EP3009780A1 - Heat exchanger - Google Patents

Abstract

The invention relates to a heat exchanger (1) for cooling a heat source of a motor vehicle with a coolant channels (2) forming a coolant flow path (6) and refrigerant channels (3) forming a refrigerant flow path (7). Essential to the invention is that - the refrigerant is CO 2, - The refrigerant flow path (7) is deflected at least once U-shaped, the refrigerant channels (3) have a ratio between their wall thickness (w) and their diameter (d) of at least 0.4, - A between two refrigerant channels (3) existing web (5) has a width b, which is at least 40% of the diameter of the refrigerant channel (3), preferably even 70%, more preferably even 100% of the diameter of the refrigerant channel (3).

Description

The present invention relates to a heat exchanger for cooling a heat source of a motor vehicle with coolant channels and refrigerant channels according to the preamble of claim 1.

From the DE 10 2011 107 281 A1 a generic heat exchanger for cooling a heat source of a motor vehicle is known, comprising a plurality of refrigerant channels and a plurality of coolant channels. The coolant passages are formed by clearances provided between the refrigerant passages, wherein heat transferring surfaces are provided between a refrigerant guided in the refrigerant passages and a coolant guided in the coolant passages. In the area of the heat transfer surfaces, the refrigerant channels have a refrigerant-carrying volume which is larger by a factor between 4 and 6 than the coolant-carrying volume of the coolant channels in the region of the heat transfer surfaces. This is to achieve a so-called chiller with a compact design and a high heat exchange efficiency.

From the DE 10 2005 020 499 A1 a heat exchanger for a motor vehicle is known, which can be traversed by refrigerant. The flowing into the heat exchanger refrigerant flow is thereby divided by a valve device to at least two separate strands such that there is no mutual mixing of each inflowing refrigerant partial flow. This is to a uniform temperature distribution can be ensured.

In the steadily increasing segment of hybrid and electric vehicles, a particularly effective temperature management of high-voltage batteries is of central importance for the range extension and the efficient use of electrical energy. To cool the batteries while so-called "chiller" are used, which build compact. In order to increase the cooling capacity, CO ₂ is increasingly being used as a refrigerant, whereby, however, the systems must be designed for higher system pressures and temperatures. Previous plate heat exchangers for cooling a low-temperature circuit are not suitable for this purpose.

The present invention therefore deals with the problem of providing a heat exchanger of the generic type an improved or at least one alternative embodiment, which in particular allows efficient cooling with low weight and low cost of the heat exchanger.

This problem is solved according to the invention by the subject matter of independent claim 1. Advantageous embodiments are the subject of the dependent claims.

The present invention is based on the general idea of combining the advantages of an indirect evaporator (chiller) with the advantages of CO ₂ as the refrigerant and thereby to be able to provide a compact, high-efficiency and, on the other hand, inexpensive heat exchanger, in particular for battery cooling. The heat exchanger according to the invention thus serves for cooling a heat source, such as a high-voltage battery or an electronic component, in a motor vehicle and has in a known manner coolant channels and refrigerant channels. The individual refrigerant channels in a flat tube together with the adjoining refrigerant channels of the other flat tubes form a refrigerant flow path. In a similar way applies this also for the coolant channels, which lined up a coolant flow path. Of course, the coolant flows around the flat tubes. As refrigerant now carbon dioxide (CO ₂ ) is used, wherein the refrigerant flow on the one hand at least once is deflected U-shaped and the refrigerant channels also have a ratio between their wall thickness and their free diameter (inner diameter) of at least 0.4. Due to the at least unique U-shaped deflection, both the run length and the flow velocity can be increased and thus the heat transfer rate can be increased. Due to the comparatively high pressure and the associated small volume flows, the deflection on the refrigerant side is preferable, it being understood that a U-shaped deflection of the coolant flow path can be provided. In this case, a U-shaped flow path can be understood to mean a flow path that runs first in one direction and then after a 180 ° turn in the reverse direction, so that the refrigerant flows in opposite directions in the two flow path sections. Of course, a repeated reversal or redirection is possible. The refrigerant channels are positioned parallel to each other in so-called flat tubes, so that such a flat tube comprises a plurality of mutually parallel refrigerant channels. Between the individual flat tubes are the coolant channels, so that an outer wall of a respective flat tube simultaneously forms a wall of a coolant channel. Between the individual flat tubes, ie in the coolant channels, there may be heat transfer elements, such as turbulence inserts or corrugated fins, which improve heat transfer. In order to be able to form the refrigerant channels themselves wear-resistant over the long term against the comparatively high pressure, they are dimensioned such that the ratio of their wall thickness to the free diameter or the channel width is at least 0.4. A further requirement for the refrigerant channels according to the invention is that a web present between two refrigerant passages of a flat tube has a width which is at least 40% of the channel width, ie, the diameter of the refrigerant channel, preferably even 70 or even 100% of the (inner) diameter of the refrigerant channel. By such massive webs, it is easily possible to be able to record the pressures occurring in the refrigerant channels in the long term. With such a trained heat exchanger thus not only a compact heat exchanger can be achieved with a comparatively high heat transfer rate, but this can also be produced comparatively inexpensive, which is particularly in view of competition in the automotive supply sector of great advantage.

In an advantageous development of the solution according to the invention, the refrigerant channels and the coolant channels are arranged in sections, that is to say locally, in cross flow and in the entirety, that is to say globally, in countercurrent. A particularly favorable embodiment from the thermodynamic point of view arises when both the refrigerant flow path and the coolant flow path are deflected the same and thus a countercurrent or cross flow can be maintained over all paths. Since it is to be expected in a chiller in normal operation with an overheating of the refrigerant of about 5 Kelvin, it is advantageous if in particular the last section before the refrigerant discharge is in countercurrent. The countercurrent principle is used here because in the last flow often the refrigerant is already evaporated and only further heated, that is superheated. While there is no change in temperature during evaporation, the refrigerant heats up in the overheated area. Here, therefore, the power supply is of particular importance. Meaningful variants arise in particular when both the refrigerant side and the coolant side are deflected and both the coolant and the refrigerant in the respective flow path is in countercurrent. Here, a 2-, 4- or 6-flow current control is conceivable. If both the coolant side and the refrigerant side are deflected, both flow paths can also be in cross-flow, it being particularly useful here for the refrigerant to exit and to place the coolant inlet in the same section and thereby form a countercurrent characteristic globally. Again, the refrigerant side can be formed 4- or 6-flow.

In an advantageous development of the solution according to the invention, a hydraulic diameter of the refrigerant channels is between 0.3 and 1.0 mm. The hydraulic diameter is a calculated value which is used to calculate pressure loss and throughput in pipes and channels, provided that the cross section of the pipe or of the channel deviates from the circular shape. The hydraulic diameter is thus to be determined in particular for refrigerant channels whose cross-section is, for example, square with rounded corners or elliptical. The hydraulic diameter is for such channels thus the diameter of that circular channel, which would have the same pressure loss as the given channel at the same length and the same average flow rate. With the empirically discovered hydraulic diameter between 0.3 mm and 1.0 mm, both optimum pressure resistance and optimal heat transfer can be achieved. Particularly advantageous here are of course round or elliptical channels.

In a further advantageous embodiment of the solution according to the invention, the inner walls of the refrigerant channels are smooth, whereas the inner walls of the coolant channels are structured, ie in particular rough, in order to be able to achieve improved heat transfer. The improved heat transfer is generated by the larger surface. In addition, the edges of the component lead to a flow separation and thus to increased turbulence. Due to the high pressure load and the requirements on the internal cleanliness, however, a structured inside of the refrigerant channel does not make sense. In order to rule out any impairment of the circulation, purity requirements for all media-carrying parts exist for the components installed in the circuit.

For example, particles (tinsel, chips, etc.) are only tolerated up to a certain amount and consistency. For this, structurings on the inside make sense (for example if the flow channels have not round but star-shaped cross-sections.

Expediently, heat transfer elements, in particular turbulence inserts or corrugated fins, are arranged in the coolant channels. Such heat transfer elements increase the surface area available for heat transfer and thereby enable improved heat exchange.

Other important features and advantages of the invention will become apparent from the dependent claims, from the drawings and from the associated figure description with reference to the drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Preferred embodiments of the invention are illustrated in the drawings and will be described in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components.

Fig. 1

einen erfindungsgemäßen Wärmeübertrager mit umgelenkten Kältemittel- und Kühlmittelkanälen,

Fig. 2

eine Schnittdarstellung durch ein Flachrohr mit erfindungsgemäß ausgebildeten Kältemittelkanälen,

Fig. 3

eine Darstellung wie in Figur 2, jedoch mit anderen Kältemittelkanälen,

Fig. 4

einen erfindungsgemäßen 4-flutigen Wärmeübertrager im Kreuzstrom und zusätzlicher Umlenkung in der Tiefe,

Fig. 5

einen 2-flutigen Wärmeübertrager im Kreuzstrom sowohl kühlmittelseitig als auch kältemittelseitig und Umlenkung in der Breite,

Fig. 6

einen erfindungsgemäßen Wärmeübertrager im Gegenstrom einer kältemittelseitigen Umlenkung in der Breite,

Fig. 7

einen Wärmeübertrager im Gegenstrom mit kühl- und kältemittelseitiger Umlenkung,

Fig. 8

einen als Verdampfer ausgebildeten Wärmeübertrager mit vorgeschaltetem Expansionsorgan.

Show, in each case schematically,

Fig. 1

a heat exchanger according to the invention with deflected refrigerant and coolant channels,

Fig. 2

a sectional view through a flat tube with inventively designed refrigerant channels,

Fig. 3

a representation like in FIG. 2 but with other refrigerant channels,

Fig. 4

a four-flow heat exchanger according to the invention in the cross-flow and additional deflection in the depth,

Fig. 5

a two-flow heat exchanger in cross-flow both coolant side and refrigerant side and deflection in the width,

Fig. 6

a heat exchanger according to the invention in countercurrent to a refrigerant-side deflection in the width,

Fig. 7

a heat exchanger in countercurrent with cooling and refrigerant side deflection,

Fig. 8

designed as an evaporator heat exchanger with upstream expansion element.

According to the FIGS. 1 and 4 to 8, has a heat exchanger 1 according to the invention for cooling a heat source of a motor vehicle, in particular for cooling a heat pump or a high-voltage battery or an electronic component, coolant channels 2 and 3 refrigerant channels. According to the invention, carbon dioxide (CO ₂ ) is used as the refrigerant in all heat exchangers 1 and, moreover, a refrigerant flow path 7 is deflected at least once in a U-shaped manner. Due to the at least unique U-shaped deflection of at least the refrigerant flow path 7, the efficiency and also the performance of the heat exchanger 1 according to the invention can be significantly increased. Since CO _{2 is used} as refrigerant and comparatively high pressures occur, Moreover, according to the invention, the refrigerant channels 3 have a ratio between their wall thickness w and their diameter d of at least 0.4 (cf. FIGS. 2 and 3 ). Due to the high pressure in the refrigerant channels 3 and the associated small volume flows, a deflection on the refrigerant side is preferable.

The individual refrigerant channels 3 are arranged parallel to each other in flat tubes 4, wherein a web 5 present between two refrigerant channels 3 has a width b which is at least 40% of the diameter of the refrigerant channel 3, preferably even 70 or 100% of the diameter of the refrigerant channel 3 (again the FIGS. 2 and 3 ). Such thick webs 5 ensure the required tensile strength. Of course, it is conceivable that the individual refrigerant channels 3 are connected evenly or progressively. In this case, progressive means that the flow cross-sectional area of the refrigerant side increases from one flow path to the next. As a result, the increasing volume of the refrigerant flow during evaporation is taken into account. This does not affect the geometric shape of the individual refrigerant channels 3 in the respective flat tube 4, but is set by the number of flat tubes 4 per flow path 6, 7.

In order to ensure the required high compressive strength per se, the refrigerant channels 3 are preferably round or elliptical (see. FIG. 3 ), but may also have a square cross-section with rounded corners, as for example according to the FIG. 2 is shown.

Considering the heat exchanger 1 according to the FIG. 1 2, it can be seen that it operates in cross flow, so that a coolant flow path 6 flows substantially orthogonal to the refrigerant flow path 7. Of course, alternatively, the design as a countercurrent cooler is conceivable. Since in a heat exchanger 1 (chiller) in normal operation with an overheating of Refrigerant is expected to be about 5 Kelvin, it is also advantageous if in particular the last section before the refrigerant discharge is in countercurrent.

Looking at the individual flow paths 6, 7 in the heat exchanger 1 according to the FIG. 1 Thus, it can be seen that both the refrigerant flow path 7 and the coolant flow path 6 are deflected, resulting in a particularly effective cooling. The refrigerant and the coolant, for example a water-glysantin mixture, are in both flow paths 6, 7 in the cross flow, as well as in the heat exchanger 1 according to Figures 4 and 5. Here, it is particularly useful to the refrigerant outlet and the coolant inlet to lay the same section, where of course the refrigerant side can also be performed 4- or 6-flow.

The heat exchanger 1 according to the FIG. 5 It works in cross-flow and is 2-flow, both refrigerant side and coolant side and each has a deflection of the coolant flow path 6 and the refrigerant flow path 7 in width. The heat exchanger 1 according to the FIG. 4 is formed four-flow and has one compared to that according to the FIG. 5 Heat exchanger 1 shown a higher flow velocity through which the heat transfer is improved. Due to the 4-flood training also a better protection against overheating can be guaranteed.

In principle, the refrigerant channels 3 are taken in one or two collectors 8, in which a channel height h in relation to the material thickness w ₁ (wall thickness of the collector 8) is a maximum of 3, better even less than 1.5. Such a collector 8 is for example in the FIGS. 6 and 7 shown.

In order to ensure a sufficient heat transfer and sufficient pressure resistance, there is a hydraulic diameter d _{H of} the refrigerant channels 3 between 0.3 and 1.0 mm. A comparable hydraulic diameter d _H for the coolant channels 2 is preferably between 0.5 and 2.0 mm. As a result, an optimal ratio of pressure drop and heat transfer can be achieved on the coolant side. A particularly advantageous ratio between the hydraulic diameter of the coolant channels 2 and the hydraulic diameter of the refrigerant channels 3 is greater than 1.0, preferably this ratio is between 1.5 and 3. On the refrigerant side, usually a two-phase mixture is heated, which usually too significantly worse heat transfer coefficient on the refrigerant side than on the coolant side leads. In order to heat the refrigerant efficiently and thus to be able to cool the coolant efficiently, high heat transfer surfaces and small hydraulic diameters on the refrigerant side have to be realized. On the coolant side, however, there is a very good heat transfer, but on the coolant side, a lower pressure drop is desirable.

In order to be able to additionally improve a heat transfer, heat transfer elements 9, for example turbulence inserts or corrugated fins, which increase the surface available for heat exchange, are arranged in the coolant channels 2. Of course, also the heat transfer available surface can be structured, which in turn increases the surface. Due to the high pressure load and the requirement for internal cleanliness, a structured surface for the refrigerant side, i. H. Concrete for the inner circumferential surface of the refrigerant channels 3, however, not suitable.

Finally, considering the heat exchanger 1 according to the FIG. 6 , so here is the refrigerant flow path 7 at least once deflected in a U-shape and indeed in width, wherein the coolant flow path 6 can be deflected in corresponding coolant headers 10. The coolant flow path 6 and the refrigerant flow path 7 run in countercurrent.

In the heat exchanger 1 according to the FIG. 7 takes place both a U-shaped deflection of the coolant flow path 6 and a U-shaped deflection of the refrigerant flow path 7, each 2-flow, in which case the flow in countercurrent. Since countercurrent losses of heat-transferring surface must be taken into account, a cross-flow is here in principle to be preferred.

When countercurrent in the flow direction distribution channels must be introduced, whereas the cross flow is structurally simpler, but not very good in terms of efficiency and response to overheating. It is best for very compact heat exchanger therefore a combination in which although the individual sections are operated in cross-flow, but these are arranged (at least proportionally) in succession to the countercurrent principle.

According to the Fig. 8 is a trained as R744 evaporator heat exchanger 1 shown with an upstream expansion element 11. The expansion element 11 can be designed, for example, as an electronic expansion valve (EXV). This expansion element 11 was typically grown on conventional R134a evaporators. For R744 and also for components with electronic expansion valve (EXV), however, these are usually integrated separately from the heat exchanger 1 in the circuit. If the expansion element 11 is installed in assembly with the evaporator, there are cost advantages, advantages in handling and possibly advantages in the interfaces. The term "unit" is to be understood that the expansion element 11 (in particular TXV) is mechanically (possibly even cohesively) connected to the evaporator / chiller. Such an assembly could, for example, by an integration of the valve housing in the evaporator / chiller flange (+ possibly a Mitlöten) take place.

With the heat exchanger 1 according to the invention can be a high performance, ie achieve high efficiency of the heat exchanger 1, with low space requirements and favorable connection situation, especially if a connection arranged both for the coolant flow path 6 and the refrigerant flow path 7 on the same side of the heat exchanger 1 are. In addition, a high pressure resistance can be ensured by the refrigerant channels 3 designed according to the invention, which enables the use of CO ₂ as the refrigerant.

Claims (11)

Heat exchanger (1) for cooling a heat source of a motor vehicle with a coolant flow path (6) forming coolant channels (2) and a refrigerant flow path (7) forming refrigerant channels (3),
characterized in that - the refrigerant is CO ₂ , - The refrigerant flow path (7) is deflected at least once U-shaped, the refrigerant channels (3) have a ratio between their wall thickness (w) and their diameter (d) of at least 0.4, - A between two refrigerant channels (3) existing web (5) has a width b, which is at least 40% of the diameter of the refrigerant channel (3), preferably even 70%, more preferably even 100% of the diameter of the refrigerant channel (3). Heat exchanger according to claim 1,
characterized in that
the coolant flow path (6) is deflected at least once in a U-shape. Heat exchanger according to claim 1 or 2,
characterized in that
the refrigerant channels (3) have a square cross-section with rounded corners. Heat exchanger according to claim 1 or 2,
characterized in that
the refrigerant channels (3) are round or elliptical. Heat exchanger according to one of claims 1 to 4,
characterized in that
the refrigerant channels (3) are held in a collector (8), the collector (8) having distribution channels in which h / w ₁ <3.0, in particular h / w ₁ <1.5 (h height of the distribution channel / Collector; w ₁ wall thickness of the collector). Heat exchanger according to one of claims 1 to 5,
characterized in that
the refrigerant channels (3) and the coolant channels (2) are arranged in sections in cross-flow and in the totality in countercurrent. Heat exchanger according to one of claims 1 to 6,
characterized in that
in the coolant channels (2) heat transfer elements (9), in particular turbulence inserts or corrugated fins, are arranged. Heat exchanger according to one of claims 1 to 7,
characterized in that - A hydraulic diameter d _{h of} the refrigerant channels (3) is 0.3 mm <d _h <1.0 mm. - A hydraulic diameter d _{h of} the coolant channels (2) is 0.5 mm <d _h <2.0 mm. Heat exchanger according to one of claims 1 to 8,
characterized in that
a refrigerant flow path (7) is formed progressively. Heat exchanger according to one of claims 1 to 9,
characterized,
that the distance between two refrigerant channels (3)-making flat tubes (4) constitutes a maximum coolant channel height of 3.5mm. Heat exchanger according to one of claims 1 to 10,
characterized,
that the heat exchanger (1) is designed as evaporator and integrally with an upstream expansion member (11), in particular an electronic expansion valve (EXV) is executed.

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