FR2914740A1 - Fluid e.g. gas, volumetric flow rate determining method for fuel cell of e.g. motor vehicle, involves measuring change of fluid temperature in points of pipe, obtaining profiles, and evaluating delay of one profile on another profile - Google Patents

Abstract

The method involves measuring change of temperature of a fluid in a point of a pipe by a temperature sensor (21), and obtaining an oscillating profile oscillating the temperature. The change of the fluid temperature is measured in another point of the pipe by a temperature sensor (22), and another oscillating profile oscillating the temperature is obtained. A delay (delta t) of the latter profile is evaluated on the former profile. A volumetric flow rate (Qv) of the fluid is determined in the pipe by a relation Qv equal to V>delta t, where V is volume of the pipe between the points. An independent claim is also included for a device for determining volumetric flow rate of a fluid circulated in a pipe.

Description

"Method for determining the volume flow rate of a fluid circulating in

  a pipe and associated device ".

  The invention mainly relates to a method for evaluating the volume flow rate of a fluid flowing in a pipe. The invention also relates to a device for implementing such a method.

  A fuel cell is an electrochemical device that converts chemical energy into electrical energy from a fuel, usually hydrogen, and an oxidant, oxygen, or an oxygen-containing gas such as air, the only product of the reaction being water accompanied by a release of heat and a production of electricity. Within the fuel cell, the overall chemical reaction resulting from the reactions occurring at the electrodes is as follows: H2 + 1- 02 - * H2O A fuel cell may be used to supply electrical power to any device such as For example, a computer, a mobile phone, but it can also be used to ensure the traction of a motor vehicle and / or the supply of electrical devices contained in a vehicle. A fuel cell consists of an assembly of elementary cells. An elementary cell 1 is diagrammatically shown in FIG. 1. Each elementary cell 1 comprises a protonic conductive electrolyte 2 which is sandwiched between two porous cathode 3 and anode electrodes 4 and which provides the electronic transfer between these two electrodes 3, 4. For this purpose, the electrolyte 2 may be a proton exchange polymer membrane 20 to 200 m thick, the resulting stack being a proton exchange membrane type cell or PEMFC cell. The assembly consisting of the electrolyte 2 and the two electrodes 3,4 forms a membrane electrode assembly (AME) 5 which is itself sandwiched between first 6 and second 7 bipolar plates made of an electrically conductive material. The two half-reactions leading to the synthesis reaction of the above-mentioned water are: At the anode: H2-2H + + 2e- At the cathode: O2 + 2H + + 2e-H2O. To ensure the operation of such a fuel cell, the cathode must be supplied with oxygen, generally from the air in automotive applications. For this, is provided an air inlet branch 8 and an air outlet 9. And the anode must be fed with hydrogen. For this purpose, there is provided a hydrogen intake branch 10 and a hydrogen outlet 11. Some fluid circuits passing through such an elementary cell require to be controlled in terms of flow. For example, with reference to FIG. 2, it is known to provide a recirculation loop 12 which makes it possible to ensure the circulation of the gases coming from the outlet 4a of the anode 4 via a circulator 13 and to mix it with the pure hydrogen circulating in the hydrogen intake branch 14 resulting from a supply of pure hydrogen 15 and feeding the inlet 4b of the anode 4. The circulator 13, which may be a pump or an ejector, is subjected to delicate operating conditions, and in particular, any presence of liquid water in the circulator 13 should be avoided. This is why a separator 16 makes it possible to collect and separate the water present in liquid form from the other species present in the gas coming from the outlet 4a of the anode 4, such as hydrogen, nitrogen and nitrogen. water vapor, the latter being introduced into the recirculation loop 12 described above. This operation of recirculation of the species resulting from the anodic reactions makes it possible on the one hand to mix all these species, and on the other hand to participate in the humidification of the feed gas of the anode circulating in the intake branch 14, these two functions contribute to the proper functioning of the fuel cell. To control the humidification of the feed gas, the operation of the circulator must be controlled. For this, it may be necessary to know the volume flow rate of the gas flowing in the recirculation loop 12. A measurement of this flow rate is possible thanks to a sensor placed on the recirculation loop 12. But the presence of such a sensor generates a pressure drop 20 which causes an oversizing at the level of the circulator 13 in order to compensate for this pressure drop, and therefore an electrical over-consumption and a decrease in the efficiency of the consequent system. There are non-intrusive volume flowmeters, that is to say not creating a pressure drop, but this type of flowmeter is not necessarily adapted to a hydrogen recirculation loop of a fuel cell. and result in additional cost and integration constraint. Another example of fluid circuits in contact with the elementary cell 1 and requiring a volume flow measurement is the cooling circuit which makes it possible to control the temperature of the cell. Indeed, the chemical reactions induced in cathodic 4 and anodic electrodes 3 are exothermic.

  The heat released by these reactions is captured by a cooling circuit 17 shown diagrammatically in FIG. 3. With reference to this figure, a cooling circuit 17 comprises a cooling module 18 and a pump 19 ensuring the circulation of the coolant, this circuit passing through the cell by means of channels schematized by a cell 20 forming part of the elementary cell 1 of the fuel cell.

  The heat transfer fluid may be water or any other coolant such as brine. The cooling of the cell to be controlled, the operation of the pump must be controlled.

  To do this, it is necessary to know the volume flow rate of the fluid flowing through the pump 19. A measurement of this flow rate is possible with a sensor placed on the cooling circuit 17 but the major disadvantage of this solution is, as in the case of the hydrogen recirculation loop, the creation of a pressure drop which leads to over-sizing at the pump to compensate for these losses, as well as an over-consumption of electricity and a drop in the efficiency of the system. And non-intrusive volume flow meters are, as explained above, not necessarily adapted and entail additional cost. It is therefore proposed in the context of the invention, a method for determining the volume flow rate of a fluid flowing in a pipe by avoiding the use of a volume flow meter. For this purpose, the method for determining the volume flow rate of a fluid that circulates in a pipe of the invention is essentially characterized in that it comprises at least the steps of: measuring the evolution of the fluid temperature in a first point of the pipe (12,17) and obtaining a first temperature oscillating profile (25), measuring the evolution of the fluid temperature at a second point of the pipe (12,17) and obtaining a a second temperature oscillating profile (28), evaluating the delay At of the second profile (28) on the first profile (25), and determining the volume flow rate of the fluid Qv in the pipe by the relation: V Qv û At where V is the volume of the pipe between the first and second points. According to a first variant, the fluid is a heat transfer fluid that circulates in a fuel cell cell cooling circuit 1. According to a second variant, the fluid is a gas that circulates in a hydrogen recirculation circuit of a fuel cell. The invention also relates to a device for implementing the method described above, which comprises first and second temperature sensors respectively disposed at first and second points of a pipe. According to the first variant, the first and second sensors are arranged on a fuel cell cooling circuit. According to the second variant, the first and second sensors are arranged on a hydrogen recirculation circuit of a fuel cell. The invention will be better understood, and other objects, features, details and advantages thereof will appear more clearly in the following explanatory description made with reference to the accompanying diagrammatic drawings given solely by way of illustrative example. two variants of the invention and in which: - Figure 1 is a schematic representation of a fuel cell cell of the prior art, - Figure 2 is a schematic representation of a hydrogen recirculation device of the prior art, Figure 3 is a schematic representation of a cooling circuit of a fuel cell of the prior art; FIG. 4 is a schematic representation of the device of the invention according to a first variant applied to the hydrogen recirculation circuit of FIG. 2; Figure 5 is a schematic representation of the device of the invention according to a second variant applied to the cooling circuit of Figure 3; FIG. 6A represents the flow profile of the cooling circuit pump or the recirculation loop, or the profile of the electric signal generated by the battery; FIG. 6B represents the profile of the temperature of the battery; FIG. 6C represents the profile of the temperature taken at a first point of the pipe; and FIG. 6D shows the profile of the temperature taken at a second point of the pipe. The elements common to the device of the prior art of FIG. 2 and to the device of the invention of FIG. 4 will bear the same references. It is the same elements common to the device of the prior art of Figure 3 and the device of the invention of Figure 5.

  With reference to FIG. 4 and in accordance with the first variant of the invention, the hydrogen recirculation circuit 12 comprises a first temperature sensor 21 situated at a first point of the circuit and a second temperature sensor 22 located at a second point. of the circuit. The measurement made by the first sensor 21 makes it possible to obtain the oscillating profile 25 of the temperature in the pipe at the first point shown in FIG. 6C. The oscillations of this profile are periodic, driven by the periodic oscillations 26 in phase of the temperature of the cell 1 shown in FIG. 6B, they themselves in phase with the periodic oscillations 27 of the flow rate of the pump forming the circulator 13 or the power electrical generated by the battery shown in Figure 6A. And the measurement made by the second sensor 22 makes it possible to obtain the oscillating profile 28 of the temperature at the second point represented in FIG. 6C. This oscillating profile is also periodic and has a phase shift or delay Δt with respect to the profile of the temperature of FIG. 6C taken at the first point. From this measurement of the phase shift Δt and the volume V of the pipes between the first and second measurement points of the temperature, it is then possible to determine the volume flow rate of the gas flowing in the recirculation loop 12 according to the following relationship: Qv ù At

  where Qv is the volumetric flow rate of the gas to be determined, where V is the volume of the pipes between the first and second measurement points of the temperature, and where Δt is the measured phase shift. 30 Referring to FIG. 5 and according to the second variant of the invention, the cooling circuit 17 comprises a first temperature sensor 23 located at a first point of the circuit and a second temperature sensor 24 located at a second point of the circuit. The measurement made by the first sensor 23 makes it possible to obtain the oscillating profile 25 of the temperature at the first point represented in FIG. 6C.

  The oscillations of this profile are periodic driven by the periodic oscillations 26 in phase of the temperature of the cell shown in FIG. 6B, they themselves in phase with the periodic oscillations 27 of the flow rate of the cooling pump 19 or the electrical power generated. by the stack shown in Figure 6A. And the measurement made by the second sensor 24 makes it possible to obtain the oscillating profile 28 of the temperature at the second point represented in FIG. 6C. This oscillating profile 28 is also periodic and has a phase shift or delay Δt with respect to the profile of the temperature 25 of FIG. 6C taken at the first point. From this measurement of the phase shift Δt and the volume V of the pipes of the cooling circuit 17 between the first and second measurement points of the temperature, it is then possible to determine the volume flow rate of the fluid flowing in the cooling circuit 17 according to the following relation: V Qv ù At

  where Qv is the volumetric flow rate of the fluid to be determined, where V is the volume of the pipes between the first and second measurement points of the temperature, and where At is the measured phase shift. or delay At can be estimated, the temperature profile taken respectively by the first 21,23 and the second 22,24 sensor must be oscillating.

  For this, the circuit or the fluid channel of which one wishes to know the volume flow must be in contact with a system inducing such oscillations. In the examples previously described, these are either the oscillations of the electric power delivered by the fuel cell through which the hydrogen or heat transfer fluid circulates, or the oscillations of the flow rate of the pump 19 of the cooling circuit 17 or the oscillations periodic flow of the pump forming a circulator 13 of the hydrogen recirculation circuit 12 which induces an oscillating temperature profile 26 in the cell 1 of the cell, and thus oscillating profiles of the temperature of the fluid taken at the first 21,23 and second 22,24 points of the considered pipeline. The method of the invention therefore makes it possible to evaluate the volume flow rate of a fluid circulating in a pipe by dispensing with a volume flow meter. In the case of a replacement of a non-intrusive volume flowmeter, this method avoids oversizing of the pump and therefore over-consumption. Moreover, the absence of a flow meter makes the system less expensive and facilitates the integration of the fuel cell, particularly in the case of an application in the automotive field. It may also be envisaged to double this evaluation of the volume flow by the presence of a flow meter, this redundancy thus making it possible to diagnose a possible failure of the measurement and thus to make the system more reliable.

Claims (6)

  1. A method for determining the volume flow rate of a fluid flowing in a pipe, said method comprising at least the steps of: measuring the evolution of the temperature of the fluid at a first point of the pipe (12, 17 ) and obtaining a first temperature oscillating profile (25), measuring the evolution of the fluid temperature at a second point of the pipe (12, 17) and obtaining a second temperature oscillating profile (28). ), evaluation of the delay At of the second profile (28) on the first profile (25), and determination of the volume flow rate of the fluid Qv in the channel by the relation: V Qv ù At 20 where V is the volume of the pipe between the first and second points.   2. Method according to claim 1, characterized in that the fluid is a heat transfer fluid which circulates in a cooling circuit (17) of fuel cell cell 1.   3. Method according to claim 1, characterized in that the fluid is a gas flowing in a hydrogen recirculation circuit (12) of a fuel cell cell 30.   4. Device for implementing the method according to any one of claims 1 to 3, characterized in that it comprises first (21,23) and second (22,24) temperature sensors arranged respectively in first and second points of a pipe (12,17).   5. Device according to claim 4 for carrying out the method according to claim 2, characterized in that the first (23) and second (24) sensors are arranged on a cooling circuit (17) of fuel cell (1).   6. Device according to claim 5 for carrying out the method according to claim 3, characterized in that the first (21) and second (22) sensors are arranged on a hydrogen recirculation circuit (12) of a cell. Fuel cell.