EP0132620B1 - Evaporator - Google Patents

Description

The invention relates to an evaporator, in particular for air conditioning systems of motor vehicles, according to the preamble of claim 1.

Such evaporators are known (US-A-2 787 138). In these known designs, a swirling element in the form of a Venturi nozzle with downstream constrictions is provided. This nozzle is flowed through axially and, due to the changes in diameter of the flow channel, can cause a certain swirling of the medium flowing through. The disadvantage is that such a mixing element requires a relatively large axial length, which is not always available.

In cramped installation conditions, for example in motor vehicles, it is not possible to realize such axial lengths. It is also not possible, because of the sealing problems on the evaporator housings, to install the flow distributor immediately behind the expansion valve, as a result of which an at least somewhat satisfactory distribution of the refrigerant flow could be achieved. Rather, it is necessary to use curved or spatially wound connecting lines between the expansion valve and the flow distributor. Under these conditions, due to the different inertia of the refrigerant vapor and the refrigerant liquid, the two phases are separated and swirl flows are formed, which could not be safely avoided by connecting a Venturi tube. Since these asymmetrical swirl flows are divided into circular segments by the flow distributor, some of the evaporator tube strands are flooded with refrigerant liquid, while other strands are predominantly filled with gas and participate only little in the heat exchange. The efficiency of the evaporator deteriorates significantly. In addition, the evaporator performance is reduced by the control properties of thermostatic expansion valves.

Although it is also known (US _- A-2182664) cylindrical form a distributor for the refrigerant, the refrigerant introduced axially into these cylindrical distributor and at the same height arranged symmetrically distributed on the circumference pipes dissipate again. With such a distributor it is indeed possible to make the partial streams of the same size; however, the problem of partial separation of the liquid and the gaseous phase of a refrigerant flowing through curved connecting lines cannot be solved. An uneven distribution of the phases in the axial inflow provided there also remains in the outflow into the radially outgoing lines.
The present invention is therefore based on the object of ensuring, in the case of an evaporator of the type mentioned at the outset, that despite curved or tortuous connecting lines between expansion valves) and flow distributor, there is a homogeneous wet steam flow at the flow distributor.

This object is achieved by the characterizing features of patent claim I. Through this configuration, intensive swirling and mixing is achieved directly in front of the flow distributor. The broadening of the flow cross-section causes the two-phase flow consisting of refrigerant vapor and refrigerant liquid to burst, so that these two phases can be swirled intensively as they continue to flow through the vortex drum. This effect is also supported by the impact of the liquid particles on the cylinder wall opposite the inlet opening. There is no additional connecting line between the vortex drum and the flow distributor.

The entry of the wet steam flow in the standing slightly to a lower pressure level, designed as a vortex drum Verwirbelun ^g s-element takes place adiabatically, ie without the supply of heat from the environment. The evaporator output is therefore not reduced by the configuration according to the invention. It can also be assumed that the low pressure drop in the swirling element does not impair the function and performance of the expansion valves already used. Finally must also remember the Fertigungsqtjalität - apart from the at Kälteanlägen übli _- chen demands for compressive strength, density and purity - no special demands are made so that the evaporator according to the invention without additional costs with respect to known evaporators is produced. The simple manufacturing possibility of the vortex drum also makes itself felt here.

An advantageous application of the invention is in evaporators, in which the refrigerant connections must be on a certain evaporator side. Since the suction lines, i.e. the lines for discharging the refrigerant vapor, are on the other side of the evaporator, it follows that an odd number of tubes is always used for each evaporator jet. It now happens that the number of evaporator lines, ie the number of refrigerant injections, is even, which would in itself require an even number of pipes in the evaporator block. However, the evaporator blocks are often designed to contain an odd number of tubes. In this case, an empty pipe remains.

An example should explain this: An evaporator block comprises 9 tubes in width and 5 tubes in depth, for a total of 45 tubes. The refrigerant injection is designed fourfold, resulting in four evaporator lines. Each of these evaporator lines now has 11 tubes, so that 4 x 11 = 44 tubes are required. The 45th pipe remains as an empty pipe.

Due to the high gas speeds and the associated high pressure drop Mostly, the suction line to the compressor, which removes the refrigerant vapor, cannot be routed through the empty pipe in the evaporator to the connection side of the evaporator. With the invention, however, it is possible to use this empty pipe as a connecting line between the expansion valve and flow distributor. The expansion valve is therefore located on the side of the evaporator block facing away from the connection side, the empty tube connecting this expansion valve to the connection side. A swirling element according to the invention is then arranged on the connection side, which ensures a homogeneous wet steam flow in front of the flow distributor. This does not reduce the evaporator output.

With this design, not only the empty pipe in the evaporator block is used, but at the same time the routing of an evaporator connection line around the evaporator block is avoided, which is difficult or impossible to achieve, particularly in the case of limited space.

• Fig. 1 die Anordnung eines Verdampfers mit einer zur Erzielung einer homogenen Nassdampfströmung dem Strömungsverteiler vorgeschalteten Beruhigungsstrecke, wie sie jedoch unter beengten Einbauverhältnissen nicht realisiert werden kann,
• Fig. 2 eine andere Anordung eines Verdampfers, die jedoch aufgrund von Abdichtproblemen am Verdampfergehäuse ebenfalls nicht zweckmässig ist,
• Fig. 3 eine dem Stand der Technik entsprechende Anordnung des Verdampfers mit gebogener und/oder gewundener Verbindungsleitung zwischen dem Expansionsven_til und dem Strömungsverteiler,
• Fig. 4 bis 6 vergrösserte Querschnitte durch die Verbindungsleitung zwischen Expansionsventil und Strömungsverteiler nach Fig. 3 gemäss den Bezu^gslinien IV-IV, V-V und VI-VI,
• Fig. 7 die prinzipielle Anordnung eines erfindungsgemässen Verdampfers,
• Fig. 8 einen Schnitt durch ein erfindungsgemässes Verwirbelungselement,
• Fig. 9 einen Querschnitt durch die Darstellung der Fig. 8 entlang der Bezugslinie IX-IX, und
• Fig. 10 die schematische Ansicht einer Anwendung des erfindungsgemässen Verwirbelungselementes bei einem Verdampfer mit ungerader Rohrzahl und gerader Zahl der Verdampferstränge.

Further features and advantages of the invention result from the description of the drawing, in which an embodiment of the invention is shown. Show it:

• 1 shows the arrangement of an evaporator with a calming section upstream of the flow distributor in order to achieve a homogeneous wet steam flow, but this cannot be achieved under cramped installation conditions,
• 2 shows another arrangement of an evaporator, which, however, is also not practical due to sealing problems on the evaporator housing,
• Fig. 3 a prior art arrangement of the evaporator with a curved and / or spiral connecting line between the expansion Sven _t il and the flow distributor,
• FIGS. 4 to 6 are enlarged cross-sections of the connecting line between the expansion valve and flow divider according to Fig. 3, in accordance with the Bezu ^g slinien IV-IV, VV and VI-VI
• 7 shows the basic arrangement of an evaporator according to the invention,
• 8 shows a section through a swirling element according to the invention,
• Fig. 9 is a cross section through the representation of Fig. 8 along the reference line IX-IX, and
• 10 shows the schematic view of an application of the swirling element according to the invention in an evaporator with an odd number of tubes and an even number of evaporator branches.

In Fig. 1, 1 denotes an expansion valve. The refrigerant flow enters this expansion valve in the direction of arrow A. The expansion valve is a thermostatic expansion valve in which the superheating of the refrigerant vapor in the evaporator tubes is used as a control variable for the charge control. Via a calming section 2, this expansion valve is connected to a flow distributor 3, which divides the refrigerant flow symmetrically. In particular, a flow distributor is used here, which divides the coolant flow into circular segments. Such a flow distributor is, for example, the Venturi distributor known from US Pat. No. 2,803116. In this case, the calming section 2 fulfills the task of ensuring a homogeneous wet steam flow or a central ring flow upstream of the flow distributor 3, so that each of the evaporator branches is allocated a flow of refrigerant with the same properties by the flow distributor 3.

The outputs of the flow distributor 3 are connected to the evaporator block 4. This evaporator block has a number of evaporator tubes. Several of these evaporator tubes are combined to form an evaporator tube string, so that each of the partial refrigerant flows originating from the flow distributor 3 flows through the evaporator block 4 several times. The aim is for the refrigerant to evaporate completely at the end of all evaporator lines and to be overheated by an amount that is the same in all lines. This overheating is then used again as a control variable for the filling control by the expansion valve 1. The refrigerant vapor then leaves the evaporator block in the direction of arrow B and is supplied to the compressor in a manner not shown here via a suction line.

It can be seen that a uniform evaporation and overheating of the refrigerant in the evaporator block is only guaranteed if there is a homogeneous wet steam flow in front of the flow distributor 3 or - in the case of division into circular segments - a centric ring flow. This task is taken over by the calming section 2 in the arrangement of FIG. 1. In the case of cramped installation conditions, for example in motor vehicles, it is not possible to implement a calming section of this type which, in practical use, is not designed to be horizontal, as shown here, but rather to rise or fall vertically. It is therefore necessary to look for other solutions.

An arrangement similar to that of FIG. 1 is shown in FIG. 2. Here, in view of the fact that behind the expansion valve 1 there is also an at least approximately homogeneous wet steam flow, a calming section has been dispensed with. However, such an arrangement is also not possible due to sealing problems on the evaporator housings in practical use.

FIG. 3 shows an arrangement of the evaporator corresponding to the prior art in the case of cramped installation conditions. Here, the refrigerant enters the expansion valve 1 in the direction of arrow A and is fed from there to the flow distributor 3 via a multiply bent or winding line 5. The line 5 can no longer function as a load Take over calming distance, as from Figures 4 to 6, the cross sections in the direction of the reference line IV-IV, VV and VI-VI of Figure 3; is shown. As can be seen from FIG. 4, there is still a homogeneous wet steam flow or a central ring flow directly behind the expansion valve 1. When passing through the multiply bent or winding line 15, however, swirl flows are formed; viielche, as can be seen from Fig. 5, result in an eccentric ring flow. There is therefore no longer a homogeneous mixture of refrigerant vapor and refrigerant liquid over the entire cross section. If, as shown in FIG. 6, this eccentric ring flow is now divided into circular segments by the flow distributor 3, the individual evaporator branches are no longer subjected to a uniform supply of refrigerant vapor or refrigerant liquid. For clarification, the supply lines A to F corresponding to the circle segments of FIG. 6 to the evaporator stock are also entered in FIG. 3. The result of this is that the damper line labeled D is subjected to a great deal of wet steam, while the other evaporator lines receive correspondingly less wet steam. In the arrangement shown, the least amount of wet steam is obtained from the evaporator branch A. The division into wet steam or gas is shown in FIG. 3 using the example of the evaporator branch A. The wet steam is designated 6 and the gas 7.

The inhomogeneous distribution of the refrigerant flow among the individual evaporator tube strands leads to two major disadvantages. Firstly, the efficiency of the evaporator deteriorates. On the other hand, the refrigerant vapor is not evenly overheated when it leaves the evaporator tube strands, which leads to unsatisfactory regulation of the thermostatic expansion valve 1:

The invention therefore proposes to arrange a swirling element with an expanding flow cross-section directly in front of the flow distributor. Such an arrangement is shown in principle in FIG. 7. The reference numbers of the previous figures have been retained. The cross-sectional expansion of the swirling element 8 arranged in front of the flow distributor 3 leads to a violent swirling of refrigerant vapor and refrigerant liquid and therefore to a homogeneous mixture. The flow distributor can now divide the refrigerant flow into similar refrigerant substreams that are fed to the individual evaporator tube strands. Evaporation and overheating therefore occur evenly in all evaporator tube strands, which results in an increased efficiency of the evaporator and at the same time better regulation of the expansion valve. The entry of the wet steam flow into the swirling cell, which is at a slightly lower pressure level, and the associated swirling is adiabatic, i.e. without heat from the surroundings; the evaporator output is therefore not reduced by the installation of such a swirling element. The low pressure drop in the swirling element at the same time does not impair the function and performance of the expansion valves already used.

An exemplary embodiment of the swirling element 8, which is only indicated schematically in FIG. 7, is shown in FIG. 8. The vortex air element is designed as a cylindrical vortex cell 9. An inlet opening 11 for the refrigerant flow is arranged on the cylinder jacket 10 of this vortex cell 9. The diameter d _{E of} this inlet opening 11 is chosen to be smaller than the diameter d _{w of} the vertebral cell 9, the ratio d _{E /} d _W preferably being between 1/2 and. This results in an expansion of the flow cross-section, which leads to a bursting of the two-phase flow consisting of refrigerant vapor and refrigerant liquid and therefore to a violent swirling or to the formation of a homogeneous mixture. Since the inlet opening 11 is arranged on the cylinder jacket, the two-phase flow also strikes the container wall opposite the inlet opening, which further promotes swirling. No special demands have to be made on the manufacturing quality of this vortex cell, apart from the usual requirements for refrigeration systems, such as pressure resistance, tightness and cleanliness.

The outlet opening 12 is also arranged on the cylinder jacket 10. The effective distance L between the inlet opening 11 and the outlet opening 12 is preferably 25 to 35 mm. In order to achieve a simple construction, the flow distributor 13 shown here as a component is inserted directly into the outlet opening 12. The outlay on components and assembly is hereby further reduced and the manufacture of an evaporator according to the invention becomes cheaper.

8 shows the cross section in the direction of the reference line IX-IX of FIG. 9. Here, the inlet connector 14 placed on the inlet opening 11 can be seen. This inlet connector 14 can be arranged as desired on the cylinder jacket 10, as indicated by the angle a, which can be between 0 and 360 °. The inlet opening can thus be adapted to the respective installation conditions.

A specific application of the invention is shown in FIG. 10. As is known, the case occurs frequently that an evaporator block is equipped with an odd number of tubes, while the number of evaporator tube strands and thus also the number of tubes required is even. In this case, an empty pipe in the United remains _- steam block left. This empty pipe cannot be used as a suction line to the compressor because of the high gas speeds and the associated high pressure losses. However, the invention makes it possible to use this empty pipe as a connecting line between the expansion valve and the flow distributor. A separate and sometimes evaporator connection line around the evaporator block, which is difficult or impossible to accommodate, is therefore eliminated.

10, the refrigerant flows in the direction of arrow A through the expansion valve 1 and is fed via a connecting line 21 to the empty pipe 22, which is only shown in broken lines. On the connection side of the evaporator block 23, this empty tube 22 opens into the swirling element, which is designed here as a swirl cell 24, as a result of which a homogeneous wet steam flow is produced again. After leaving the flow distributor 25 placed on the swirl cell 24, the refrigerant partial flows 26a to 26d, which are only shown schematically, are then fed to the evaporator tube strands. After passing through these strands, the refrigerant vapor passes through the suction line 27 in the direction of arrow B to the compressor, not shown here.

Claims (3)

1. Evaporator in particular for air conditioning systems of motor vehicles with an evaporator block with several evaporator pipes and e feeding device for the coolant, which consists of an expansion valve and a flow divider (13) dividing the coolant flow which is situated on an outlet opening of a vortex unit (8) located in front, whereby the connecting line between the expansion valve and flow divider is at least in part curved or wound, characterised in that the vortex unit (8) is constructed as a vortex drum (9), on the cylinder wall (10) of which the inlet opening (11) is located at an axial distance (L) to the outlet opening (12) and that the ratio of the diameters (d_E) to (d_w) of the entry opening (11) and the vortex drum (9) is at least ¹/₂ and at the most ²/₃, so that the flow cross section in the direction of the coolant flow is extended in a discontinuous manner.

2. Evaporator in accordance with claim 1, characterised in that the outlet opening (12) is located in the cylinder wall (10) of the vortex drum (9) and that the flow divider (13) extends away radially from this cylinder wall (10).

3. Evaporator in accordance with one of claims 1 or 2, characterised in that the connection between the expansion valve (1) and the vortex drum (9) is run through one of the pipes (22) of the evaporator block (23).

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