from the evaporator tubes initially flows through region 12 and subsequently through region 14. Due to the mutual arrangement of the regions 10, 11, 12, 14 heat exchange takes place between the refrigerant flowing in region 10 and the refrigerant flowing in region 12, and between the refrigerant flowing in region 11 and the refrigerant flowing in region 14. Thus, the design of the outlet manifold 7 shown in Fig. 5 in a sense prolongs the length of the flow path where heat exchange takes place to twice the length of the outlet manifold 7. Thus, the heat exchanging area, and thereby the heat transfer, is increased.
Similarly to the embodiment shown in Fig. 4, the regions 10, 11, 12, 14 shown in Fig. 5 are formed directly in the outlet manifold 7, e.g. by means of an extrusion process. As described above, this allows for an easy and cost effective manufacturing process. Finally, the remarks set forth above with reference to Fig. 3 regarding advantages obtained by arranging the suction line heat exchanger in the outlet manifold 7 are equally applicable in the embodiment illustrated in Fig. 5.
Fig. 6 illustrates a distribution of liquid and gaseous refrigerant delivered from five parallel evaporator tubes 2 to an outlet manifold 7. A secondary fluid flow across the evaporator is illustrated by arrow 19. In the situation illustrated in Fig. 6, the evaporator tubes 2 arranged closest to the incoming secondary fluid flow 19 deliver refrigerant in a substantially gaseous state to the outlet manifold 7. However, the evaporator tubes 2 arranged further away from the incoming secondary fluid flow 19 deliver refrigerant in a mixed or purely liquid state to the outlet manifold 7. Liquid refrigerant delivered from the evaporator tubes 2 is illustrated by a grey colour. The reason for the maldistribution of liquid and gaseous refrigerant described above is that the secondary fluid flow coming into contact with the first evaporator tubes 2 is warmer than the secondary fluid flow coming into contact with the last evaporator tubes 2. As a consequence, refrigerant flowing in the first evaporator tubes 2 is evaporated to a greater extent than refrigerant flowing in the last evaporator tubes 2.
Fig. 7 shows an outlet manifold 7 for an evaporator. The outlet manifold 7 of Fig. 7 is provided with a wall part 20 defining an interface between a flow region 10 in which a flow of hot refrigerant is present, and a flow region 12 in which the refrigerant leaving the evaporator tubes 2 of the evaporator is received. It can be seen from Fig. 7 that the wall part 20 is arranged in such a manner that the refrigerant leaving the evaporator tubes 2 and entering the flow region 12 is brought into direct contact with the wall part 20, and thereby into direct thermal contact with the hot refrigerant flowing in flow region 10. Thereby it is efficiently ensured that liquid refrigerant delivered from the flow tubes 2 and entering the flow region 12 is evaporated due to heat exchange with the hot refrigerant flowing in flow region 10. Accordingly, the flow regions 10, 12, the outlet manifold 7 and the wall part 20 in combination form a suction line heat exchanger.
The wall part 20 has a shape which is curved, defining a concave shape relatively to the flow region 10. Providing the wall part 20 with such a curved shape has the consequence that the wall part 20 is stronger than a wall part having the same material thickness, but which is not curved. Accordingly, the curved shape allows a given strength of the wall part 20 to be obtained with a smaller material thickness, thereby lowering the costs and the weight of the outlet manifold 7 without compromising the strength and the ability of the wall part 20 to withstand pressure differences between the flow regions 10, 12.
Fig. 8 shows an outlet manifold 7 for an evaporator. The outlet manifold 7 of Fig. 8 is very similar to the outlet manifold 7 of Fig. 7, and it will therefore not be described in detail here. In the outlet manifold 7 of Fig. 8 the wall part 20 has a curved shape, defining a convex shape relatively to the flow region 10. However, the advantages described above with reference to Fig. 7 are also obtained in the embodiment shown in Fig. 8.
Fig. 9 shows an outlet manifold 7 for an evaporator. The outlet manifold 7 of Fig. 9 is very similar to the outlet manifold 7 of Fig. 7, and it will therefore not be described in detail here. In the outlet manifold 7 of Fig. 9 the curved wall part 20 is arranged asymmetrically with respect to the positions of the flow tubes 2 of the evaporator. Thus, the wall part 20 is arranged closer to the outlet openings of the flow tubes 2 arranged furthest away from the incoming secondary fluid flow (reference numeral 19 in Fig. 6), than to the outlet openings of the flow tubes 2 arranged closest to the incoming secondary fluid flow. Accordingly, the wall part 20 is arranged close to the outlet openings where a large amount of liquid refrigerant is expected, and further away from the outlet openings where purely gaseous refrigerant is expected. Consequently, the droplets of liquid refrigerant delivered from the flow tubes 2 are caught by the wall part 2 immediately upon delivery to the outlet manifold 7, thereby efficiently ensuring that the liquid refrigerant is evaporated due to heat exchange with the hot refrigerant flowing in flow region 10. Furthermore, the liquid refrigerant delivered from the flow tubes 2 is prevented from mixing with the gaseous refrigerant delivered from the flow tubes 2 until it has been evaporated.
Fig. 10 shows an outlet manifold 7 for an evaporator. The outlet manifold 7 of Fig. 10 is very similar to the embodiment shown in Fig. 8, and it will therefore not be described in detail here. In the outlet manifold of Fig. 10 the curved wall part 20 is arranged asymmetrically with respect to the positions of the flow tubes 2 of the evaporator, similarly to the embodiment shown in Fig. 9. The advantages described above with reference to Fig. 9 are therefore also obtained in the embodiment shown in Fig. 10.
Fig. 11 shows an outlet manifold 7 for an evaporator. The outlet manifold 7 of Fig. 11 is very similar to the embodiment shown in Fig. 8, and it will therefore not be described in detail here. In the outlet manifold 7 of Fig. 11 three sectioning walls 21 have been arranged in abutment with the wall part 20. The sectioning walls 21 provide support for the wall part 20, thereby increasing the strength of the construction and enhancing the ability of the wall part 20 to withstand the pressure differences between the flow sections 10, 12. Furthermore, the hot side of the suction line heat exchanger is divided into four parallel flow regions 10. The parallel flow regions 10 may either simply divide the hot refrigerant into four parallel flows, or they may provide multiple passages of hot refrigerant as described above with reference to Figs. 4 and 5.
Fig. 12 shows an outlet manifold 7 for an evaporator. The outlet manifold 7 of Fig. 12 is very similar to the embodiment shown in Fig. 8, and it will therefore not be described in detail here. In the embodiment of Fig. 12 the wall part 20 has been provided with a number of fins 13 extending into the flow region 12. As described above with reference to Fig. 4, such fins 13 increase the heat transfer area of the suction line heat exchanger. Furthermore, the fins 13 separate the liquid refrigerant delivered by the flow tubes 2 arranged furthest from the secondary fluid flow across the evaporator (reference numeral 19 in Fig. 6) from the gaseous refrigerant delivered by the evaporator tubes arranged closest to the secondary fluid flow. Thereby the liquid refrigerant is prevented from mixing with the gaseous refrigerant until it has been evaporated due to heat exchange with the hot refrigerant flowing in the flow region 10.
Fig. 13 shows an outlet manifold 7 for an evaporator. The outlet manifold 7 of Fig. 13 is very similar to the embodiment shown in Fig. 12, and it will therefore not be described in detail here. In the embodiment of Fig. 13 the centre fin 13 is longer than the other fins 13. Thereby the refrigerant delivered by the first two flow tubes 2 is efficiently separated from the refrigerant delivered by the last two flow tubes 2. Thereby the separation of liquid and gaseous refrigerant is even more efficient. Furthermore, the centre fin 13 extends into the hot part of the suction line heat exchanger, thereby forming a sectioning wall 21 and dividing the hot part of the suction line heat exchanger into two flow regions 10 as described above with reference to Fig. 11.
Fig. 14 shows an outlet manifold 7 for an evaporator. The outlet manifold 7 of Fig. 14 is very similar to the embodiment shown in Fig. 9, and it will therefore not be described in detail here. However, in the embodiment shown in Fig. 14, the wall part 20 has been provided with four fins 13. The advantages described above with reference to Figs. 4, 12 and 13 are therefore also obtained for this embodiment. The fins 13 are only arranged on part of the wall part 20, i.e. the part where liquid refrigerant is expected to appear. Thus, the fins 13 efficiently catch the droplets of liquid refrigerant.
The fins 13 extend slightly into the flow region 10. Thereby the heat transfer in the flow region 10 is also improved. In some cases, this may be a limiting factor of the heat transfer of the suction line heat exchanger, e.g. in the case that liquid refrigerant which is not completely subcooled, e.g. a 'bubbly flow' or a 'slug flow', enters the flow region 10 of the suction line heat exchanger.
Fig. 15 shows an outlet manifold 7 for an evaporator. The outlet manifold 7 of Fig. 15 is very similar to the embodiment shown in Fig. 12, and it will therefore not be described in detail here. In the embodiment of Fig. 15 the fins 13 are only arranged on the part of the wall part 20 where liquid refrigerant is expected, and the fins 13 extend slightly into the flow region 10. The advantages described above with reference to Fig. 14 are therefore also obtained here.
Fig. 16 shows an outlet manifold 7 for an evaporator. The outlet manifold 7 of Fig. 16 is very similar to the embodiment shown in Fig. 15, and it will therefore not be described in detail here. However, in Fig. 16 the wall part 20 is curved in the manner shown in Fig. 7.
Fig. 17 shows an outlet manifold 7 for an evaporator. In the embodiment of Fig. 17 two pipe sections 8 are arranged in the flow region 12. Hot refrigerant is flowing inside the pipe sections 8 as described above with reference to Fig. 3. The pipe sections 8 are arranged inside the outlet manifold 7 in such a manner that refrigerant delivered by the flow tubes 2 is brought directly into contact with the pipe sections 8, and thereby directly into thermal contact with the hot refrigerant flowing in the pipe sections 8. The pipe sections 8 may provide parallel flow paths or multiple passages as described above with reference to Figs. 4 and 5.
Each of the pipe sections 8 is provided with a number of fins 13 in order to increase the heat transfer and catch the droplets of the liquid refrigerant as described above.
Fig. 18 shows an outlet manifold 7 for an evaporator. The outlet manifold 7 of Fig. 18 is similar to the embodiment shown in Fig. 17, in that two pipe sections 8 are arranged in the flow region 12, and in that hot refrigerant is flowing inside the pipe sections 8. A guiding wall 22 is arranged in the flow region 12 in such a manner that refrigerant delivered from the flow tubes 2 is initially brought into contact with the hot refrigerant flowing in the pipe section 8 arranged to the right in Fig. 18. The inlet manifold 7 is preferably designed in such a manner that the refrigerant is subsequently guided into contact with the pipe section 8 arranged to the left in Fig. 18. Thus, according to the embodiment shown in Fig. 18 the cool refrigerant passes along the length of the suction line heat exchanger twice, similarly to the situation described above with reference to Fig. 5.
Fig. 19 shows an outlet manifold 7 for an evaporator. In the outlet manifold 7 of Fig. 19 the hot side of the suction line heat exchanger is formed by three flow regions 10, each comprising four separate flow paths. This allows for multiple passages of the hot refrigerant and/or multiple parallel flows of hot refrigerant, thereby enhancing the heat transfer between the refrigerant flowing in the flow regions 10, 12.
Fig. 20 shows an outlet manifold 7 for an evaporator. The outlet manifold 7 of Fig. 20 is very similar to the embodiment of Fig. 19. However, in Fig. 20 the three flow regions 10 are not further divided into flow paths.
Fig. 21 shows an outlet manifold 7 for an evaporator. The outlet manifold 7 of Fig. 21 is similar to the embodiments of Figs. 19 and 20. However, in the embodiment of Fig. 21 the flow regions 10 have a pointed shape and they are arranged in the part of the outlet manifold 7 where liquid refrigerant is expected. The shape as well as the position of the flow regions 10 allows catching of droplets of liquid refrigerant delivered by the flow tubes 2 in a manner which ensures that the droplets are brought directly into thermal contact with hot refrigerant flowing in the flow regions 10, immediately upon delivery from the flow tubes 2 to the outlet manifold 7. The advantages of this have already been described above.
Fig. 22 shows an outlet manifold 7 for an evaporator. The outlet manifold 7 of Fig. 22 is very similar to the embodiment of Fig. 11, and it will therefore not be described in detail here. In Fig. 22 the wall part 20 is arranged asymmetrically with respect to the positions of the outlet openings of the flow tubes 2 of the evaporator, in the manner shown in Fig. 10. The advantages described above with reference to Fig. 10 are therefore also obtained here.
Fig. 23 shows an outlet manifold 7 for an evaporator according to the invention. In the outlet manifold 7 of Fig. 23 a wall part 20 is arranged in such a manner relatively to the flow tubes 2 of the evaporator that heat exchange takes place between refrigerant delivered by the flow tubes 2 and hot refrigerant flowing in flow region 10 before the refrigerant leaves the evaporator tubes 2. Thereby it is efficiently ensured that any liquid refrigerant passing through the evaporator is evaporated before leaving the outlet manifold 7.
Fig. 24 shows an outlet manifold 7 for an evaporator. A bent pipe section 8 is arranged in the outlet manifold 7 of Fig. 24, the bent pipe section 8 forming a flow path for hot refrigerant, the hot refrigerant passing the length of the suction line heat exchanger twice.
The outlet manifold 7 of Fig. 24 is further provided with an insert 23 arranged to guide refrigerant delivered by the outlet openings of the flow tubes 2 in such a manner that it is ensured that refrigerant delivered by the flow tubes 2 heat exchange with hot refrigerant flowing in the pipe section 8. If the insert 23 had not been present in the outlet manifold 7, there would have been a risk that refrigerant entering the outlet manifold 7 from the flow tubes 2 arranged furthest to the left in Fig. 24 would pass directly into the suction line of the vapour compression system without heat exchanging with the hot refrigerant flowing in the pipe section 8, because these flow tubes 2 are arranged very close to the outlet opening of the outlet manifold 7. However, the insert 23 guides the refrigerant towards the right in Fig. 24, thereby ensuring that the refrigerant flows along at least a part of the pipe section 8 before leaving the outlet manifold 7.
Fig. 25 shows an evaporator 1 comprising an inlet manifold 3 and an outlet manifold 7, and five evaporator tubes 2 arranged to fluidly connect the inlet manifold 3 and the outlet manifold 7. The outlet manifold 7 is of the kind shown in Fig. 3, i.e. it has a pipe section 8 arranged in an interior part thereof. It is clear from Fig. 6 that refrigerant from the evaporator tubes 2 is received at the region 9 of the outlet manifold 7 which is not occupied by the tube section 8.
Fig. 26 schematically illustrates the evaporator 1 of Fig. 25 arranged in a refrigerant path of a refrigeration system 15. Refrigerant is compressed in a compressor 16. The compressed refrigerant is passed through a condenser 17, and further on to an expansion valve 18, via tube section 8 arranged in the outlet manifold 7 of the evaporator 1. From the expansion valve 18 the refrigerant continues into the inlet manifold 3 of the evaporator 1. The inlet manifold 3 distributes the refrigerant among the parallel evaporator tubes 2, the refrigerant passes through the evaporator tubes 2 and is collected in the outlet manifold 7. From the outlet manifold 7 the refrigerant is once again fed to the compressor 16.
Since the refrigerant leaving the condenser 17 passes through the pipe section 8 arranged in the interior of the inlet manifold 7 before reaching the expansion valve 18, heat transfer takes place between the refrigerant flowing through the pipe section 8 and refrigerant entering the inlet manifold 7 from the evaporator tubes 2. Furthermore, the refrigerant entering the inlet manifold 7 is immediately brought into direct thermal contact with the hot refrigerant flowing in the pipe section 8, e.g. by spraying the refrigerant directly onto the pipe section 8. Thereby the temperature of the cold refrigerant leaving the evaporator tubes 2 is increased, thereby increasing the superheat of the refrigerant leaving the outlet manifold 7. Accordingly, if refrigerant leaving one or more of the evaporator tubes 2 contains liquid refrigerant, the heat transfer taking place in the outlet manifold 7 may be sufficient to evaporate the liquid refrigerant, thereby obtaining a positive superheat of the refrigerant leaving the outlet manifold 7. Furthermore, the direct thermal contact between the refrigerant flows described above provides a very efficient heat transfer. Thus, even though liquid refrigerant is allowed to pass through one or more of the evaporator tubes 2, it is prevented that liquid refrigerant reaches the compressor 16. Thereby it is possible to control the supply of refrigerant to the evaporator 1 in such a manner that liquid refrigerant is present throughout the entire length of all of the evaporator tubes 2, or at least of most of the evaporator tubes 2, without risking damage to the compressor 16. Thus, the overall potential refrigeration capacity of the evaporator 1 can be utilised to a greater extent than is the case in prior art refrigeration systems.
Furthermore, since the suction line heat exchanger is provided as a part of the outlet manifold 7 of the evaporator 1, the advantages described above are achieved without the requirement of additional components, and while maintaining a compact design of the refrigeration system 15.
It should be noted, that one of the outlet manifolds 7 shown in Figs. 4, 5 and 7-24 could alternatively be applied in the refrigeration system 15 of Fig. 26. Furthermore, any other suitable design of the outlet manifold 7 including a suction line heat exchanger could be applied without altering the principles of operation of the refrigeration system 15 shown in Fig. 26 and described above.
Fig. 27 is diagrammatic view of a refrigeration system 15. The refrigeration system 15 comprises an evaporator 1, a compressor 16, a condenser 17 and an expansion valve 18 arranged in a refrigerant path. The evaporator 1 is of a kind comprising at least two evaporator tubes (not shown) arranged fluidly in parallel between an inlet manifold (not shown) and an outlet manifold 7.
The outlet manifold 7 is provided with a suction line heat exchanger, thereby providing heat transfer between refrigerant leaving the evaporator tubes and entering the outlet manifold 7, and refrigerant flowing from the condenser 17 towards the expansion valve 18, as explained above. The suction line heat exchanger may, e.g., be provided in the manner described above with reference to any of Figs. 3-5 and Figs. 7-24. In the refrigeration system 15 of Fig. 27 the direction of the flow of the cold refrigerant is opposite to the direction of the flow of the hot refrigerant, i.e. Fig. 27 illustrates a 'counter-flow' situation.
Fig. 28 is a diagrammatic view of a refrigeration system 15. The refrigeration system 15 of Fig. 28 is very similar to the refrigeration system 15 of Fig. 27. However, in this case the direction of flow of the cold refrigerant is identical to the direction of flow of the hot refrigerant, i.e. Fig. 28 illustrates a 'co-flow' situation.
Fig. 29 is a diagrammatic view of a refrigeration system 15. The refrigeration system 15 of Fig. 29 also comprises an evaporator 1, a compressor 16, a condenser 17 and an expansion valve 18 arranged in a refrigerant path. The condenser 17 is provided with an outlet manifold 7. The outlet manifold 7 is provided with a suction line heat exchanger. Thus, refrigerant leaving the evaporator 1 is led through the suction line heat exchanger in the outlet manifold 7 of the condenser 17 before reaching the compressor 16. Accordingly, any liquid refrigerant which has been allowed to pass through the evaporator 1 can be evaporated before the refrigerant reaches the compressor 16, similarly to the situation described above with reference to Fig. 27. Furthermore, a compact design of the refrigeration system 15 can be maintained, since the suction line heat exchanger is provided in the outlet manifold 7 of the condenser 17.
The suction line heat exchanger may, e.g., be provided in the manner described above with reference to any of Figs. 3-5 and Figs. 7-24. In the refrigeration system 15 of Fig. 29 the direction of the flow of the cold refrigerant is opposite to the direction of the flow of the hot refrigerant, i.e. Fig. 29 illustrates a 'counter-flow' situation.
Fig. 30 is a diagrammatic view of a refrigeration system 15. The refrigeration system 15 of Fig. 30 is very similar to the refrigeration system 15 of Fig. 29. However, in this case the direction of flow of the cold refrigerant is identical to the direction of flow of the hot refrigerant, i.e. Fig. 30 illustrates a 'co-flow' situation.

Claims

An evaporator for a vapour compression system (15), the evaporator comprising:
- at least two evaporator tubes arranged fluidly in parallel, each flow tube comprising an inlet opening adapted to receive fluid medium and an outlet opening adapted to deliver fluid medium,

- an inlet manifold (3) arranged in fluid connection with the inlet opening of each of the evaporator tubes, thereby being adapted to distribute fluid medium among the evaporator tubes, and

- an outlet manifold (7) arranged in fluid connection with the outlet opening of each of the evaporator tubes, thereby being adapted to collect fluid medium delivered from each of the evaporator tubes,
wherein the outlet manifold (7) is provided with a suction line heat exchanger for fluidly interconnecting a refrigerant outlet of a condenser and a refrigerant inlet of an expansion device (18) of a vapour compression system,
and wherein the suction line heat exchanger being arranged in such a manner that direct thermal contact is provided between refrigerant delivered from the evaporator tubes and the suction line heat exchanger, and where the suction line heat exchanger comprises a wall part (20) defining an interface between a first flow region (10, 11) arranged to accommodate a heat exchanging fluid and a second flow region (12, 14) arranged to receive refrigerant delivered from the outlet openings of the evaporator tubes and entering the outlet manifold (7),
characterized in that said wall part (20) is arranged in the outlet manifold (7) in such a manner relatively to the flow tubes (2) of the evaporator that heat exchange takes place between refrigerant delivered by the flow tubes (2) and hot refrigerant flowing in flow region (10) before the refrigerant leaves the evaporator tubes (2).
An evaporator according to claim 1 , wherein the suction line heat exchanger forms an integral part of the outlet manifold (7).
An evaporator according to claim 1 , wherein the suction line heat exchanger forms a separate part inserted into the outlet manifold (7).
An evaporator according to any of the preceding claims, wherein the suction line heat exchanger is configured in such a manner that hot and/or cold fluid medium passes along the outlet manifold (7) at least two times.
An evaporator according to any of the preceding claims, wherein the flow tubes are in the form of microchannels.
An evaporator according to any of the preceding claims, wherein the outlet manifold (7) is or comprises an outlet header.
An evaporator according to any of the preceding claims, wherein the outlet manifold (7) and/or the suction line heat exchanger is/are shaped in a manner which separates liquid refrigerant delivered from the outlet openings of the flow tubes from gaseous refrigerant delivered from the outlet openings of the flow tubes.
An evaporator according to claim 7, wherein the suction line heat exchanger comprises one or more fins (13) extending into an interior part of the outlet manifold (7).
A evaporator according to claim 1 , wherein the wall part (20) has a curved shape.
A evaporator according to claim 1 or 9, wherein the wall part (20) is arranged asymmetrically with respect to the outlet openings of the flow tubes.