WO2008009811A1

WO2008009811A1 - Heat flow device

Info

Publication number: WO2008009811A1
Application number: PCT/FR2007/001222
Authority: WO
Inventors: Emile Colongo; Stéphane ORTET
Original assignee: Airbus France
Priority date: 2006-07-18
Filing date: 2007-07-17
Publication date: 2008-01-24
Also published as: CA2657777C; US20090283251A1; RU2009105499A; FR2904102B1; CN101490496A; JP2009543997A; CA2657777A1; EP2044381A1; BRPI0713193A2; EP2044381B1; FR2904102A1; RU2465531C2

Abstract

A device comprises equipment (501) with a heat source having a maximum thermal operation condition, a cold part (502) relative to the equipment and an element (503) capable of transmitting the heat from the equipment to the cold part. The element (503) is capable of causing the transmitted heat to be limited for thermal conditions above a specified threshold below said maximum condition.

Description

t

Heat flow device

The invention relates to a heat flow device.

In such a device, it is sought to evacuate the thermal energy (or heat) dissipated at the equipment level by any heat source (for example an electrical circuit or an electronic component).

Classically connected to do this the equipment to a cold part relative thereto, which plays the role of a cold source, by means of a heat conductive element.

Thus, a quantity of heat flows through the conductive element, with a power inversely proportional to the thermal resistance thereof, which allows to evacuate at least a portion of the heat generated at the equipment and therefore avoid excessive heating of it.

For example, the patent application US 2003/0196787 uses this technique and proposes, for reasons related to the operation of the equipment, to reduce this evacuation of the heat at low temperature.

The inventors realized that these solutions could present risks in practice, in particular when the cold-source portion is not adapted to all the conditions of temperature and / or heat dissipation, as is the case for example. example when this cold part is formed of a combustible material or sensitive to temperature rises.

In order to avoid such problems, the invention proposes a device comprising equipment with a heat source having a maximum thermal operating condition, a cold part relative to the equipment and an element able to transmit the heat of the equipment. in the cold part, characterized in that the element is able to cause a limitation of the heat transmitted for thermal conditions greater than a determined threshold below said maximum condition. Thus, the heat generated in the equipment is no longer completely transmitted (or almost no longer transmitted) to the cold part when these thermal conditions are encountered (that is to say, for example when the temperature or the thermal power transmitted through the element exceeds said threshold) and overheating thereof is avoided.

The thermal conditions correspond for example to a thermal power transmitted through the element. In this case, the element can limit the transmitted thermal power to the value of said determined threshold

The equipment and the cold part can moreover be essentially separated by a gaseous blade, at least in said thermal conditions, in order also to avoid under these conditions the transmission of electrical phenomena (such as electric arcs), in particular propagation. electric arcs, equipment to the cold source.

The equipment and the cold part are for example separated by said blade whatever the thermal conditions and the element may then comprise at least one heat pipe passing through said blade.

In this context, we take advantage of the limitation of the thermal power that can transmit the heat pipes, past a certain threshold, to limit the thermal power transmitted by the element to this threshold.

According to another possible solution, the element comprises at least one component of which a change of state (for example a transition from the liquid state to the gaseous state) in said thermal conditions causes the increase of the thermal resistance; which also limits the amount of heat transmitted. Here we take advantage of the increase in thermal resistance generally related to such a change of state. The component can then form said blade after said change of state, which is a practical way to obtain this blade.

According to another conceivable embodiment, the element is configured to lose contact with the equipment or the cold part in said thermal conditions. It is in this case the breaking of the contact between the different parts which causes the interruption of the thermal path between the equipment and the cold part, and therefore the limitation of heat transmission.

The element comprises for example in this case at least one component, a change of state in said thermal conditions causes said loss of contact.

It can be provided in this context that said component participates in the conduction of the equipment to the cold part outside said thermal conditions and is erased because of its change of state in said thermal conditions, thus essentially isolating the equipment and the cold part.

According to another approach, which may optionally be combined with the previous one, the change of a mechanical property of the component during its change of state may cause a movement of a part of the element, thus causing said loss of contact.

In these cases also, the element can be configured so that the change of state of the component allows the formation of said gaseous blade. The change of state then makes it possible not only to interrupt the thermal path, but also to avoid the propagation of electrical phenomena.

In this context, the change of state may be a transition from the solid state to the liquid state, or a transition from the liquid state to the gaseous state.

The equipment may be a fuel pump and the cold part a liquid fuel, for example in an aircraft; the invention is particularly interesting in this context, although it naturally has many other applications, such as the protection against overheating of heat sink elements sensitive to temperature rises, such as carbon structures.

The arrangements proposed above, optionally for some, thus allow in particular to evacuate the heat produced by the equipment, for example electronic as in the case of fuel pumps, while avoiding overheating of the heat sink (for example the fuel), thanks to the limitation of the transmitted heat, as well as the propagation of electric arcs from the equipment to this well.

The invention also proposes an aircraft equipped with such a device.

Other features and advantages of the invention will emerge in the light of the following description given with reference to the appended drawings in which:

- Figures 1A to 1C show a first embodiment of the invention;

FIGS. 2A to 2C show a second embodiment of the invention;

- Figures 2D to 2F show a variant of the second example shown in Figures 2A to 2C;

FIGS. 3A to 3C show a third embodiment of the invention;

FIGS. 4A to 4C show a fourth embodiment of the invention;

- Figures 5A and 5B show a fifth embodiment of the invention.

FIG. 1A represents a first exemplary embodiment of the invention in normal operating mode.

In this example, a hot plate 101 which comprises a heat source (not shown) is connected to a cold plate 102 (for example a part of the device structure) by means of a solid material 103 at the nominal temperature T _{n 0} min corresponding to normal operation.

The material 103 is a thermal conductor and its thermal resistance R _mate _ri u is therefore relatively low. Thus, the heat generated by the heat source at the hot plate 101 is removed, under normal operating conditions, through the material 103 to the cold plate 102 which acts as a heat sink or cold source .

The material 103 is also chosen such that its melting temperature Tfusion is less than or equal to the desired maximum operating temperature T _max . Such a maximum temperature can be for example, to avoid a degradation of the cold plate 102, or other negative consequences, such as a fire risk when the cold plate is made in the form of a combustible material such as the fuel of an aircraft.

Thus, as shown in FIG 1B, when the temperature T of the material reaches 103, for example due to an output of the normal operation, the melting temperature T j _was _0n the material 103, it changes state the material 103 passes from the solid state to the liquid state (represented under the reference 103 'in FIG. 1B), which causes it to be erased (here its flow by appropriate means) from its initial position in contact with the plate hot 101 and the cold plate 102.

Therefore, when the temperature between the plates 101, 102 is greater than the desired maximum temperature T _max , the hot plate 101 and the cold plate 102 are no longer connected by the material but separated by an air knife 106 whose The thermal resistance R _a ir is much greater than that of the material Rmaterial, as shown in FIG. 1C.

The cold plate 102 is then thermally insulated from the hot plate 101 by means of the air knife 106 which separates them; the latter also plays the role of an electrical insulator, which also prevents the transmission of electrical energy (for example in the form of electric arcs) from the hot plate to the cold plate 102. This last advantage is particularly interesting in the case where the hot plate 101 comprises an electrical or electronic equipment whose possible malfunctions could be dangerous at the cold plate 102 especially when it has reached a temperature above the desired maximum temperature T _max .

For example, wax material whose heat properties permit a conduction of heat that is much greater than that permitted by the thermal resistance of air 106 is used as material.

FIG. 2A represents a second exemplary embodiment of the invention in normal operating mode, that is to say, for example at a operating temperature T _n0 minai significantly lower than a desired maximum temperature.

In this example, a device 201 comprising a heat source is located at a distance from a cold plate 202 and consequently separated therefrom by an air knife 206. The equipment 201 is also linked to the cold plate. 202 by means of a heat sink 203 formed in a material that is a good conductor of heat (that is to say of low thermal resistance) and which therefore extends partly in the space formed by the air space 206

The heat sink 203 is held in contact with the cold plate 202 by interposition between a part of the equipment 201 and the conductive drain 203 of a solid state bonding material 204. Furthermore, a compression spring 205 is interposed between the drain 203 and the cold plate 202, the spring 205 being compressed when the drain 203 is in contact with the cold plate 202.

The drain 203 is connected to the equipment 201, on the one hand through the connecting material 204 and on the other hand directly to other parts of the equipment 201 that those receiving the connecting material 204, for example to the level of a side wall 208 of the equipment 201.

When the temperature at the bonding material 204 increases beyond the normal operating regime and reaches the fusing temperature T _fUS ion of the bonding material 204, the latter passes from the solid state to the liquid state (as shown in _FIG. in Figure 2B where the bonding material in the liquid state is referenced 204 ') and flows out of the device by appropriate means.

As a result, the drain 203 is no longer held in contact with the cold plate 202 but instead moves away under the effect of the spring 205. Due to the displacement of the drain 203 and its loss of contact with the plate cold 202, the equipment 201 and the cold plate 202 are separated by the thickness (or blade) of air 206, except the spring 205 whose thermal conductivity is negligible, and these two elements are essentially isolated by means of the air gap 206, as shown in Figure 2C. FIG. 2D represents, in normal operating mode, a variant of the second example which has just been described.

As for the second example previously described, a device 211 comprising a heat source is located at a distance from a cold plate 212 and therefore separated therefrom by an air knife 216. The equipment 211 is also linked to the cold plate 212 by means of a heat sink 213 formed in a material of low thermal resistance and which therefore extends in part in the space formed by the air knife 216

According to this variant, the heat sink 213 is however held in abutment against the cold plate 212 by means of a solid block 214 interposed between the conductive drain 213 and a structural part 210. Moreover, as for the second example, a spring compression 215 is interposed between the drain 213 and the cold plate 212, the spring 215 being compressed when the drain 213 is in contact with the cold plate 212 due to the presence of the solid block 214.

Thus, according to the present variant, the solid block 214 does not necessarily participate in the flow of heat.

When the temperature at the solid block 214 increases beyond the normal operating regime and reaches the melting temperature T melt of the material constituting the block 214, the latter passes from the solid state to the liquid state (as shown in FIG. 2E where the molten block is represented as 214 ') and flows out of the device by appropriate means.

As a result, the drain 213 is no longer held in contact with the cold plate 212, but instead moves away under the effect of the spring 215. Due to the displacement of the drain 213 and its loss of contact with the plate 212, the equipment 211 and the cold plate 212 are separated by the thickness (or blade) of air 216, except the spring 215 whose thermal conductivity is negligible, and these two elements are essentially isolated by means of there air slide 216.

According to the embodiment shown in FIG. 2F, the displacement of the drain 213 then continues until it comes into contact with the part of structure 210 which could then in this case in turn function as a heat sink.

Figure 3A shows a third embodiment of the invention under normal operating conditions.

According to this example, the equipment 301 generating heat and the cold part 302 acting as cold source are respectively located in the upper part and the lower part of an enclosure 305.

A space in the enclosure between the equipment 301 and the cold part 302 is filled with a liquid-form bonding material 303 having a low thermal resistance and which forms a heat conduction path between the equipment 301 and the cold part 302.

The enclosure 305 receives the equipment 301, the connecting material 303 and the cold part 302 hermetically. Only a safety valve 304 penetrating into the chamber at the space filled by the connecting material 303 possibly allows evacuation of the liquid when the pressure is greater than a threshold as explained below.

The bonding material 303 is such that its vaporization temperature corresponds approximately (and is preferably slightly less) to a desired maximum temperature at the cold portion 302.

Therefore, when, for example due to a malfunction of the equipment 301, the temperature of the bonding material exceeds the vaporization temperature (and thus reaches the desired maximum temperature), the bonding material 303 passes from the liquid state in the gaseous state during a phase shown in Figure 3B (the gaseous material 303 'naturally occurring in the upper part of the space of the chamber 305 previously occupied by the liquid, in contact with the equipment 301).

The change of state in the hermetic enclosure 305 causes a rise in pressure inside thereof until the pressure reaches the tripping threshold of the safety valve 304 and that the liquid part of the material of Link 303 therefore begins to drain as shown in Figure 3B. If the temperature continues to increase beyond the vaporization temperature of the bonding material 303, the phenomenon just described and shown in FIG. 3B continues until the space of the enclosure 305 located between the equipment 301 and the cold part 302 is completely filled with the gas phase 303 'of the connecting material.

The thermal path initially formed by the bonding material 303 in liquid form is therefore interrupted and the cold part 302 is thereby thermally insulated from the equipment 301, the thermal resistance of the gaseous bonding material being much greater than that of the binding material in liquid form.

It is noted that the phase change (that is to say the transition from the liquid state to the gaseous state) of the connecting material has also made it possible to replace the thermal path with a gaseous blade, which makes it possible, in particular, to avoid arcing between the equipment 301 and the cold part 302.

FIG. 4A represents a fourth embodiment of the invention under normal operating conditions, that is to say for temperatures (whose nominal operating temperature) that are well below a maximum permitted temperature.

In this exemplary embodiment, an enclosure 405 is formed in the lower extension of a hot plate 401 (which is for example a part of an equipment containing a heat source, such as for example a fuel pump equipping the aircraft) .

The enclosure 405 is hermetic and comprises in its lower part, in normal operating mode, a liquid component 403.

A heat sink 404 is also partially received inside the enclosure 405: an upper portion 406 (here substantially horizontal) extends over the entire (here horizontal) surface of the enclosure 405 so as to form a piston separating an upper part of the enclosure 405, for example filled with air, from a lower part of the enclosure 405 filled by the liquid component 403 in normal operating mode. It can thus be considered in normal operation that the drain floats on the liquid component 403.

The heat sink 404 also comprises a rod (here essentially vertical), a lower part 407 of which, in normal operation as illustrated in FIG. 4A, is in contact with a cold part forming a heat sink, here formed by the liquid fuel 402 of the aircraft. The lower portion 407 is precisely in this case immersed in the fuel 402 as shown in Figure 4A.

In the normal operating configuration shown in FIG. 4A (that is to say, in particular for the nominal operating temperature), a thermal path is thus formed between the equipment 401 and the cold part 402 by means of materials having a relatively low thermal resistance, namely here the walls of the enclosure 405, the liquid component 403 and the heat sink 404.

When the temperature in the enclosure 405 rises above the nominal operating temperature (for example, because of a malfunction of the equipment 401) and reaches the vaporization temperature of the liquid component 403 (preferably chosen slightly lower than a maximum allowed temperature inside the enclosure 405, which corresponds for example to a temperature beyond which there are risks due to the presence of the fuel 402), a gaseous phase 403 'appears in the lower part of the enclosure 405 and the pressure it exerts tends to move up the heat sink 404 which is recalled that the upper portion 406 piston shape, as shown in Figure 4B.

Thus, the movement of the heat sink 404 produced under the effect of the pressure, itself due to the change of state of the liquid component 403, causes the vertical part of the heat sink, at least partly outside the cold part 402, which limits the heat transfer to this cold part and avoids overheating thereof.

If, however, the temperature still rises above the vaporization temperature of the liquid component 403, the whole of it becomes gas and the pressure exerted in the lower part of ^

the enclosure 405 increases so that the drain 404 is driven upward until its lower portion 407 emerges from the cold source fuel 402 and ends its travel away from it.

In this final position, the space between the lower part 407 of the drain 404 and the surface of the liquid fuel 402 is filled with a blade of a thermally and electrically insulating gas (such as for example air) in such a way that that the equipment 401 and the liquid fuel 402 forming a cold source are sufficiently thermally and electrically insulated to avoid any risk of fire fuel 402.

FIG. 5A represents a fifth example of implementation of the invention.

According to this fifth example, an equipment comprising a heat source (or hot plate) 501 is separated from a cold plate 502 (for example a structural element of an aircraft) by means of an air knife 504 in order to avoid the propagation of arcing between the equipment 501 and the cold plate 502.

A plurality of heat pipes (or heat pipes) 503 (two of them in FIG. 5A) pass through the air gap 504, each heat pipe 503 being at one end. in contact with the equipment 501 and at the other end in contact with the cold plate 502. Alternatively, it is possible to use a single heat pipe when the dimensioning of the heat flows in the device allows it.

The heat pipes, made for example in the form of two-phase tubes, make it possible to evacuate to the cold plate 502 the heat generated within the equipment 501, and this in normal operation, that is to say when the power transmitted by the heat pipes (or alternatively the temperature thereof) does not exceed a power threshold P _seU ii (temperature respectively). (Here, the term temperature threshold is an absolute value of temperature or a relative value, for example with respect to the temperature outside the heat pipe.)

The heat resistance R _th of the heat pipes 503 is therefore relatively low as long as the thermal power that flows through them is below the threshold Pseuϋ (respectively as long as the temperature is below the temperature threshold).

The heat pipes 503 are, however, such that, when the thermal power therethrough is greater than this threshold P _seU ii (respectively when the temperature is greater than the temperature threshold), their thermal resistance R _th increases sharply, as illustrated in FIG. 5B.

In these thermal conditions (which correspond to operating conditions of the heat pipes different from the usual conditions), that is to say when this threshold of transmitted thermal power is reached (output of the normal operation of the heat pipe), the power transmitted by the heat pipe is limited to this threshold value.

Thus, even if the equipment generates a thermal power greater than the power threshold of the heat pipe, the latter saturates and therefore transmits to the cold plate a limited thermal power, which avoids overheating thereof. In this way, the heat evacuation is continued in part, but without risk for the cold plate.

The above embodiments are only possible examples of implementation of the invention which is not limited thereto.

Claims

Device comprising an equipment with a heat source having a maximum thermal operating condition, a cold part relative to the equipment and an element capable of transmitting the heat of the equipment to the cold part, characterized in that the element is capable of causing a limitation of the heat transmitted for thermal conditions greater than a determined threshold lower than said maximum condition.

2. Device according to claim 1, wherein the thermal conditions correspond to a thermal power transmitted through the element.

3. Device according to claim 2, wherein the element is adapted to limit the transmitted thermal power to the value of said determined threshold.

4. Device according to one of claims 1 to 3, wherein the equipment and the cold part are essentially separated by a gaseous blade at least in said thermal conditions.

5. Device according to claim 4, wherein the equipment and the cold part are separated by said blade regardless of the thermal conditions and wherein the element comprises at least one heat pipe passing through said blade.

6. Device according to one of claims 1 to 5, wherein the equipment is a fuel pump.

7. Device according to one of claims 1 to 6, wherein the cold part is a liquid fuel.

8. Device according to one of claims 1 to 6, wherein the cold part is an element sensitive to temperature rises.

9. Aircraft equipped with a device according to any one of claims 1 to 8.