WO2009010390A1

WO2009010390A1 - Fuel cell system with temperature control means having a phase change material

Info

Publication number: WO2009010390A1
Application number: PCT/EP2008/058535
Authority: WO
Inventors: Frank Baumann; Florian Wahl; Sebastian Maass
Original assignee: Robert Bosch Gmbh
Priority date: 2007-07-18
Filing date: 2008-07-02
Publication date: 2009-01-22
Also published as: DE102007033428A1

Abstract

The present invention relates to a fuel cell system, having a fuel cell stack and associated temperature control means with a phase change material. The invention is characterized in that the temperature control means have at least one element which is separated from the functional elements of the fuel cell stack and is associated with an outer surface of the fuel cell stack in a planar, heat-conducting manner.

Description

description

title

Fuel cell system comprising a tempering agent comprising a phase change material

The present invention relates to a fuel cell system comprising a tempering agent comprising a phase change material according to the preamble of claim 1.

State of the art

When operating commercially available fuel cells, water is produced which, after switching off the fuel cells, remains in the fuel cell stack and can freeze under corresponding ambient conditions. This makes the reboot much more difficult and the start time of the

Fuel cell system can be extended. In particular, there is also the risk that frozen product water closes the inputs and / or outlets of the fuel cell stack and, as a result, a dangerous increase in pressure in the fuel cell system may result.

Purpose and advantages of the invention

The present invention is therefore an object of the invention to improve a fuel cell system of the type set forth. The solution of this object is achieved by the features of claim 1. In the subclaims expedient and advantageous developments are given.

Accordingly, the present invention relates to a

A fuel cell system comprising a fuel cell stack and associated therewith, a phase change material comprising tempering. The fuel cell system is characterized in that the tempering means comprise at least one separate from the functional elements of the fuel cell stack, an outer surface of the fuel cell stack heat-conducting associated element and can influence the fuel cell stack from its outside in its temperature. Functional elements of the fuel cell stack are at least z. B. anode, cathode, membrane, pole plates and the like.

A phase change material often has an abrupt transition between two phases, for example the solid and the liquid phase. For heat storage is the

Phase change material by means of heat transfer from one phase to another phase, usually from a solid or crystalline phase to a liquid or dissolved phase. Unless further action is taken on the phase change material, the material retains its latter phase, even if it cools. In the changed phase, ie liquid or gas of the material, heat energy is stored latently, ie hidden. The release of the stored heat energy is effected by deliberately introducing a slight electrical, mechanical or chemical change into the phase change material. When using a salt solution as a phase change material, this z. B. be an exposure of crystalline surfaces. After the phase transformation has been triggered, the phase change material changes from its liquid or dissolved phase into a solid or crystalline phase in a short time, the previously stored heat energy being released. In particular, at low ambient temperatures, the fuel cell stack can be protected against massive cooling depending on the embodiment over part of the area or over the entire surface or, after cooling by the surface thermally conductive associated element over a large area, quickly and easily be brought back into a specific temperature range. The areal thermally conductive element can thus act primarily as temperature control means for supplying heat to and / or for dissipating heat away from the fuel cell stack, and additionally additionally as insulation with respect to the surrounding area of the fuel cell stack. As a phase change material are z. As paraffins and salt hydrates.

In particular, it can be advantageous if one and / or a plurality of heat-conducting elements of the surface

Enclose fuel cell stack, in particular completely encase. Such encapsulation of

Fuel cell stack can be done, for example, by individual, planar elements that cover one side or part of one side of the fuel cell stack and include together with other such elements the fuel cell stack.

The arrangement of several such elements can be done in different versions. On the one hand, it is possible to disguise the fuel cell stack arranged side by side on its surface, surface heat conductive elements. In this case, a meshing of individual such elements or subsections of such elements is possible. As particularly advantageous it is considered, if the fuel cell stack associated side of such a surface thermally conductive element has complementary structures of the relevant fuel cell stack surface, so that the largest possible thermal contact surface with as little interposed insulating regions, z. B. by air, can be realized. As an alternative or in addition to a single-layer cladding of the fuel cell stack by one or more such areal thermally conductive elements, a further, additional enveloping layer can also be formed on the fuel cell stack, preferably again as completely as possible.

However, it may also be advantageous to coat only certain area of the fuel cell stack with a first and / or a second such areal heat-conducting layer. For example, these could be the areas of the inputs and / or outputs of the supply lines.

In a preferred embodiment, the planar heat-conducting element itself may comprise a phase change material. As a result, the energy intake or the

Energy release due to the phase change of the

Phase change material carried out directly on the fuel cell stack, so that losses can be excluded by intervening insulation and / or lines.

Another possible embodiment would be integrated into the

Stack, z. In every xth biplar plate.

Additionally or alternatively, the areal thermally conductive element may also be connected in a heat-conducting manner with another heat storage element comprising a phase change material. For this purpose, in particular, a heat exchanger, which is optionally connected via a fuel cell stack associated coolant circuit with the planar heat-conducting element is suitable. As a result, for example, the heat can be temporarily stored at a different location in terms of space consumption of the fuel cell stack and coupled in a heat-conducting manner via the respective lines. Another advantage may be that the heat storage capacity can be increased by two separately formed, each a phase change material comprising heat storage elements, also advantageous again without additional Space or space required directly on the fuel cell stack. In a further advantageous manner, a staggered energy control or energy state influencing / influencing the temperature is possible in the case of a plurality of heat storage elements with phase change material which are formed separately from one another.

In a further preferred embodiment, the temperature range for the phase change of the phase change material z. B. in the range of about 0 ° Celsius or slightly above. This allows the

If required, fuel cell stacks are either protected from such a temperature range before cooling down, or reheated to or above this temperature when the phase change of the phase change material is initiated, so that a rapid and unproblematic starting process of the fuel cell stack is possible even at low external temperature conditions, in particular at Temperatures <0 ⁰ C, can be guaranteed.

Alternatively or additionally, the temperature range for a phase change of the phase change material can also be approximately in the range of the maximum permissible coolant inlet temperature in the fuel cell stack or even slightly lower. This has the advantage that a large amount of heat from the fuel cell stack to the energy-storing phase change material can be dissipated without the critical coolant temperature of the fuel cell stack is exceeded. The goal is to catch temperature peaks.

For example, in one embodiment, the phase change material used for this purpose could be formed in the additional energy store and / or heat exchanger arranged away from the fuel cell stack. When the incoming refrigerant from the refrigeration cycle reaches this critical temperature, the phase transition of the phase change material takes place, e.g. B. from solid to liquid or from liquid to gaseous or even from solid to gaseous. The phase change requires a large amount of energy due to the latent energy of the phase transition. As a result, energy can be supplied integrally over a longer period of time, for. B. during a full load operation until the

Phase transition is complete. However, such influencing is, of course, also possible for phase transition materials arranged directly on the fuel cell stack.

Upon cooling, the phase change material keeps its phase, the stored heat energy is given off only slowly. In order to regenerate the latent heat storage to intercept the next peak load again, the stored heat by targeted initiation of the Kritallisation or sublimation, z. B. during a partial load operation, be discharged again. This further reduces the load spread of a coolant pump of a refrigeration cycle as the flow through the radiator and the fuel cell stack can be maintained in the partial load range at relatively high flow and the heat output of the phase change material maintains the coolant temperature and / or fuel cell stack temperature at a minimum level avoids excessive cooling of the fuel cell stack.

In order to influence the phase transitions of the and / or the phase transition materials, a control unit can be provided in a further advantageous embodiment. It is particularly preferred if this

Control unit is designed so that it can control both the upper and the lower phase change of the phase change material. For example, it may for this purpose be associated with a crystallization seed, which is excitable, for example, and triggers the phase change change with appropriate initiation.

If several, isolated from each other trained Phase control materials are provided, the control unit can influence the respective phase transitions in different modes, for example, based on certain operating conditions. For this purpose, for example, be determined via a query to a user, whether the transitions should be staggered, so that z. B. in intentional, early recommissioning of the fuel cell stack falls below a minimum temperature can be prioritized. In another operating mode, it may also be provided that all or at least a large part of the individual

Phase change materials are stimulated simultaneously to the phase change in order to achieve the highest possible energy transfer in the shortest possible time. For example, this would be conceivable for a cold start, but also with an impending overheating of the fuel cell system.

In a particularly advantageous manner, the control unit can be designed such that it initiates a phase change of the phase change material before and / or during a start phase of the fuel cell stack. As a result, the fuel cell stack can be brought into its optimum operating temperature range much faster, if necessary by cooling by supplying the appropriate amount of heat.

In addition supportive can be provided in an advantageous manner an insulation for the planar heat-conducting element, which is particularly advantageously formed on a side facing away from the fuel cell stack. This insulation can thus additionally protect the fuel cell stack to the outside against strong temperature fluctuations. But also for a thermally conductive compounds, such. B. a cooling circuit connected units, such. As the above-mentioned heat exchanger can be isolated in an advantageous manner with an insulation for the temperature stabilization. embodiment

The invention will be explained in more detail with reference to the drawings and the description below. Show it

Fig. 1 to 4 each an example

Fuel cell system with a fuel cell stack with different embodiments of him assigned, surface heat-conducting elements

5 shows a further embodiment of a fuel cell system with an additional heat exchanger connected to a cooling circuit for a fuel cell stack.

FIG. 1 shows, by way of example, a fuel cell system 1 with a fuel cell stack 2, which is encased in a planar heat-conducting element of a temperature control medium comprising a phase change material. In this embodiment, the heat-conducting element 3, which is formed separately from the functional elements of the fuel cell stack and has an outer surface 11 of the fuel cell stack, is itself a phase change material 4. Thus, the fuel cell stack 2, depending on the embodiment, at low ambient temperatures before cooling below a range of 0 ⁰ C or something over it by initiating a phase transition and feeding the resulting heat released in the fuel cell stack are protected, so that water therein do not freeze can. In another embodiment, alternatively or additionally is done

Below this freezing temperature for water, a rapid supply of a large amount of energy in the fuel cell stack possible to re-thaw frozen water therein and so turn to shorten the cold start phase. Another advantage of the thawing of frozen water lies in the exposure of possibly frozen connections of supply lines or discharges of the fuel cell stack, so that otherwise possibly resulting overpressure conditions can be avoided therein.

As a further thermal protection of the fuel cell stack is an insulation 5, here also exemplifies the fuel stack 2 and enclosing it enclosing large area thermally conductive element 3, shown. As a result, the fall in the internal temperature can be additionally slowed down with falling outside temperatures.

For the controlled initiation of a phase transition, in particular for the release of the heat stored in the phase change material, a control unit 7 is further exemplified, which is connected via a line 8 with a z. B. electrically energizable crystallization nucleus is connected to the corresponding signal of the

Control unit 7 triggers the phase change in the phase change material. This trigger signal, the control unit z. B. depending on the operating state of the fuel cell system 1 on the one hand to support the starting process of the crystallization nucleus, and on the other hand to release storage capacity and optionally to stabilize an ideal operating temperature of the fuel cell stack, for example, in its partial load operation.

FIG. 2 shows an embodiment modified from that of FIG. 1 in that the fuel cell stack 2 is surrounded by two flat heat-conducting elements 3, 9. In this embodiment, the two elements 3, 9 are arranged one above the other with respect to the outer surface 11 of the fuel cell stack 2. So you put a double jacket from each a flat heat-conducting element 3, 9, each with its associated Phase change material 4, 10 represents.

The phase change material 10 in this embodiment, for example, no nucleation associated, it initiates upon reaching its phase transition temperature independently the phase transition and thus releases the energy stored in it, or can record a further large energy input to initiate the phase transition upon reaching a correspondingly high temperature , and without further significant increase in temperature.

A simpler embodiment would also be conceivable in which no nucleation seed for the respective phase change materials is provided, or one in which only the phase change material 10 is provided with one

Crystallization seed is equipped, or in addition one in the two phase change materials 4 and 10 is assigned in each case a crystallization seed.

In Fig. 3, again by way of example, another

Embodiment of a fuel cell system 1 shown, in which a plurality of surface heat-conducting elements 3, 9, 12 and 13 are arranged on each outer side 11 of the fuel cell stack 2 in order to cover this as completely as possible and keep it as well as possible within the intended operating temperature range. That is, either as possible to protect against cooling below freezing for possibly accumulated therein water, or, when cooling, as soon as possible to raise again above this temperature point.

A second essential function may also be to prevent an exceeding of the fuel cell stack temperature by storing this energy in the phase change material in an upper operating temperature range of the fuel cell stack by subtracting further energy. As a result, in particular, a strong heat development of the full-load operation resulting from the Fuel cell system can be advantageously removed from the fuel cell stack and cached.

The output of this stored energy can by targeted initiation of a phase change on the control unit 7, for example, in partial load operation, back to the

Fuel cell system done. In particular, it is thereby possible to counteract an undershooting of an ideal operating temperature of the fuel cell stack in an additionally advantageous manner, so that this further improves the efficiency of this fuel cell system.

Although exemplified in FIG. 3, equipped with phase change materials 4, 10, 14 and 15 area thermally conductive elements 3, 9, 12 and 13 are each equipped with a crystallization nucleus 6 for controlled influence on the respective phase change, for the sake of clarity, however only one crystallization seed 6 via a line 8 with the control unit 7 exemplified.

The illustration in FIG. 4 shows an embodiment in which two areal thermally conductive elements 4, 9 associated with them phase change materials 4, 10 finger-like interlocking on the respective outer side 11 of the fuel cell stack 2 are arranged. The fuel cell stack 2 can thus be described as meander-shaped in this sectional view between these areal thermally conductive elements 3, 9 described. Here too, an insulation layer 5 is again shown by way of example on a side of the heat-conducting elements facing away from the fuel cell stack 2 for additional heat insulation.

5, a further embodiment is shown, in which the sheet-like heat-conducting element 3 with another, a phase change material comprehensive Heat storage element 16 is thermally conductively connected. This further heat storage element can, for. Example, be a heat exchanger, which is connected via lines 23 of a cooling circuit 18 to the fuel cell stack 2. As shown here, a of a coolant pump 20 through the lines 23 of the cooling circuit 18 pumped coolant via a Kühlbzw. Heating coil 19 energy from the phase change material 17 for supply to the fuel cell stack remove or this for rapid removal of a large, excess amount of energy supply the fuel cell stack. Thus, an additional energy storage component 16 is proposed for the likewise exemplarily illustrated first energy storage component in the form of the areal thermally conductive element 3 with its associated phase change material whose functionality has already been described above.

For influencing phase transitions of the

Phase change materials here again by way of example a control unit 7 is shown, which are connected via lines 8 with respective crystallization nuclei 6. By connecting the control unit 7 to this additional heat storage element 16, the control unit is also able here, a phase change of the phase change material stored therein, for. B. during a part load operation, selectively return to the fuel cell stack.

As a result, on the one hand holding the operating temperature of the fuel cell stack in an optimal

Operating temperature range are supported and on the other hand, the deducted in a full load operation of the fuel cell stack, excess energy to release the

Caching be removed from this again.

The cooling circuit of the fuel cell stack 2 may further include, as exemplified herein, a cooler 21 and optionally a fan 22 and further, not shown here elements. The connection of the cooling circuit 18 to the fuel cell stack takes place here by way of example via the inlet 24 and the outlet 25. Von der Representation of further elements and signal or energy-transmitting connections, in particular between radiator, fan, coolant pump, additional heat storage element 16, fuel cell stack 2 and the control unit 7 was also omitted here for reasons of clarity.

Claims

claims

1. Fuel cell system, comprising a fuel cell stack and associated therewith, a phase change material tempering, characterized in that the tempering comprise at least one separate from the functional elements of the fuel cell stack, an outer surface of the fuel cell stack surface heat-conducting associated element.

2. Fuel cell system according to claim 1, characterized in that one and / or a plurality of heat-conducting elements surround the fuel cell stack.

3. Fuel cell system according to one of the preceding claims, characterized in that the areal thermally conductive element comprises a phase change material.

4. Fuel cell system according to one of the preceding claims, characterized in that the areal thermally conductive element is thermally conductively connected to a further, a phase change material comprehensive heat storage element.

5. Fuel cell system according to one of the preceding claims, characterized in that the further heat storage element is coupled to a coolant circuit of the fuel cell stack.

6. Fuel cell system according to one of the preceding claims, characterized in that the temperature range for a phase change of a phase change material in the range of about 0 ⁰ C or slightly above.

7. Fuel cell system according to one of the preceding claims, characterized in that the temperature range for a phase change of the phase change material is approximately in the range of the maximum permissible coolant inlet temperature in the fuel cell stack or something below.

8. Fuel cell system according to one of the preceding claims, characterized in that a control unit is provided for initiating a phase change of the phase change material.

9. Fuel cell system according to one of the preceding claims, characterized in that the control unit is adapted to initiate a phase change of the phase change material before and / or during a start phase of the fuel cell stack.

10. Fuel cell system according to one of the preceding claims, characterized in that the control unit is adapted to a phase change of

Phase change material during a partial load operation of the fuel cell stack to initiate.

11. Fuel cell system according to one of the preceding claims, characterized in that the areal thermally conductive element has an insulation on the side facing away from the fuel cell stack.