Cooling circuit for fuel cell

Abstract

A cooling circuit for a fuel cell includes at least one channel, a mechanical support, a first sensor, and a second sensor. Each channel is formed in a bipolar plate of the fuel cell, and is adapted to permit a cooling fluid to flow. The first sensor senses a flow rate of the cooling fluid. The second sensor senses an electrical conductivity of the cooling fluid. Both the first sensor and the second sensor are installed on the mechanical support.

Claims

1. A cooling circuit for a fuel cell, the cooling circuit comprising: at least one channel formed in a bipolar plate of the fuel cell, each channel being adapted to permit a cooling fluid to flow; a first sensor, which senses a flow rate of the cooling fluid; a second sensor, which senses an electrical conductivity of the cooling fluid; and a mechanical support on which the first and second sensors are installed, so as to form a double sensor thereon, wherein the first sensor, which senses the flow rate of the cooling fluid, includes two fins and a circuit for measuring a temperature difference between the two fins.

2. The cooling circuit according to claim 1, further comprising a sealing gasket positioned between the fins, electrodes corresponding to the second sensor, and a set of electronic components of the first and second sensors.

3. The cooling circuit according to claim 2, wherein the sealing gasket is made of silicone.

4. The cooling circuit according to claim 1, wherein the first and second sensors are adapted to make measurements of the flow rate and the electrical conductivity in real time.

5. The cooling circuit according to claim 1, further comprising a transmitter, which transmits measurements made by the first and second sensors to a controller of a fuel cell in which the cooling circuit is installed.

6. The cooling circuit according to claim 1, wherein the mechanical support is provided with a gasket, which is structured to prevent leakage of the cooling fluid to outside of the cooling circuit.

7. A cooling circuit for a fuel cell, the cooling circuit comprising: at least one channel formed in a bipolar plate of the fuel cell, each channel being adapted to permit a cooling fluid to flow; a first sensor, which senses a flow rate of the cooling fluid; a second sensor, which senses an electrical conductivity of the cooling fluid; and a mechanical support on which the first and second sensors are installed, so as to form a double sensor thereon, wherein the second sensor, which senses the electrical conductivity of the cooling fluid, includes two electrodes and a circuit for measuring an impedance between the two electrodes.

8. The cooling circuit according to claim 7, wherein the first and second sensors are adapted to make measurements of the flow rate and the electrical conductivity in real time.

9. The cooling circuit according to claim 7, further comprising a transmitter, which transmits measurements made by the first and second sensors to a controller of a fuel cell in which the cooling circuit is installed.

10. The cooling circuit according to claim 7, wherein the mechanical support is provided with a gasket, which is structured to prevent leakage of the cooling fluid to outside of the cooling circuit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other objects and advantages of the invention will become clearly apparent from the following description of a preferred, but non-limiting, embodiment, illustrated by the following figures, in which:

(2) FIG. 1 shows a mechanical support on which a flow rate sensor and a conductivity sensor are installed,

(3) FIG. 2 shows a functional block diagram of a sensor according to the invention and of a fuel cell controller, and

(4) FIG. 3 shows another embodiment of a mechanical support as shown in FIG. 1.

DESCRIPTION OF THE BEST EMBODIMENT OF THE INVENTION

(5) The present invention relates to a cooling circuit for a fuel cell. This cooling circuit comprises a double sensor 1, corresponding to a flow rate sensor and an electrical conductivity sensor, mounted on the same mechanical support 2. This mechanical support is installed on the terminal plate of the fuel cell through which the cooling circuit passes.

(6) The flow rate sensor is a sensor which is sensitive to the variations of thermal conductivity, and which comprises a support having, notably, a means for heating in controlled conditions, and a means for monitoring the temperature of this support. In stable conditions, this temperature is dependent both on the supply of heat from the heating means and on the dissipation of heat from the support into its ambient environment. The heat dissipation is itself dependent, on the one hand, on the difference between the temperature of the support and that of the ambient environment, and, on the other hand, on the thermal conductivity of the cooling liquid.

(7) Thus this double sensor 1 comprises a first pair of fins, each containing a platinum resistance (thermistor), immersed in the cooling liquid and identified by the reference 4, for making flow rate measurements. At the first fin, a voltage is applied to the resistance in order to heat it; the flow of cooling fluid cools this resistance, the degree of cooling of the resistance becoming greater as the flow rate increases. The second fin is used to measure the temperature of the cooling fluid. The applied voltage is regulated so as to maintain a constant temperature difference between the first resistance and the cooling fluid. The value of the applied voltage is measured and used to quantify the flow rate.

(8) However, it has been found that, in some situations, the application of a variable voltage may give rise to a problem of galvanic corrosion related to the potential. To avoid this, in a preferred embodiment, an alternating voltage with a mean value of zero is applied to the two resistances through a voltage divider bridge. The voltage difference between the two sides of the divider bridge is measured and used to quantify the flow rate.

(9) The double sensor 1 further comprises a second pair of larger fins, identified by the reference 3, for measuring the electrical conductivity. This measurement is made by measuring the impedance at each instant between the two fins forming electrodes. Since the two plates 4 have interchangeable functions, they are given the same reference in this case.

(10) In another embodiment, shown in FIG. 3, the two electrodes used for measuring the impedance are integrated into a single fin 3bis. This configuration does not modify the principle of the flow rate measurement, and it facilitates the integration of the system.

(11) For both the flow rate sensor and the electrical conductivity sensor, it is possible to interrupt the measurement in order to maximize the suppression of any potential that might cause corrosion.

(12) Calibration is required for both the flow rate sensor and the electrical conductivity sensor.

(13) Preferably, the double sensor should be mounted in such a way that the fins 3 and the fins 4 are orientated so as to offer minimum resistance to the movement of the cooling liquid; that is to say, the fins are positioned so as to be aligned in the direction of flow of the cooling liquid.

(14) In one embodiment, the mechanical support of the double sensor is provided with a gasket so as to prevent any leakage of cooling liquid to the exterior. There should also be a seal between the fins 3 and 4 and the set of electronic components, so as to prevent leaks of the cooling liquid. In the case of FIG. 1, this sealing barrier is made of silicone. The fins 3 and 4 are integrated into this silicone sealing barrier 5 with the sensitive parts of the fins left free so as to remain in contact with the cooling liquid.

(15) In some configurations, it is found that this silicone gasket fails to provide a perfect seal. Thus, in a preferred embodiment, the seal is provided by using a physical barrier printed directly on to the circuit, in which a gasket is installed.

(16) FIG. 2 shows a block diagram of the double sensor 1 mounted on a terminal plate 10 of a fuel cell. This figure shows two electrodes 40, corresponding to the electrodes integrated into the fins 3 or 3bis in FIG. 1, and two resistances 30 corresponding to the plates 4 in FIG. 1.

(17) The terminal plate 10 comprises the set of electronic components for shaping the signals output from the measuring devices 3 and 4. Thus the set 11 enables the impedance measurement made between the electrodes 40 to be shaped into a signal 11′. The set 12 enables the measurement of the voltage applied to the resistances 30 to be shaped into a signal 12′.

(18) After being conditioned in this way, the signals 11′ and 12′ are transmitted to a microcontroller 13 located in the cell controller. This microcontroller 13 then compares the signal 12′, corresponding to the flow rate measurement, with one or more predetermined values. Thus, in one example, if the value of the signal 12′ falls below a first predetermined value, the microcontroller triggers an alarm to inform a user of the reduction in flow rate. If the flow rate does not increase and the value of the signal 12′ falls below a second predetermined value, representing the minimum flow rate required to provide the proper cooling of the cell, this means that there is a risk of degradation of the cell, since cooling is no longer being carried out correctly. In an exemplary embodiment, the microcontroller then causes the fuel cell to be stopped. In a specific embodiment, the first predetermined value is about 10 liters per minute, and the second predetermined value is about 5 liters per minute.

(19) The microcontroller 13 also compares the signal 11′, corresponding to the electrical conductivity measurement, with one or more predetermined values. Thus, in one example, if the value of the signal 11′ rises above a third predetermined value, the microcontroller triggers an alarm to inform a user of the increase in electrical conductivity. If this conductivity does not decrease and the value of the signal 11′ rises above a fourth predetermined value, representing the maximum acceptable electrical conductivity for avoiding excessive corrosion of the fuel cell elements, then the microcontroller, in an exemplary embodiment, causes the fuel cell to be stopped. In a specific embodiment, the third value is about 12 microsiemens per centimeter, and the fourth value is about 16 microsiemens per centimeter.

(20) Thus the present invention makes it possible to propose a device for monitoring the cooling circuit of a fuel cell which can be used to detect any operating anomaly in the cooling circuit, and thus to stop the fuel cell in advance of any damage.