FR3096767A1 - DEFLECTION THERMAL EXCHANGER - Google Patents

Abstract

The invention relates to a heat exchanger (10) comprising a first and a second stage (E1, E2) separated by a transverse plate (20), each stage allowing the circulation of a fluid (14, 16), configured so that the first and the second fluid (14, 16) intersect in an exchange zone (12), one of the stages comprising, upstream of the exchange zone, a distribution zone ( 24) which has a deflection zone (27). The distribution zone has three distinct parts (A, B, C): - a first part (A), located upstream of the deflection point, comprising two fins with constant direction, - a second part (B), located at the 'location of the deflection zone (27) of the fluids (14, 16), comprising two main deflectors (28) having a deflection angle (β), - a third part (C) comprising two main deflectors (28) and two secondary deflectors (30) interposed between them. Figure for the abstract: figure 2

Description

DEFLECTION HEAT EXCHANGER

Field of invention

The present invention relates to the field of heat exchangers, in particular fluid-fluid exchangers of the “plate and fin” type for aircraft turbine engines.

State of the art

Due to the strong constraints in terms of mass and compactness at iso-performances (efficiency / pressure drops) in the field of aeronautics, exchangers are conventionally counter-current or cross-current exchangers whose heart has a series exchange surfaces of the “plates and fins” type. The plates make it possible to separate the flows: on one side the hot flow and on the other side of the plate, the cold flow. It is through these plates that most of the heat exchange takes place. The fins, on the other hand, make it possible to increase the exchange surface of these plates. This is why we speak of plates and fins. By analogy with heat transfer and electricity, we speak of “thermal resistance”. This analogy is commonly used to analyze heat exchangers. In usual practice, the heat flux and the temperature difference are linked by a thermal resistance (analogous to Ohm's law in electricity).

In a way that is well known per se, a “plate and fins” type exchanger 10 is an exchanger whose core 12 (or exchange zone) is organized in stages, as illustrated in FIG. 1. Two fluids 14, 16 s flowing in a general direction imposed by fins 18 forming ducts intersect on either side of transverse plates 20. The heat is transferred from the fluid at the highest temperature to the plates and fins by thermal conduction. This heat is then, in turn, transferred to the lower temperature fluid and vice versa.

It is thus known that for exchangers comprising an exchange zone with two flows (cold and hot) in counter-current, it is necessary to deflect at least one of the two flows entering and leaving the core (or exchange zone ) to ensure their separation. The zone where this deflection is located is located between the inlet/outlet and the core (or exchange zone) of the exchanger. This area is called the distribution area.

Known issues related to this distribution area are:

- the deflection of the flow leads to a significant pressure drop and areas of recirculation of the fluid, this hinders the homogeneous distribution of the flow and has negative consequences on the aerothermal and thermomechanical criteria of the exchanger,
- This distribution zone does not contribute optimally to the heat exchange (which is the main function of the exchanger) and therefore leads to a troublesome excess mass.

Purpose of the invention

The object of the present invention is in particular to provide a heat exchanger making it possible to improve, in a simple and effective manner, a homogeneous distribution of the flow of the flow deflected in the heart of the exchanger by limiting the pressure drop while limiting the size and therefore the mass of said exchanger.

This objective is achieved in accordance with the invention thanks to a heat exchanger for a turbomachine, comprising at least a first and a second stage separated by a transverse plate, each stage allowing the circulation respectively of a first fluid and of a second fluid, the exchanger being configured so that the first and the second fluid each circulate in its stage and intersect in an exchange zone, at least one of the first and of the second stage further comprising, upstream of the exchange zone in the direction of circulation of the first fluid, a distribution zone, the distribution zone comprising a deflection zone for the first fluid. The exchanger is characterized in that the distribution zone has three distinct parts:

- a first part, located upstream of the deflection point, comprising at least two fins substantially perpendicular to the plate and having a constant direction,

- a second part, located at the location of the fluid deflection zone, comprising at least two main deflectors substantially perpendicular to the plate and each having an overall deflection angle,

- A third part comprising the at least two main deflectors and at least two secondary deflectors substantially perpendicular to the plate and interposed between the main deflectors.

The exchanger is also characterized in that the first part is located, according to the direction of circulation of the first fluid, upstream of the second part, itself upstream of the third part.

Thus, this solution achieves the above objective. In particular, the presence of two types of deflectors, main and secondary, makes it possible to perform the deflection of the flow of the first fluid smoothly and combining it with the increase in the density of fins. It thus allows a smooth, progressive transition and significantly reducing pressure drops between:

- the rapid flow of the first fluid in a zone of sparse fins (in the first zone), and

- slower flow of the first fluid within the core of the exchanger with a denser arrangement of fins.

The main and secondary deflectors therefore allow a better distribution of the flow of the first fluid, a reduction in the pressure drop and a better balance of the thermal resistances of the first and second flows located in the heart of the exchanger.

The exchanger also includes one or more of the following features, taken alone or in combination:

• the at least two secondary deflectors are interposed asymmetrically between the at least two main deflectors,
• the at least two main deflectors each have the same overall deflection angle and are separated by a constant spacing,
• the at least two main deflectors each have a different overall angle of deflection and are separated by a variable spacing,
• each main deflector has a rounded portion, the radius of curvature of this portion being between 0.5 cm and 10 cm,
• the second part comprises at least three main deflectors, the spacing between two main deflectors being different from one spacing to another,
• the first fluid circulates on a first face of the plate, the second fluid circulates on a second face of the plate,
• only the first fluid is deflected,
• the first fluid is deflected upstream of the exchange zone and
• downstream of the exchange zone,
• The exchanger is obtained by additive manufacturing.

The invention relates to a turbomachine comprising at least one exchanger having any one of the aforementioned characteristics.

The invention also relates to an aircraft comprising at least one turbomachine as mentioned above.

Brief description of figures

The invention will be better understood, and other aims, details, characteristics and advantages thereof will appear more clearly on reading the detailed explanatory description which follows, of embodiments of the invention given as purely illustrative and non-limiting examples, with reference to the appended schematic drawings in which:

Figure 1 is an example of a core (exchange zone) of a "plate and fin" type heat exchanger for which the present invention is designed,

FIG. 2 is a cross-sectional view of an exchanger comprising a distribution zone according to the invention,

FIG. 3 is a schematic view of a distribution zone of an exchanger according to the invention,

Figure 4 is a schematic view of the opening angle and the overall deflection angle of the deflected fluid flow in the distribution zone.

Figure 5 is a schematic view of a series of "countercurrent" type heat exchangers.

Figure 6 is a schematic view of a "cross-flow" type heat exchanger.

Description of embodiments of the invention

In FIG. 1, a heat exchanger 10 includes an exchange zone 12 in the form of a stack. The heat exchanger 10 can be of the "counter-current" type as illustrated in one of the variants of FIG. 5 or of the "cross-current" type as illustrated in FIG. 6. Thus the zone of exchange 12 comprises at least a first stage E1 and a second stage E2. Each stage E1, E2 is separated from the stage above by a transverse plate 20 sealed. An exchanger 10 conventionally allows an exchange of heat between two fluids 14, 16. Thus, as shown in Figure 1, each stage E1, E2 allows the circulation of a fluid 14, 16: either the first fluid 14, or the second fluid 16. The fluids 14, 16 are thus circulated alternately, so that each stage E1 circulating the first fluid 14 is followed by a second stage E2 circulating the second fluid 16 and vice versa poured. The first fluid 14 thus circulates on a first face of the transverse plate 20 between two stages E1, E2 and the second fluid 16 circulates on a second face of the transverse plate 20 of these two stages E1, E2. In a conventional manner and well known per se, the exchange zone 12 thus makes it possible to transfer thermal energy from one of the fluids 14, 16 to the other fluid 14, 16 without mixing them. There is only the thermal flux which crosses the transverse plate 20 separating the two stages E1, E2. All of the transverse plates 20 of the exchange zone 12 therefore form the exchange surface of the exchanger 10. The exchanger 10 is, moreover, configured so that, in the exchange zone 12 , the first and second fluids 14, 16 circulate in opposite directions, each in their respective stage(s) E1, E2(s). Conventionally, only one of the two fluids 14, 16 is deflected. In the example considered, it is the first fluid 14 of each stage E1 which is deflected.

As already mentioned in the introduction, the direction of flow of the fluids 14, 16 is conventionally imposed by fins 18 extending substantially perpendicular to the transverse plates 20, between two successive plates 20. These fins 18 therefore extend, over the entire length of the path of the fluid 14, 16, in a direction substantially parallel to the direction of flow of the fluids 14, 16.

Upstream of the exchange zone 12 (according to each of the directions of circulation of the fluids 14, 16, the upstream and the downstream changing between a stage E1 and a stage E2), the fins 18 are arranged so as to form conduits 22 independent. Each duct 22 is thus delimited by two fins 18 and two transverse plates 20. Each stage E1, E2 thus comprises at least two fins 18 upstream of the exchange zone 12. In the exchange zone 12, the fins 18 do not are more arranged so as to form ducts 22. Indeed, in this exchange zone 12, the fins 18 are arranged in staggered rows. This staggered arrangement makes it possible to homogenize the temperature in the circulating fluid 14, 16 and therefore to improve heat exchange. Indeed, without this staggered arrangement, the "flow core" of the circulating fluid 14, 16 between each fin 18 would remain hot or cold and would not come into contact with said fins 18. Only the "flow edges" of the fluid circulating 14, 16 would be in contact with the fins 18. The staggered arrangement thus allows the fins 18 to "cut" the flow of fluid 14, 16 circulating and to reach the heart of the flow to cool/heat it in the same way as the edges of the stream.

A difference in density of fins 18 is therefore observed between the exchange zone 12 and the zone upstream of the exchange zone 12. This difference in density of fins 18 which can be, in addition, combined with a deflection (in the case of the first fluid 14) leads to a pressure drop of the fluids 14, 16 but more particularly of the first fluid 14 within the stages E1 of the exchanger 10.

In order to allow the deflection of the first fluid 14, each first stage E1 further comprises, upstream of the exchange zone 12 according to the direction of circulation of the first fluid 14, a distribution zone 24. This distribution zone 24 is illustrated in Figures 2 and 3. The distribution zone 24 comprises, for each conduit 22, a point of deflection of the first fluid 14. All of the deflection points form a deflection zone 26. In the example illustrated in Figures 2 and 3, all of the deflection points 26 are aligned and the deflection zone 26 thus forms a line. This deflection zone 26 makes it possible to define three distinct parts A, B, C of the distribution zone 24. As can be seen in FIGS. 2 and 3, the first part A is located, according to the direction of circulation of the first fluid 14, in upstream of the second part B, itself upstream of the third part C.

The first part A of the distribution zone 24 is located upstream of the deflection zone 26 (in the direction of circulation of the first fluid 14). The fins 18 of part A have a constant direction and form, as already mentioned, the ducts 22. These ducts 22 have a substantially straight line. The walls of the ducts 22 are substantially parallel to each other.

The second part B of the distribution zone 24 is located at the location of the deflection point(s) of the first fluid 14. This second part B comprises at least two main deflectors 28 substantially perpendicular to the transverse plate 20. These main deflectors 28 each have an overall deflection angle β. Each main deflector 28 thus has a portion forming a rounding. The radius of curvature RC (see FIG. 4) of this rounding is between 0.5 cm and 10 cm.

In the embodiment illustrated in FIGS. 2 and 3, certain main deflectors 28 extend in the extension of a corresponding fin 18 and other main deflectors 28 are arranged in the space between two fins 18. The fin 18 and the corresponding main deflector 28 can be made in one piece. Depending on the embodiment considered, the spacings 32 between two successive main deflectors 28 can be identical or not, variable or not. Thus, in the embodiment illustrated in Figures 2 and 3, the main deflectors 28 each having the same overall deflection angle β, are all separated by a constant spacing 32 (also visible in Figure 4). In an embodiment not shown, the main deflectors 28 each have a different overall deflection angle β and are separated by a variable spacing 32. According to another embodiment not shown, the second part B comprises the main deflectors 28 each having the same overall deflection angle β but the spacing 32 between two successive main deflectors 28 is different from one spacing 32 to another.

The overall deflection angle β of the second part B of the distribution zone 24 is defined between the direction of the fins 18 of the first part A of the distribution zone 24 and the direction of the fins 18 of the exchange zone 12 The order of magnitude of the angle β is between 90° and 120°. Advantageously, the angle of magnitude of the angle β is between 90 and 105° and is preferably equal to 90°.

The overall deflection angle β is conventionally complementary to an opening angle α. This opening angle α defines the inclination of the fins 18 of the first part A of the distribution zone with respect to a straight line perpendicular to the direction of the fins 18 of the exchange zone 12. The opening angle α is thus defined as α = (β – 90 ) and is between 0° and 30°. This is illustrated in Figure 4.

The third part C comprises the main deflectors 28 of part B and also at least two secondary deflectors 30. These secondary deflectors 30 are also substantially perpendicular to the transverse plate 20. They are inserted between the main deflectors 28, as visible on FIGS. 2 and 3. Depending on the embodiment considered, the spacings between the main deflectors 28 and the secondary deflectors 30 can be identical or not, variable or not. Thus, in the embodiment illustrated in Figures 2 and 3, the secondary deflectors 30 are inserted symmetrically between the main deflectors 28. But these secondary deflectors 30 can also be inserted asymmetrically between the main deflectors 28. For example on Figure 4, we see that the secondary deflectors 30 are inserted asymmetrically between the main deflectors 28.

We therefore clearly observe, downstream of the inflection zone 26 of the distribution zone 24, a progressive densification of the elements (fins 18 and deflectors 28, 30) arranged on the passage of the fluid 14 and a progressive disappearance of the ducts 22. In the embodiment illustrated in FIG. 3, it can also be seen that the first fluid 14 of each stage E1 is deflected a first time upstream of the exchange zone 12 and a second time downstream of the exchange zone 12 Upstream of the exchange zone 12, the two types of successive deflectors 28, 30 make it possible to gradually densify the number of elements (fins 18 and deflectors 28, 30) arranged on the passage of the fluid, thus increasing the number of surfaces inversely proportional to the deceleration of the fluid 14 due to the pressure drop of the fluid 14 induced by the deflection imposed in part B of the distribution zone 24. This makes it possible to maintain an exchange coefficient sufficiently important to maintain a good balance between the thermal resistances associated with each of the two flows 14, 16. This progressive densification of the elements 18, 28, 30 also makes it possible to maintain a good distribution of the flow of the fluid 14 and to limit the turbulences and recirculation zones despite the head loss associated with deflection.

Downstream of the exchange zone 12, these two types of deflectors 28, 30 make it possible to gradually reduce the number of elements 18, 28, 30 in the direction transverse to the flow with the acceleration of the flow induced by the output of the exchange zone 12 (see above).

The reduction of the recirculation zones of the first fluid 14 and of the maldistribution also makes it possible to obtain (in addition to the reduction in pressure drops and the increase in heat exchanges) a more homogeneous temperature which makes it possible to reduce the thermomechanical stresses . A recirculation zone is a zone in which part of the flow in circulation forms a vortex on itself and therefore no longer circulates. A non-homogeneous distribution of velocity is called maldistribution.

The solution proposed by the present invention is particularly suitable for heat exchangers 10 produced by additive manufacturing by selective melting on powder beds. This additive manufacturing solution presents much less difficulty in production than traditional brazing manufacturing processes. Moreover, additive manufacturing processes do not necessarily require specific supports during manufacturing.

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Claims (12)

Heat exchanger (10) for a turbomachine, comprising at least a first and a second stage (E1, E2) separated by a transverse plate (20), each stage (E1, E2) allowing the circulation respectively of a first fluid (14) and a second fluid (16), the exchanger (10) being configured so that the first and the second fluid (14, 16) each circulate in its stage (E1, E2) and intersect in an exchange zone (12), at least one of the first and second stages (E1, E2) further comprising, upstream of the exchange zone (12) in the direction of circulation of the first fluid ( 14), a distribution zone (24), the distribution zone (24) comprising a deflection zone (27) of the first fluid (14),
the exchanger (10) being characterized in that:
- the distribution zone (24) has three distinct parts (A, B, C):
- a first part (A), located upstream of the deflection point, comprising at least two fins substantially perpendicular to the plate (20) and having a constant direction,
- a second part (B), located at the location of the deflection zone (27) of the fluids (14, 16), comprising at least two main deflectors (28) substantially perpendicular to the plate (20) and each having a global deflection angle (β),
- a third part (C) comprising the at least two main deflectors (28) and at least two secondary deflectors (30) substantially perpendicular to the plate (20) and interposed between the main deflectors (28), and
- the first part (A) is located, according to the direction of circulation of the first fluid (14), upstream of the second part (B), itself upstream of the third part (C). Exchanger (10) according to the preceding claim, characterized in that the at least two secondary deflectors (30) are inserted asymmetrically between the at least two main deflectors (28). Exchanger (10) according to any one of the preceding claims, characterized in that the at least two main deflectors (28) each have the same overall deflection angle (β) and are separated by a constant spacing (32a). Exchanger (10) according to any one of claims 1 or 2, characterized in that the at least two main deflectors (28) each have a different overall deflection angle (β) and are separated by a variable spacing (32). Exchanger (10) according to one of Claims 3 and 4, characterized in that each main deflector (28) has a rounded portion, the radius of curvature of this portion being between 0.5 cm and 10 cm. Exchanger (10) according to any one of the preceding claims, characterized in that the second part (B) comprises at least three main deflectors (28), the spacing (32) between two main deflectors (28) being different from one spacing to another. Exchanger (10) according to any one of the preceding characteristics, characterized in that the first fluid (14) circulates on a first face of the plate (20), the second fluid (16) circulates on a second face of the plate ( 20). Exchanger (10) according to any one of the preceding characteristics, characterized in that only the first fluid (14) is deflected. Exchanger (10) according to any one of the preceding characteristics, characterized in that the first fluid (14) is deflected upstream of the exchange zone (12) and downstream of the exchange zone (12). Exchanger (10) according to any one of the preceding claims, characterized in that it is obtained by additive manufacturing. Turbomachine comprising at least one exchanger (10) according to any one of the preceding claims. Aircraft comprising at least one turbomachine according to the preceding claim.