FR3061745A1 - THERMAL DIFFUSION DEVICE - Google Patents

Abstract

The invention relates to a thermal diffusion device with heat pipe effect comprising a coolant (1) and a housing (2), the housing (2) having a bottom wall (21) forming a bottom, an upper wall (22) opposite the lower wall (21) and four side walls between the lower (21) and upper (22) walls, the side walls consisting of: - two transverse side walls, - two longitudinal side walls, a first longitudinal side wall being intended to receive a hot source, characterized in that: - the distance between the longitudinal side walls is between 1/2 and 2 times the capillary length of the coolant (1), - the quantity (Qf) of coolant (1) contained in the device is between 25 and 80% of the total volume (Vtot) of the housing (2).

Description

(® Agent (s): LTL SAS.

FR 3,061,745 - A1 (54) THERMAL DIFFUSION DEVICE.

(© The invention relates to a heat diffusion device with heat pipe effect comprising a heat transfer fluid (1) and a housing (2), the housing (2) having a bottom wall (21) forming the bottom, an upper wall (22) opposite at the bottom wall (21) and four side walls between the bottom (21) and top (22) walls, the side walls consisting of:

- two transverse side walls,

- two longitudinal side walls, a first longitudinal side wall being intended to receive a hot source, characterized in that:

- the distance between the longitudinal side walls is between 1/2 and 2 times the capillary length of the heat transfer fluid (1),

- The quantity (Q _f ) of heat transfer fluid (1) contained in the device is between 25 and 80% of the total volume (V _tot ) of the housing (2).

THERMAL DIFFUSION DEVICE

FIELD OF THE INVENTION

The present invention relates to the general technical field of heat exchangers, in particular for the removal of heat from an element to be cooled, such as an electronic component.

More specifically, the present invention relates to the technical field of two-phase heat diffusers of the heat pipe type. Such thermal diffusers can be used for many applications such as applications in aeronautics, railways, aerospace, power electronics, etc.

PRESENTATION OF THE PRIOR ART

The components of electronic cards dissipate a significant amount of heat, causing a significant increase in their temperature and associated electronic circuits.

However, an excessive increase in the temperature of these electronic components can cause a drop in their reliability and / or reduce their lifespan. This is why it is necessary to efficiently dissipate the heat dissipated by the electronic components.

Heat exchangers are systems that take heat from one environment and redistribute it to another. There are different categories of heat exchangers for transporting heat from a hot source (for example, an electronic component) to a cold source (for example, a water condenser). When the surface of the cold source is significantly larger than the surface of the hot source, the heat transfer includes a heat diffusion component, and the heat exchanger is called a "thermal diffuser".

We know in particular:

- the flat solid diffuser which generally consists of a block of material with high thermal conductivity such as a metal; such a diffuser operates by simple conduction of heat in the block of material,

the capillary heat pipe which generally consists of a housing containing a liquid and a capillary structure in thermal contact with the internal walls of the housing, the liquid being located mainly in the capillary structure and flowing from the cold source to the hot source, the steam produced at the hot source occupying the entire steam space and condensing at the cold source,

- the two-phase thermosyphon which consists of a housing including a two-phase fluid circulating under the effect of gravitational forces, gravity being the motor for the return of the condensed liquid in the evaporation zone.

Each type of existing thermal diffuser has advantages and disadvantages. This is why the choice of a type of thermal diffuser depends on the intended application, and more precisely on the constraints associated with this application.

In certain applications, such as applications for cooling power electronics in the aeronautical field, it is necessary for the heat exchanger to meet the following constraints:

- good efficiency at high flux density (ie flux density greater than a few W / cm ² ), that is to say low thermal resistance,

- low constraints on the positioning of hot springs,

- low tilt sensitivity (limited thermal performance degradation for tilt changes of ± 40 °),

- good homogenization of temperatures,

- low complication in case of frost,

- low weight,

- simplicity and low cost.

However, none of the above-mentioned thermal diffusers can meet all of these constraints.

Indeed :

- the flat massive diffuser is heavy and ineffective at high flux density,

- the capillary heat pipe is complex, expensive, and sensitive to freezing (the capillary structure being able to deteriorate when the liquid which it contains solidifies), and its thermal performances degrade at high densities of flow,

- the two-phase thermosiphon - by the use of gravitational forces for the circulation of the fluid - is sensitive to inclinations and very strongly constrained with regard to the positioning of hot and cold sources.

An object of the present invention is to propose a thermal diffuser making it possible to meet the above-mentioned constraints, and more precisely a thermal diffuser:

- having good efficiency at high flux density (ie flux density greater than a few W / cm ² ),

- in which the hot springs can be positioned in different zones,

- not very sensitive to inclination,

- not at risk of being damaged in the event of frost,

- with low weight,

- simple and inexpensive.

SUMMARY OF THE INVENTION

To this end, the invention provides a heat diffusion device with a heat pipe effect comprising a heat transfer fluid and a housing, the housing comprising a bottom wall forming a bottom, an upper wall opposite the bottom wall and four side walls between the bottom walls and upper, the side walls consisting of:

- two transverse side walls,

- two longitudinal side walls, a first longitudinal side wall being intended to receive a hot source, remarkable in that:

- the distance between the longitudinal side walls is between% and 2 times the capillary length of the heat transfer fluid,

- The quantity of heat transfer fluid contained in the device is between 25 and 80% of the total volume of the housing.

Preferred but non-limiting aspects of the device according to the invention are as follows:

- The device can be devoid of capillary structure;

- The hot source can be intended to be positioned in an evaporation zone of the first longitudinal side wall, the area of the evaporation zone being less than 40% of the total area of the first longitudinal side wall;

- the position of the evaporation zone on the first longitudinal side wall can be such that:

• the distance between the evaporation zone and each transverse side wall is greater than or equal to one fifth of the length of the first longitudinal side wall, • the distance between the evaporation zone and the upper wall is greater than or equal to one third of the height of the first longitudinal side wall, and • the distance between the evaporation zone and the bottom wall is zero;

- The external face of the first longitudinal side wall may include a positioning mark to define the position of the evaporation zone;

- The device may include spacers between the internal faces of the longitudinal side walls of the housing, each spacer being intended to cooperate with respective fixing means;

- The internal faces of the longitudinal side walls may include a surface texturing;

- the surface texturing can consist of grooves formed on the internal faces of the longitudinal side walls, the grooves extending between the lower and upper walls of the housing;

- the heat transfer fluid may be water.

BRIEF DESCRIPTION OF THE FIGURES

Other advantages and characteristics of the thermal diffusion device will emerge more clearly from the description which follows of several variant embodiments, given by way of nonlimiting examples, from the appended drawings in which:

- Figures 1 and 2 illustrate an embodiment of a thermal diffuser according to the invention,

- Figures 3 and 5 are side views illustrating the operating principle of the thermal diffuser

- Figures 4 and 6 are front views illustrating the operating principle of the thermal diffuser.

DETAILED DESCRIPTION

We will now describe in more detail the device according to the invention with reference to the figures. In these various figures, the equivalent elements are designated by the same reference numeral.

Referring to Figure 1, an embodiment of a thermal diffusion device has been illustrated.

The device comprises a heat transfer fluid 1 and a housing 2 for containing the heat transfer fluid 1.

1. Thermal diffusion device

1.1. Coolant

The heat transfer fluid 1 makes it possible to transport the heat produced by the element to be cooled (not shown).

The heat transfer fluid 1 is contained in the housing 2, the interior volume of which constitutes a sealed enclosure for the heat transfer fluid. The vacuum is created in the housing 2 prior to the introduction of the heat transfer fluid 1. The heat transfer fluid is then in a state of liquid-vapor equilibrium in the absence of heat transfer.

The amount of heat transfer fluid 1 contained in the housing 2 can be between 25% and 80% of the total volume of the housing 2. It depends on the intended application and the compromise adopted between the thermal performance of the system and the other constraints to be taken in consideration, such as the inclination or the degree of freedom desired on the placement of the hot springs. For example for certain applications, the amount of fluid may be between 30% and 70%, or between 40% and 60%, or between 45% and 55%, or even substantially equal to 50% of the total volume of the housing.

As will appear more clearly in the following text, the combination of this characteristic with specificities relating to the dimensioning of the housing 2 allows the thermal diffusion device to respond to the aforementioned constraints concerning the efficiency of the device at high flux density, its sensitivity tilt, simplicity, etc.

The material constituting the heat transfer fluid 1 can vary depending on the desired operating temperature level. The heat transfer fluid 1 can for example be an oil, an alcohol (such as methanol, ethanol or glycol), an organic compound (such as acetone, ammonia), a mixture, a nanofluid, a liquid metal, or any type of heat transfer fluid known to those skilled in the art.

In one embodiment, the heat transfer fluid 1 is demineralized water. The use of water as heat transfer fluid 1 has many advantages, and in particular:

- a very low cost and

- zero toxicity and

- flammability and

- excellent thermal performance.

1.2. Housing

The housing 2 comprises walls consisting for example of plates of thermally conductive material such as metal (for example copper or aluminum). The choice of material used to make the walls of the housing 2 depends in particular on the manufacturing and use constraints, as well as the type of heat transfer fluid chosen, the fluid / material couple of the housing having to be chemically compatible.

Housing 2 includes:

a bottom wall 21 forming the bottom,

an upper wall 22 opposite the lower wall 21,

- two transverse side walls 23, 24, and

- two longitudinal side walls 25, 26.

The walls 21-26 of the housing 2 are connected to each other so as to constitute a sealed reservoir containing the heat transfer fluid 1.

In the following text, the expressions “side wall”, “upper wall”, “lower wall” will be used, with reference to a rectangular parallelepiped.

The reader will appreciate that it is understood, within the framework of the present invention, by:

• "lower wall", a horizontal wall of a rectangular parallelepiped closest to the ground, • "upper wall", a horizontal wall of a rectangular parallelepiped opposite the lower wall, • "face / side wall", one face / vertical wall of a rectangular parallelepiped extending in a plane perpendicular to the lower wall, • "longitudinal faces / walls", vertical faces / walls of a rectangular parallelepiped of which at least one dimension is greater than the dimensions of the other faces / side walls, • "transverse faces / walls", vertical faces / walls extending perpendicular to the longitudinal faces / walls.

Advantageously, the housing 2 is devoid of capillary structure. This reduces the risk of degradation of the thermal diffusion device in the event of the heat transfer fluid 1 freezing, for example during prolonged deactivation of the device in a cold environment. The absence of a capillary structure also makes it possible to improve thermal performance and reduce the cost and manufacturing constraints compared to the capillary heat pipes commonly used.

1.2.1. Longitudinal side walls

The longitudinal side walls 25, 26 constitute the walls of larger dimensions of the thermal diffusion device. More specifically, the area of a longitudinal side wall is greater than the area of each of the other walls of the housing

2.

Housing 2 includes:

• a first longitudinal side wall 25, • a second longitudinal side wall 26 extending parallel to the first longitudinal side wall 25.

In the embodiment illustrated in Figures 1 to 3, the outer face of the first longitudinal side wall 25 is intended to be in thermal contact with one (or more) hot source (s). The external face of the second longitudinal side wall 26 is intended to be in thermal contact with one (or more) cold source (s). As a variant, the hot and cold sources can be arranged on the same longitudinal side wall, as long as certain rules, explained below, are observed.

The distance "e" between the longitudinal side walls (25, 26) is advantageously between% and 2 times the capillary length of the heat transfer fluid (1). The “capillary length” is a length scale characteristic of an interface (between two fluids) subjected to capillary forces and to gravity forces: for example, when the gravitational effects dominate, a bubble or a drop is flattened by the gravity and its radius is large compared to the capillary length. This characteristic length is an intrinsic property and therefore depends on the heat transfer fluid chosen for the thermal diffusion device as well as on the operating temperature; in the case of water at 20 ° C, the capillary length is 2.7 millimeters.

The fact that the distance e between the longitudinal side walls 25, 26 is between% and 2 times the capillary length of the heat transfer fluid 1 makes it possible to take advantage of the phenomena of confined boiling. The main difference between boiling in a confined environment and in an unconfined environment is that for low heat fluxes, the wall overheating is less significant in a confined environment than in an unconfined environment. This reflects the fact that a better coefficient of heat transfer is obtained. The more the space is confined, the greater the exchange coefficient becomes compared to that reached during boiling in an unconfined environment.

Those skilled in the art generally consider that the confinement of boiling is not suitable in the context of significant heat fluxes. In fact, he considers that in the event of a significant thermal flux in a confined environment, the rate of vapor produced becomes significant and taking into account the small dimensions characteristic of the system, this leads to a deterioration in thermal performance, in particular linked to pressure problems and possibly until the diffuser stops operating.

The inventors have discovered that the combination:

• a quantity (Qf) of heat transfer fluid between 25% and 80% of the total volume (Vtot) of the housing, and • a distance e of between% and 2 times the capillary length (L _c ) of the heat transfer fluid makes it possible to obtain an effective thermal diffusion device, even when the thermal flux is high and to increase the surface available for the placement of the hot springs.

The combination of these characteristics (% xL _c <e <2xL _c , and ³ / ioxVt0t <Qf < ⁷ / ioxVt0t) allows:

• to improve the thermal performance of the device, • to limit the constraints on the positioning of the hot springs, and ίο • to reduce the sensitivity to the inclination of the thermal diffusion device.

1.2.1.1. Spacers and Fixing Means

In one embodiment, the device comprises spacers 36 between the first and second longitudinal side walls 25, 26. These spacers 36 are fixed in different positions of the respective surfaces of the first and second longitudinal side walls 25, 26.

The spacers 36 can be fixed to the first and second longitudinal side walls 25, 26 by welding, brazing or gluing.

The presence of spacers 36 makes it possible to stiffen the housing 2 so as to keep the distance between the first and second longitudinal side walls 25, 26 constant.

Advantageously, the device can also include fixing means 35 - such as bolts or screws - to allow the fixing of one (or more) extinguisher system (s) on the diffuser, such as fins or a electronic card.

One (or more) spacer (s) 36 can (can) advantageously be arranged (s) so as to cooperate with a respective fixing means.

For example in the embodiment illustrated in Figures 1 to 3, blind holes are formed in the spacers 36 through the first longitudinal side wall to form tapped drums - four in number.

Each barrel 36 is intended to receive the thread of a respective fixing means to allow the fixing of a hot or cold source.

Advantageously, the spacers and fixing means 35, 36 of the first and second longitudinal side walls 25, 26 constitute thermal bridges which make it possible to heat the heat-transfer fluid 1 more quickly, for example in the event of freezing thereof (when the device heat diffusion is deactivated and the outside temperature is lower than the solidification temperature of the heat transfer fluid).

Thus, the presence of fixing means and spacers 35, 36 between the longitudinal side walls 25, 26 makes it possible to reduce the priming time of the device.

The term "priming duration" means the time interval between the moment when the heat dissipated by the element to be cooled is applied to the thermal diffusion device, and the moment when the heat transfer fluid 1 reaches a speed permanent flow.

By reducing the priming time of the device thanks to the fixing means and spacers, the risks of deterioration of the element to be cooled are limited, the priming time being short enough to guarantee effective cooling of the element to be cooled.

1.2.1.2. Texturing

In one embodiment, one of the two internal faces or the two internal faces of the longitudinal side walls 25, 26 are textured. In the case where the internal face of a single longitudinal side wall is textured, it will advantageously be the internal face of the first longitudinal side wall 25 intended to be in thermal contact with one (or more) hot source (s) (s).

This increases the exchange surface between the heat transfer fluid and the hot / cold source (s). In particular, the texturing:

• the internal face of the second longitudinal side wall 26 makes it possible to promote the phenomenon of condensation of the heat-transfer fluid 1, • the internal face of the first longitudinal side wall 25 makes it possible to promote the phenomenon of evaporation of the heat-carrying fluid 1 by promoting nucleation effects.

In the embodiment illustrated in FIGS. 1 to 3, the surface texturing of the internal faces of the longitudinal side walls 25, 26 consists of a vertical grooving produced on said internal faces, said grooves extending between the lower and upper walls 21, 22 of the device.

1.2.1.3. Hot spring positioning area

As indicated previously, the external face of the first longitudinal side wall 25 is intended to be in thermal contact with one (or more) hot source (s).

In the positioning zone 32 of the hot sources - called "evaporation zone" - the heat transfer fluid 1 is intended to be vaporized (i.e. passage from the liquid state to the vapor state) to allow the cooling of the hot sources.

In the embodiment illustrated in FIG. 1, the area of the evaporation zone is less than 40% of the total area of the first longitudinal side wall 25.

In the embodiment illustrated in FIG. 1, the distance between:

• the evaporation zone 32 and each transverse side wall 23, 24 is equal to one fifth of the length (L) of the first longitudinal side wall 25 ( ^L / s), the distance between • the evaporation zone 32 and the upper wall 22 is equal to one third of the height (H) of the first longitudinal side wall 25 (%), and the distance between the • evaporation zone 32 and the lower wall 21 is zero.

The distance between the evaporation zone 32 and each transverse side wall 23, and the distance between the evaporation zone 32 and the upper wall 22 depend on the intended application: they are a function of the quantity of heat transfer fluid 1 chosen as well only surfaces necessary for condensation and recirculation of the fluid.

At least one hot source is in thermal contact with a region of the external face of the first longitudinal side wall 25 for which the opposite internal face is covered with heat-transfer fluid 1 (advantageously so that the distance between the lower part of the corresponding region on the external face of the first longitudinal side wall 25 and the bottom wall 21 is zero).

This makes it possible to ensure the proper functioning of the thermal diffusion device, even for high flux densities, by keeping one or more surfaces free from hot sources on the external face of the first longitudinal side wall 25 in order to allow condensation and the return of the liquid to the evaporation zone 32.

Advantageously, the external face of the first longitudinal side wall 25 may include a positioning mark to indicate the location of (and delimit) the evaporation zone. This makes it easier for the user to position the hot springs. The positioning mark may consist, for example, of an imprint drawn or engraved on the external face of the first longitudinal side wall 25.

1.2.1.4. Cold source positioning area

In the embodiment illustrated in Figures 1 to 3, the outer face of the second longitudinal side wall 26 is intended to be in thermal contact with one (or more) cold source (s).

In the cold sources positioning zone - called "condensation zone" - the heat transfer fluid is intended to be condensed (i.e. transition from the vapor state to the liquid state).

The condensation zone can cover all or part of the surface of the external face of the second longitudinal side wall 26.

Alternatively, the condensation zone and the evaporation zone can extend over the same longitudinal side wall. In this case, the condensation zone extends above the evaporation zone. More specifically, the condensation zone can be arranged so that the distance between:

• the condensation zone and each transverse lateral wall 23, 24 is zero, the distance between • the condensation zone and the upper wall 22 is zero, and the distance between • the condensation zone and the lower wall 21 is equal to two third of the height (H) of the second longitudinal side wall 26 ( ² %).

Being able to vary the position and dimensions of the condensation zone makes it possible to limit the size of the device according to the intended application.

1.2.2. Transverse side walls

The transverse side walls 23, 24 extend perpendicular to the longitudinal side walls 25, 26. The length of each of these transverse side walls 23, 24 is equal to the height of the thermal diffusion device (which depends on the intended application) . The width of each of the transverse side walls is itself equal to the sum of the thicknesses of the longitudinal side walls added to the distance "e" between the longitudinal side walls 25, 26.

In other words, the width of each transverse lateral wall 23, 24 is between:

• twice the thickness of a longitudinal side wall plus% times the capillary length of the heat transfer fluid 1, and • twice the thickness of a longitudinal side wall plus twice the capillary length of the heat transfer fluid 1.

2. Principle of operation

We will now describe in more detail the operating principle of the thermal diffusion device with reference to FIGS. 4 and 5.

2.1. Out of operation

Referring to Figure 4, there is illustrated an embodiment of the device when the elements to be cooled do not generate heat.

The housing comprises an amount of heat transfer fluid substantially equal to 50% of its total volume, so that the lower half of the internal faces of the longitudinal and transverse side walls are immersed under the heat transfer fluid.

It is assumed in this embodiment that:

• the hot sources are arranged in the evaporation zone 32 of the first longitudinal side wall 25, at least one of the hot sources being in thermal contact with a region of the external face of the first longitudinal side wall 25 for which the opposite internal face is covered with heat transfer fluid 1, • the cold source is in thermal contact with the external face of the second longitudinal side wall 26 in the condensation zone.

2.2. Operating

When the elements to be cooled (i.e. hot springs) are activated, the heat generated at the hot springs is transmitted to the heat transfer fluid 1 via the first longitudinal side wall 25.

The texturing of the internal face of the first side wall 25 promotes the evaporation of the heat transfer fluid 1 by promoting nucleation phenomena. Thus, vapor bubbles 4 form in the heat transfer fluid (boiling) and rise towards the surface of said fluid (cf. FIG. 5). The evaporation of the heat transfer fluid 1 in the liquid state absorbs heat. This induces cooling of the hot source.

The ascent of the confined vapor bubbles 4 towards the surface of the heat-transfer fluid 1 makes it possible to raise the heat-transfer fluid in the liquid state ("pushed" by the bubbles below) so as to wet the evaporation zone 32 over its entire surface .

The heat transfer fluid vapor occupies the upper part of the housing 2. Once in the condensation zone, the heat transfer fluid in vapor form is transformed into liquid (phenomenon of condensation), then falls via recirculation zones (corresponding to zones in the housing extending opposite regions of the external face of the first longitudinal side wall 25 devoid of hot sources) towards the lower wall 21 of the housing 2 under the effect of gravity.

3. Conclusions

The proposed thermal diffusion device is capable of transferring heat from one or more planar hot sources - such as a card or an electronic component - to a cold source - such as a radiator. Typical dimensions for electronic component cooling applications can be:

• a few centimeters (or ten centimeters) for the length (L) and the height (H) of the longitudinal side walls, and • a few millimeters for the distance (e) between the longitudinal side walls.

The thermal diffusion device comprises:

• one (or more) possible zone (s) for positioning the hot source (s), called "evaporation zone (s)", and • one (or more) zone (s) possible positioning of the cold source (s), called "condensation zone (s)".

The evaporation and condensation zones can be placed on opposite walls (in particular the longitudinal side walls) or on the same wall.

The device can be used in vertical or tilted position (even strongly). A great flexibility is allowed in the positioning of the sources. At least one of the hot springs is located below the filling level of the housing 2 with heat transfer fluid 1 to promote the evaporation of the latter. Furthermore, the hot springs are preferably positioned so that:

• the distance between the hot springs and the upper wall 22 of the housing 2 is greater than or equal to one third of the height of the side walls 23-26 of the housing 2, and so that • the distance between the hot springs and the side walls transverse 23, 24 of the housing 2 is greater than or equal to one fifth of the length of the longitudinal side walls 23, 24.

This maximizes the heat diffusion efficiency of the device.

The reader will have understood that numerous modifications can be made to the device described above without materially departing from the new teachings and the advantages described here.

Therefore, all such modifications are intended to be incorporated within the scope of the appended claims.

Claims (9)

1. Heat diffusion device with heat pipe effect comprising a heat transfer fluid (1) and a housing (2), the housing (2) having a bottom wall (21) forming the bottom, an upper wall (22) opposite the bottom wall ( 21) and four side walls (23, 24, 25, 26) between the lower (21) and upper (22) walls, the side walls consisting of: - two transverse side walls (23, 24), - two longitudinal side walls (25, 26), a first longitudinal side wall (25) being intended to receive a hot source, characterized in that: the distance between the longitudinal side walls (25, 26) is between% and 2 times the capillary length of the heat transfer fluid (1), - The quantity (Qf) of heat transfer fluid (1) contained in the device is between 25 and 80% of the total volume (Vtot) of the housing (2). 2. Device according to claim 1, which is devoid of capillary structure. 3. Device according to any one of the preceding claims, in which the hot source is intended to be positioned in an evaporation zone (32) of the first longitudinal side wall (25), the area of the evaporation zone. (32) being less than 40% of the total area of the first longitudinal side wall (25). 4. Device according to the preceding claim, in which the position of the evaporation zone on the first longitudinal side wall is such that: • the distance between the evaporation zone (32) and each transverse side wall (23, 24) is greater than or equal to one fifth of the length (L) of the first longitudinal side wall (25), • the distance between the evaporation zone (32) and the upper wall (22) is greater than or equal to one third of the height (H) of the first longitudinal side wall (25), and • the distance between the evaporation zone (32) and the bottom wall (21) is zero. 5. Device according to any one of the two preceding claims, in which the external face of the first longitudinal side wall (25) comprises a positioning mark to define the position of the evaporation zone (32). 6. Device according to any one of the preceding claims, which comprises spacers (36) between the internal faces of the longitudinal side walls (25, 26) of the housing (2), each spacer (36) being intended to cooperate with means respective fixing. 7. Device according to any one of the preceding claims, in which the internal faces of the longitudinal side walls (25, 26) comprise a surface texturing. 8. Device according to the preceding claim, wherein the surface texturing consists of grooves formed on the internal faces of the longitudinal side walls (25, 26), the grooves extending between the lower and upper walls (21,22) of the housing (2). 9. Device according to one of claims 1 or 2, wherein the heat transfer fluid (1) is water. 1/3 2/3 e