WO2018060645A1

WO2018060645A1 - Heat exchanger comprising a phase change material

Info

Publication number: WO2018060645A1
Application number: PCT/FR2017/052660
Authority: WO
Inventors: Kamel Azzouz; Julien Tissot; Xavier Marchadier; Michael LISSNER; Patrick Boisselle; Samuel BRY; Ambroise SERVANTIE
Original assignee: Valeo Systemes Thermiques
Priority date: 2016-09-28
Filing date: 2017-09-28
Publication date: 2018-04-05

Abstract

The heat exchanger comprises: an inlet collector box, an outlet collector box, and heat exchange channels connecting the two collector boxes. The channels and the collector boxes form a circuit through which an internal heat-transfer fluid flows. According to the invention, at least one casing, known as a phase change casing, having a generally tubular shape encapsulating a phase change material is housed inside at least one heat exchange channel.

Description

Heat exchanger comprising a phase change material

The present invention relates to the field of heat exchangers and more particularly that of heat exchangers on board a motor vehicle, in particular engine coolant cooling radiators or charge air coolers.

Motor vehicles are subject to a highly variable environment during taxiing. Indeed, the normal operation of the vehicle creates significant variations in the temperature of different bodies such as the engine block, (especially during rises and descents of speed that occur at acceleration and deceleration of the vehicle). In addition, the vehicle can move from cold air zones to hot air zones, and vice versa, and be exposed to various weather conditions (rainwater for example) that can further accentuate organ temperature variations.

In order to make it possible to mitigate the temperature variations of these members, motor vehicles are equipped with temperature control circuits comprising one or more heat exchangers. Usually, heat exchangers for motor vehicles comprise heat exchange channels in which circulates a heat transfer fluid. During its circulation in the heat exchange channels, the coolant exchanges heat with the medium surrounding the heat exchange channels. These heat exchanges are intended to heat or cool the heat transfer fluid. Two collector boxes respectively inlet and outlet are arranged on either side of the heat exchange channels so as to form a coolant circulation circuit extending from an inlet of the collector box of input to an outlet port of the outlet manifold box. The heat transfer fluid circulates in this circuit through the different heat exchange channels.

This type of heat exchanger is sized to withstand the temperatures reached during normal operation of the vehicle and dissipate enough heat in the temperature ranges defined by the car manufacturers. The most extreme temperatures are reached only briefly during certain operating stages of the exchanger. These short periods during which These extreme temperatures are known as temperature peaks.

These heat exchangers are traversed by a coolant whose temperature varies over time depending on the temperature of the organs to be cooled. The temperature of the coolant undergoes relatively high frequency variations around an average value corresponding to a given operating regime of the organs to be cooled. This can be explained in particular by the fact that the engine speed of the vehicle varies very often when driving, especially in urban areas, traffic jams, uphill climbs, descents, etc. The temperature of the fluid leaving the engine to be cooled, and therefore at the inlet of the heat exchanger, thus varies frequently.

Peak temperatures can be difficult to dissipate through the exchanger. As a result, it may happen that the engine components to be cooled temporarily rise to operating temperatures beyond the recommended range for optimum engine operation. For example, the recommended range for good carburettor conditions of the engine is between 80 and 100Ό.

The object of the invention is to remedy these drawbacks by providing a heat exchanger making it possible to reduce the variations of the temperature of the heat transfer fluid passing through it during the rolling and consequently to better control the thermal regulation of the various members.

For this purpose, the invention relates to a heat exchanger comprising:

- an input manifold box,

an outlet manifold, and

heat exchange channels connecting the two collector boxes, the channels and collector boxes forming a circuit for circulating an internal heat-transfer fluid, in which at least one so-called phase-change envelope of generally tubular shape encapsulating a material for phase change is accommodated in at least one heat exchange channel.

Thus, the envelope encapsulating the phase change material effectively absorbs excess heat caused by more or less significant temperature peaks at the input of the heat exchanger, specifically in the heat exchange channel. The phase change material allows this absorption of heat via a change of state of the material according to the temperature of the fluid coolant, in this case by liquefaction of the phase change material when the heat transfer fluid reaches a temperature greater than or equal to the melting temperature of the phase change material. The variation of the temperature of the coolant at the outlet of the heat exchanger is thus attenuated. The temperature of the fluid at the outlet of the exchanger is therefore more stable. The cooling of the bodies receiving the coolant is then more efficient and the temperature of the latter varies less brutally.

It is thus understood that the impact of the temperature peaks is reduced or canceled by smoothing the rise in temperatures obtained via the presence of the phase change material within at least one heat exchange channel of the exchanger. This smoothing in the temperature regulation of the heat transfer fluid makes it possible to better maintain the engine under optimal operating conditions. Moreover, thanks to the heat exchanges that a channel with its environment, in particular the air passing through the heat exchanger, has, the envelope comprising the phase change material placed inside a heat exchange channel makes it possible to regenerate the phase change material (by recrystallization or solidification of the phase change material). Indeed, when the temperature of the heat transfer fluid returns within a prescribed range (typically between 80 and 90Ό), the phase change material will gradually release the stored heat and change state, by crystallization. Thus regenerated, recrystallized phase change material can absorb a next peak temperature.

As a purely illustrative example, when the vehicle is in a climb, the bodies to be cooled are highly stressed which can cause a temperature spike of the coolant at the inlet of the exchanger. The change material located in the envelope housed in the heat exchange channel will then change state, ie liquefy, and thus absorb at least in part this sudden rise in temperature. Then, when the vehicle is in a descent, the bodies to be cooled are then less stressed. The heat transfer fluid entering the exchanger will return to the temperature range prescribed for the optimal operation of the engine, and the phase change material will retransmettre heat transfer fluid heat stored during the heat peak rise. By releasing this heat, the phase change material will then regenerate by recrystallizing. During the first tests, it turns out that the maximum temperature measured at the outlet of the exchanger has been reduced by 3 ° compared to a conventional heat exchanger. According to other optional features corresponding to different embodiments of the heat exchanger:

the phase change material has a latent heat of fusion greater than 280 kJ / m 3;

the phase-change material passes from the solid phase to the liquid phase in a melting point range of between 20 and 110 °, and more particularly chosen:

• between 45 and 55Ό if the heat exchanger is intended for the cooling of the engine charge air,

• between 50 and 100Ό if the heat exchanger is designed for the cooling of a gearbox,

• between 80 and 110Ό if the heat exchanger is for engine cooling;

the phase-change material is chosen from a fatty acid, a fatty alcohol of vegetable origin, a paraffin and a hydrated salt;

the internal heat transfer fluid is in liquid form;

the casing has a circular section whose maximum outside diameter is between 1 mm and 8 mm;

- the envelope has an oval section;

- the envelope has a rectangular section

the envelope has a transverse section comprising two opposite longitudinal faces, the longitudinal faces being:

• each convex,

• respectively provided with at least two concave portions separated by a convex portion;

the envelope has a section whose length corresponds to more than 80% of the length of the envelope, this section having a circular section whose diameter is between 1 and 4 mm, and more particularly chosen from 4 mm, 2 , 56 mm, 1, 4 mm, 1, 7 mm, 1, 88 mm and 1, 1 mm;

the envelope has a thickness of between 50 and 500 μm, preferably equal to 200 μm;

the exchanger comprises means for positioning the envelope in the channel heat exchange;

the heat exchange channel containing the envelope has a section chosen from a section of generally round, oval, and oblong shape;

the exchanger being of the mechanical type or of the brazed type;

the heat exchange channels are divided into first and second groups of channels, each heat exchange channel of the first group comprising a phase change envelope, and each heat exchange channel of the second group not including any phase change envelope;

the first and second groups of heat exchange channels are respectively placed in first and second opposite parts of the heat exchanger, the first part delimiting, for example, a first heat exchange face of the heat exchanger and the second portion delimiting a heat exchanger; second heat exchange face of the exchanger without delimiting the first heat exchange face, or each of the first and second portions delimiting both the first and second heat exchange faces;

the heat exchange channels being arranged on at least one line, the heat exchange channels of the first group alternate on this line with the heat exchange channels of the second group.

The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the appended drawings, in which:

- Figure 1 is a perspective view of a portion of a heat exchanger according to a first embodiment of the invention, a cutaway being shown on a manifold of this heat exchanger, the heat exchanger forming radiator;

FIG. 2 is a perspective view of a phase change envelope with a longitudinal section of a central portion of this envelope;

FIG. 3 is a section of a heat exchange channel duct of the exchanger of FIG. 1;

FIGS. 4 to 6 are illustrations of other examples of possible heat exchange channel sections in which a phase change envelope is housed; and

FIG. 7 is a graph showing the evolution as a function of time (abscissa) of the temperature of the air leaving the radiator heat exchanger (left-hand ordinate) and the speed of a vehicle equipped with this radiator (right ordinate).

FIG. 8 is a view from above of a heat exchanger according to another embodiment embodiment of the invention comprising heat exchange channel conduits incorporating phase change envelopes and phase change envelope free channels;

FIG. 9 is a perspective view of a portion of a heat exchanger according to another embodiment of the invention comprising heat exchange channel ducts incorporating phase change envelopes and ducts without envelopes to phase change; _et

FIG. 10 is a perspective view of a heat exchanger according to another embodiment of the invention comprising heat exchange channel conduits incorporating phase change envelopes and phase change envelopes without channels.

FIG. 1 represents a heat exchanger 2 according to a first embodiment of the invention, here a radiator. It may be in this case a radiator for cooling a coolant of an engine. Such an exchanger may be of mechanical type, that is to say which comprises elements assembled together by crimping, or brazed type, that is to say which comprises elements assembled together by brazing. This exchanger comprises a plurality of conduits forming heat exchange channels 4 parallel to each other. These ducts may have a section 6 (see FIG. 3) of generally oblong shape, for example. They are substantially identical to each other. With particular reference to Figure 3, it will be noted that the length (large dimension) of the section of the channels 4 may vary from one exchanger to another; it may for example be 12.98 mm or 10.16 mm. It is the same for the average width (small dimension) of the section which can for example be equal to 1, 7 mm (when the length is equal to 12.98 mm) or to 1.79 mm (when the length is equal to 10.16 mm). The central width 8 of the heat exchange channel 4 may be smaller than the width 10 at the ends. The ducts 4 then have two heat exchange faces which are the upper 14 and lower faces 15 in FIG. 3. Each end of the ducts 4 is fixed to a collector plate 16 (which may also be called a "collector") positioning the ducts. 4 between them. An inlet or outlet manifold 18 is attached to the header plate16. Another manifold (not shown), substantially identical to the manifold 18, is located at the other end of the exchanger, that is to say at the other end of the heat exchange channels, and is attached to another manifold plate (not shown) substantially identical to the manifold plate 16. Thus, the ducts 4 connect the two boxes collectors between them.

During the operation of the heat exchanger 2, an internal heat transfer fluid enters through an inlet orifice formed in the inlet manifold, circulates inside the heat exchange channels 4 to the outlet manifold and leaves the heat exchanger 2 through an outlet orifice formed in the outlet manifold. This fluid is generally a coolant (for example brine) in the case of a radiator but can also be air in the context of a heat exchanger type charge air cooler. During its circulation inside the heat exchange channels 4, the internal heat transfer fluid transmits heat to the walls of these heat exchange channels 4. The heat exchanger 2 is traversed by an external heat transfer fluid, which is air circulating between the ducts forming the heat exchange channel 4. The heat exchanger 2 transmits the heat received by the internal heat transfer fluid to the external heat transfer fluid. This transmission is effected by means of cooling fins (not shown) extending in particular between the heat exchange channels 4.

Thus, the temperature of the internal heat transfer fluid at the outlet of the heat exchanger 2 is lower than the temperature of this same fluid at the inlet of the heat exchanger.

As illustrated in FIG. 2, envelopes 19, called phase-change envelopes, have a generally tubular shape and encapsulate a phase-change material 20. These envelopes 19 are housed inside the channels forming heat-exchange channels 4 .

A phase change material is a material whose latent heat is important and which is used in a temperature range including its phase change temperature. In this way, a phase change material is capable of absorbing or returning a large amount of heat during its phase change. The phase change material may be a fatty acid, a fatty alcohol of plant origin, a paraffin or a hydrated salt. It has a latent heat of fusion greater than 280 kJ / m3 which allows it to store a large amount of energy. The melting temperature of the phase-change material is in a temperature range between 20 and 110 °, and which may more particularly be chosen between 50 and 100 ° (for a low-temperature exchanger intended for cooling a gearbox vehicle for example) chosen from 45Ό to 55Ό (for a low temperature heat exchanger for typically cooling the engine charge air) and 80Ό to 110Ό (for a high temperature heat exchanger for cooling the engine). In the illustrated example (see in particular Figure 3), the envelopes 19 have a circular section whose maximum outside diameter 22 is between 1 mm and 8 mm. More particularly, the envelopes 19 have a section whose length corresponds to more than 80% of the length of each envelope 19 having a circular section whose diameter is between 1 and 4 mm, and may in particular be chosen from 4 mm, 2 , 56 mm, 1, 4 mm, 1, 7 mm, 1, 88 mm and 1, 1 mm. The choice of this diameter is made according to the size and shape of the section of the heat exchange channel duct 4. For example, the diameter of the section of the section of the envelopes 19 is 1.7 mm for a 12.98 mm long conduit and 1.7 mm average width or 1.88 mm for a conduit with a length of 10.16 mm and an average width of 1.79 mm. The diameter of the section of the envelopes 19 partly determines the heat exchange surface between the internal heat transfer fluid and the phase change material. The diameter as well as the length of the envelopes 19 contribute to determining the efficiency of the heat exchange between each phase change envelope 19 and the internal heat transfer fluid. Other forms of channels 4 and envelopes 19 will be described later.

The wall of the main body of the envelope has a thickness of between 50 μηη and 500 μηι, preferably equal to 200 μηι. The phase change envelopes 19 illustrated in FIG. 2 may be made of synthetic material, more particularly of plastic material. The main body 24 of the envelopes is hollow in order to accommodate the phase-change material 20. Each end of an envelope 19 is closed by a plug 26 comprising an inner end (not shown in the figures) nested in the end of the casing 19 and an outer end 27 provided with an axial orifice 27A for fixing the casing in the heat exchanger 2 (see Figures 1 and 2).

Reference will now be made to FIGS. 4 to 6, in which various section shapes of conduits forming heat exchange channels are illustrated. In the example of FIG. 4, the ducts forming heat exchange ducts 4 have a circular section with a diameter 28, which may be equal to 8.35 mm, for example. Here, a single envelope 19 is present by conduit 4. This envelope can for example be of a diameter 30 equal to 4 mm. It is also possible that the channels forming heat exchange channels have a section of generally oblong shape and comprising three enlarged portions (see Figure 5). The length of the section can then be 12.06 mm and its average width is 1.69 mm. The section of the phase change envelope is then 1.1 mm. This section may also be oval shaped, as shown in Figure 6, and have a length of 12.40 mm and a maximum width of 4.82 mm or a length of 12.96 mm and a width of 3.19. mm for example. The section of the phase change envelope can then be 2.56 mm and 1.4 mm, respectively.

The phase change envelopes 19 make it possible to stabilize the temperature of the internal heat transfer fluid at the outlet of the heat exchanger 2, as illustrated in FIG. 7. The curve A represents the evolution of the temperature of the air coming out of a radiator comprising the phase change envelopes 19. The curve B represents this same evolution, and this in the case where the radiator does not include phase change envelopes 19. There is a very strong attenuation of all the peaks temperatures on the curve A with respect to the curve B and this regardless of the speed of the vehicle (and therefore the engine speed). The speed is represented by the curve C. During the passage of the internal heat transfer fluid in the heat exchange channel 4, it comes into contact with the phase change envelope 19. If the temperature of the internal heat transfer fluid is greater than or equal to at a temperature within the phase change range of the phase change material 20, the phase change material (e.g. solid phase to liquid phase) and absorb excess heat caused by higher or lower temperature peaks. This absorption allows the stabilization of the temperature of the internal heat transfer fluid at the outlet of the heat exchanger 2.

The envelopes 19 may, in the first embodiment illustrated in Figures 1, 3, 5 and 6, the number of two per duct 4 and located opposite one another considering the large size of the channel d heat exchange 4. They are housed parallel to each other and parallel to a main axis X of the channel (see Figure 1).

The phase change envelopes 19 are held in position inside the heat exchange channels by positioning means. These positioning means ensure, on the one hand, an axial positioning of the phase change envelopes 19 in the heat exchange channels 4 and, on the other hand, a radial positioning to maintain the envelopes in a position such that the internal heat transfer fluid circulates at least along a portion of the envelope, and preferably all around the envelopes 19 to increase the contact area between the latter and the phase change envelopes 19 and thus increase the efficiency of the heat exchange.

In what follows, other embodiments of the invention will be described with reference to FIGS. 8 to 10. In these figures, the elements similar to those of the preceding figures are designated by references comprising numbers of the units and dozens identical.

In one embodiment of the invention shown in FIG. 8, the heat exchange channels are divided into first and second groups of channels 348 and 350, each heat exchange channel 304 of the first group 348 comprising an envelope with phase change 319, and each heat exchange channel 305 of the second group 350 does not comprise a phase change envelope. The channels of the second group have a section of oblong general shape. The channels 304 have a circular section. More specifically, the first and second groups 348 and 350 of heat exchange channels 304 are respectively placed in first and second opposite parts of the exchanger. The first part delimits, for example, a first heat exchange face F1 of the heat exchanger 302 and the second portion delimits a second heat exchange face F2 of the heat exchanger 302 without delimiting the first heat exchange face F1. More specifically, the channels 304 of the first group 348 are arranged on a line substantially parallel to a second line composed of the channels 305 of the second group 350. The faces F1 and F2 are substantially parallel and opposite.

By adjusting the total number of conduits 304 and 305 respectively with and without phase change envelope 319, it is possible to produce a circulation of the internal heat transfer fluid in the form of "I" or in the form of "U" of the internal heat transfer fluid .

An "I" circulation corresponds to a circulation of the internal heat transfer fluid from an inlet manifold towards an outlet manifold through straight ducts. A "U" circulation may correspond to:

- A circulation of the internal coolant in a heat exchanger comprising only one common manifold. (the collector box The common part can then be divided into two parts for example, one part acting as an input collector box and the other part serving as an output collector box, the two parts then being interconnected by a set of exchange channels. thermals in the form of "U" imposing U-shaped paths to the internal heat transfer fluid);

a circulation of the heat transfer fluid, via certain heat exchange channels of the heat exchanger, in a first direction between the two collecting boxes and, a circulation in a second direction, opposed to the first direction, via other channels. In a "U" circulation embodiment, the common manifold box can be divided into two parts, one part acting as an inlet manifold box and the other part acting as an outlet manifold box. The two parts are connected together by a set of heat exchange channels in the shape of "U" imposing U-shaped paths to the internal heat transfer fluid.

According to another "U" circulation embodiment, a first manifold is configured to have an inlet manifold portion and another outlet manifold portion (both collector box portions may be separated by a partition for example). The second collector box is itself configured to be connected with all the heat exchange channels. The two parts of the first water box are thus connected to each other by:

a first set of heat exchange channels in which the fluid flows towards the second collecting box,

- the second collector box,

- A second set of heat exchange channels in which the fluid having passed through the second collector box, flows to the first collector box.

In the embodiment of the invention illustrated in FIG. 9, each of the groups of channels 448 and 450 of the first and second opposite parts of the exchanger 402 delimit both the first and second heat exchange faces F1, F2. .

It is possible to vary the ratio between the channels of the first and second groups. Since the passage section is higher for the ducts 404 containing the phase change envelopes 419 than the ducts 405 without phase change envelopes, this heat exchanger configuration 402 is recommended for an "I" circulation of the heat transfer fluid. internal. In another embodiment of the invention illustrated in FIG. 10, the heat exchange channel ducts of the exchanger 502 are arranged on at least one line 556, the heat exchange channels 504 comprising the change envelopes. phase 519 of the first alternating group on this line with the heat exchange channels 505 of the second group. This embodiment is suitable for circulation in "I" and "U".

Regarding the aforementioned embodiments, the outer diameter of the envelopes is adjusted relative to the dimensions of the ducts without casing to meet the iso-thickness condition of the water blade.

The invention is not limited to the embodiments presented and other embodiments will become apparent to those skilled in the art. In particular, it is possible for the envelope to be of oval, rectangular cross-section, or with two convex longitudinal flanks, or two longitudinal flanks respectively provided with at least two concave portions separated by a convex portion.

In addition, the heat exchanger on which the aforementioned examples are based is a radiator for cooling an engine. However, the invention can be applied to any type of low and high temperature exchanger such as charge air coolers or other.

Claims

Heat exchanger (2) comprising:

an inlet manifold box (18),

an outlet manifold (18), and

heat exchange channels (4) connecting the two collector boxes (18),

the channels (4) and collecting boxes (18) forming a circulation circuit for an internal heat transfer fluid,

characterized in that at least one casing (19), called phase change, of generally tubular shape encapsulating a phase change material (20) is housed in at least one heat exchange channel (4).

The heat exchanger of claim 1, wherein the phase change material (20) has a latent heat of fusion greater than 280 kJ / m3.

A heat exchanger according to any one of the preceding claims, wherein the phase change material (20) is passed from the solid phase to the liquid phase in a temperature range of from 20 to 0.

A heat exchanger according to claim 3, wherein, for cooling a vehicle gearbox, the temperature range at which the phase change material (20) passes from the solid phase to the liquid phase is selected from 50 and ^ 00.

A heat exchanger according to claim 3, wherein, for cooling a box of charge air of an engine, the temperature range at which the phase change material (20) passes from the solid phase to the liquid phase is chosen between 45 and δδ.

A heat exchanger according to claim 3, wherein, for cooling a vehicle engine, the temperature range at which the phase change material (20) passes from the solid phase to the liquid phase is selected from 80 to 110 .

7. Heat exchanger according to any one of the preceding claims, wherein the phase change material (20) is selected from a fatty acid, a vegetable fatty alcohol, a paraffin and a hydrated salt.

8. Heat exchanger according to any one of the preceding claims, wherein the internal heat transfer fluid is in liquid form.

9. Heat exchanger according to any one of the preceding claims, wherein the casing (19) has a circular section whose maximum outside diameter (22) is between 1 mm and 8 mm.

10. Heat exchanger according to the preceding claim, wherein the casing (19) has a section whose length corresponds to more than 80% of the length of the casing, this section having a circular section whose diameter is between 1 and 4 mm, and preferably selected from 4 mm, 2.56 mm, 1, 4 mm, 1, 7 mm, 1, 88 mm and 1, 1 mm.

11. Heat exchanger according to any one of claims 1 to 8, wherein the casing (19) has an oval section. 12. Heat exchanger according to any one of claims 1 to 8, wherein the casing (19) has a rectangular section.

13. Heat exchanger according to any one of claims 1 to 8, wherein the casing (19) has a cross section having two opposite longitudinal faces, the longitudinal faces being each convex,

14. Heat exchanger according to any one of claims 1 to 8, wherein the casing (19) has a cross section having two opposite longitudinal faces, the longitudinal faces being respectively provided with at least two concave portions separated by a portion. convex.

15. Heat exchanger according to any one of the preceding claims, wherein the casing (19) has a thickness between 50 and 500 μιη, preferably equal to 200 μηι.

16. Heat exchanger according to any one of the preceding claims, wherein the heat exchange channel (4) containing the envelope has a section selected from a section of generally round, oval, and oblong shape.

Heat exchanger according to any one of the preceding claims, the exchanger being of the mechanical type or brazed type.

18. A heat exchanger according to any one of the preceding claims (302; 402; 502), wherein the heat exchange channels (304; 404; 504) are divided into first and second groups of channels; heat exchange (304; 404; 504) of the first group comprising a phase change envelope (319; 419; 519), and each heat exchange channel (305; 405; 505) of the second group not comprising an envelope phase change.

The heat exchanger (302; 402) of claim 20, wherein the first and second groups of heat exchange channels (304; 404) are respectively located in first and second opposed portions of the heat exchanger,

the first part delimiting, for example, a first heat exchange face (F1) of the exchanger and the second portion delimiting a second heat exchange face (F2) of the heat exchanger without delimiting the first heat exchange face,

or each of the first and second portions delimiting both the first and second heat exchange faces (F1, F2).

22. Heat exchanger (502) according to claim 22, wherein, the heat exchange channels being arranged on at least one line, the heat exchange channels of the first group alternate on this line with the heat exchange channels of the second group.