Anode recirculation blower with integrated sensor

Abstract

A side channel compressor (1) for a fuel cell system (31) for conveying and / or compressing a gaseous medium, in particular hydrogen, has a housing (3) and a drive device (6), the housing (3) having a housing upper part (7) and a housing lower part (8); a compressor chamber (30) running around a rotational axis (4) in the housing (3) and having at least one surrounding side channel (19, 21); the invention relates to a compressor having a housing (3), having a compressor wheel (2) in the housing (3), which compressor wheel is rotatably arranged about the axis of rotation (4) and is driven by the drive (6), according to the invention, the compressor wheel (2) has blades (5) arranged in the region of the compressor chamber (30) in the circumferential direction thereof and has a gas inlet opening (14) and a gas outlet opening (16) which are formed on the housing (3) and which are in fluid communication with one another via the compressor chamber (30), in particular at least one side channel (19, 21). According to the invention, at least one sensor (18) is located in the housing (3) of the side-channel compressor (1), a measured variable "wall shear stress" is determined by means of the sensor (18), in particular by means of a surface hot film method, and the sensor (18) is located in an interruption region (15) of the compressor chamber (30) of the side-channel compressor (1). The invention further relates to a fuel cell system (31), to a method for operating a side channel compressor (1) and / or a fuel cell system (31), and to a method for producing a connected measurement channel-cover assembly (33).

Description

Technical Field

[0001] The present invention relates to a side channel compressor for a fuel cell system for conveying and / or compressing a gaseous medium, in particular hydrogen, which is particularly intended for use in a vehicle with a fuel cell drive. Furthermore, the present invention relates to a fuel cell system, a method for operating a side channel compressor and / or a fuel cell system, and a method for producing a combined measuring channel-cover assembly. Background Art

[0002] In the automotive sector, gaseous fuels, in addition to liquid fuels, will play an increasingly important role in the future. In particular, in vehicles with fuel cell drives, the hydrogen flow must be controlled. Here, the gas flow is no longer controlled discontinuously, as with the injection of liquid fuels. Instead, gas is drawn from at least one high-pressure tank and directed via the inlet line of a medium-pressure pipe system to an injector unit. The injector unit directs the gas to the fuel cell via a connecting line of a low-pressure pipe system. After flowing through the fuel cell, the gas is directed back to the injector unit via a return line. A side channel compressor can be interposed to support the gas return from both a flow and efficiency perspective. Side channel compressors are also used to support flow establishment in the fuel cell drive, particularly during (cold) starts after a certain period of vehicle idling. These side channel compressors are typically driven by electric motors, which are supplied with voltage from the vehicle battery during operation. When the fuel cell system is shut down and at low ambient temperatures, so-called ice bridges can form between the movable parts of the side channel compressor, particularly the compressor wheel and the housing.

[0003] DE 10 2019 201 183 and DE 10 2019 219 992 each disclose a side channel compressor for a fuel cell system for conveying and / or compressing a gaseous medium, in particular hydrogen. The side channel compressor may comprise a housing with a compressor wheel located therein, which is rotatably arranged about an axis of rotation and driven at least indirectly by a drive. The compressor wheel has a conveying unit arranged in the region of the compressor chamber on its circumference and has a gas inlet opening and a gas outlet opening formed in the housing, the gas inlet opening and the gas outlet opening being fluidically connected to one another via the compressor chamber, in particular, via at least one side channel. Furthermore, each side channel compressor has a discharge opening and / or a valve and / or a purge valve, by means of which nitrogen and / or water that may be contained in the gaseous medium to be conveyed can be discharged.

[0004] The side channel compressors known from DE 10 2019 201 183 and DE 10 2019 219 992 have certain disadvantages.

[0005] In order to maintain a high hydrogen concentration in the gaseous medium, a gas mixture rich in nitrogen and / or rich in water must be blown away and replaced with fresh hydrogen. This removal (absteuerung), especially "cleaning", is carried out in a time cycle because the determination of the nitrogen content cannot be simply achieved in measurement technology (e.g., by a mass spectrometer). Therefore, a lot of valuable hydrogen is also lost during the blowing away and / or "cleaning". Therefore, more hydrogen, for example, from a high-pressure tank must be added to the anode loop so that a high hydrogen concentration can be maintained in the gaseous medium accordingly. Therefore, the side channel compressors known from DE 10 2019 201 183 and DE 10 2019 219 992 have the following disadvantages: in the case of frequent blowing away and / or "cleaning", the efficiency is reduced and the hydrogen from the tank is consumed more quickly. Summary of the Invention

[0006] According to the present invention, a side channel compressor for a fuel cell system is provided, having the features of the independent claims, for conveying and / or compressing a gaseous medium, in particular hydrogen. Furthermore, according to the present invention, a fuel cell system, a method for operating a side channel compressor and / or a fuel cell system, and a method for producing a combined measuring channel-cover assembly are proposed and provided.

[0007] According to claim 1, a side channel compressor is proposed, in which at least one sensor is located in the housing of the side channel compressor, wherein the measured variable wall shear stress is determined by means of the sensor, in particular by means of a surface hot film method, and wherein the sensor is located in the interruption region of the compressor chamber of the side channel compressor. The advantage is achieved in a simple manner that the wall shear stress of the gaseous medium can be detected, wherein the wall shear stress is correlated with the viscosity of the gaseous medium. The viscosity can vary depending on the composition of the gaseous medium.

[0008] Therefore, by arranging the sensor in the interruption region, it is possible to precisely measure the wall shear stress, thereby enabling precise deductions about the composition and properties of the gaseous medium. Furthermore, arranging the sensor, which measures using the surface hot film method, in the interruption region allows for a compact and flat design of the sensor, with the sensor being particularly flat in the direction of the axis of rotation. This allows for a compact design of the entire side channel compressor, keeping the required installation space in the vehicle extremely small.

[0009] The dependent claims relate to preferred further developments of the invention.

[0010] According to an advantageous embodiment of the side-channel compressor, the sensor is arranged in the region of the first and / or second end face between the compressor impeller and the housing. The respective end face extends radially between the compressor impeller and the housing relative to the axis of rotation. This provides the advantage that the sensor is configured in a relatively narrow gap of a maximum of 2.5 mm, in particular 1 mm, in the interruption region between the compressor impeller and the housing, such that the properties of the gaseous medium can be effectively determined in this region by measuring the shear stress. In this interruption region, a short-circuit path exists, along which the pressure difference between the gas outlet opening and the gas inlet opening is reduced. This pressure difference and the narrow gap form a shear flow that is driven by the rotation of the impeller. The sensor can therefore measure the wall shear stress at this location, in particular by means of the surface hot film method. The wall shear stress can be measured much more accurately with the help of the sensor in the region of the first and / or second end face than in other regions of the side channel compressor. This is because the greatest influence on viscosity can be achieved in the region of the first and / or second end face between the compressor wheel and the housing at very small gap sizes. This improves the accuracy of the wall shear stress measurement results. This allows for better predictions of the composition of the gaseous medium, thus improving the efficiency of downstream control processes. Furthermore, the sensor can be integrated cost-effectively into the side channel compressor.

[0011] According to a particularly advantageous embodiment of the side channel compressor, the sensor is arranged as close as possible or directly in the region of the axial gap between the compressor impeller and the housing. The axial gap has a maximum dimension of 2.5 mm, in particular 1 mm. This arrangement allows the advantage that the sensor can be arranged in the region between the compressor impeller and the housing, wherein the sensor is particularly mounted on the housing, in which region the compressor impeller has an area that is only minimally covered by the blades. The region of the compressor impeller blades has openings extending axially relative to the axis of rotation between the blades. These openings can create interfering influences and potentially distort the measurement of the wall shear stress, or at least lead to a low degree of inaccuracy in the measurement results, since fluid eddies can occur in this region. Due to the advantageous embodiment of the side channel compressor according to the present invention, the influence of fluid eddies can be reduced, thereby improving the accuracy of the measurement results.

[0012] According to an advantageous embodiment of the side channel compressor, the sensor is arranged on the shroud surface between the compressor wheel and the housing. In particular, the shroud surface is axially disposed between the compressor impeller and the housing relative to the axis of rotation. This allows the wall shear stress of the gaseous medium to be measured at a location between the compressor impeller and the housing where, on the one hand, there are no openings between the impeller blades, so that at least minimal fluid eddies occur at this location. Consequently, negative flow influences can be reduced when measuring the wall shear stress in this region, thereby improving the accuracy of the measurement results. Furthermore, in an exemplary embodiment, the compressor impeller includes a circumferential outer limiting ring on its outer diameter, which extends rotationally symmetrically around the compressor impeller relative to the axis of rotation. This limiting ring can be used to prevent leakage flows and / or fluid eddies from the compressor chamber that extend radially outward from the compressor impeller in the direction of the axis of rotation. Consequently, the wall shear stress can be measured using the sensor in the region where the highest relative motion occurs between the compressor impeller surface and the housing surface, particularly in the region of the shroud surface. This further improves measurement accuracy and provides the greatest influence on the viscosity of the gaseous medium. In this way, it is therefore possible to determine precise conclusions about the properties and composition of the gaseous medium.

[0013] According to a particularly advantageous further development, the side channel compressor is designed such that the sensor is arranged in a channel, particularly a measuring channel, in the housing, wherein the channel is closed by a cover that delimits the channel. The gaseous medium is guided through the channel, wherein the pressure difference Δp between the channel inlet and outlet and the small channel diameter create a laminar flow, particularly in the channel. This allows for a maximum effect on the viscosity. The sensor measures the wall shear stress, particularly using a surface thermal film, and calculates the anode gas viscosity from the known Δp and the known channel flow geometry. The channel can have a diameter of up to 2.5 mm, particularly 1 mm. Since only the gas composition changes at the operating point during normal operation, changes in the wall shear stress can be used to infer changes in the gas mixture. In this embodiment of the side channel compressor according to the present invention, the sensor is protected from fluid turbulence caused by the blades, thereby improving the accuracy of the wall shear stress measurement results. Furthermore, a compact design of the sensor and the entire side channel compressor is possible, minimizing the required installation space in the vehicle.

[0014] According to an advantageous further development of the side channel compressor, the sensor and the cover are designed as a combined measuring channel-cover assembly, which can be preassembled and / or introduced as an installation unit into the recess of the housing. In this way, the advantage is achieved that the measuring channel-cover assembly can be quickly installed as an integrated solution when assembling the side channel compressor, so that the assembly time and processing time of the side channel compressor can be reduced. As a result, the assembly and processing costs for each manufactured side channel compressor can be reduced. In addition, in the event of maintenance and repairs, for example due to a fault, such as due to channel contamination or blockage or sensor malfunction, the combined measuring channel-cover assembly can be completely disassembled in one working step and replaced by a new unit. As a result, the maintenance costs and repair costs can be reduced.

[0015] According to an advantageous embodiment, the side channel compressor, in addition to sensors for measuring wall shear stress, also includes a rotational speed sensor and / or at least one pressure sensor and / or a controller and / or a purge valve. This provides the advantage that the required wall shear stress value can be determined using the sensors, the rotational speed of the compressor impeller using the rotational speed sensor, and the pressure difference using the at least one pressure sensor. From these values, the viscosity of the gaseous medium and / or its composition, in particular the hydrogen and / or nitrogen and / or water content, can be determined. The raw data is evaluated using the control valve, and, for example, an algorithm stored in the controller enables the purge valve to be opened rationally, so-called purge, to discharge nitrogen as required, with minimal or at least almost no hydrogen loss. This allows the efficiency of the side channel compressor and the entire fuel cell system to be improved in a simple manner, as less hydrogen is lost.

[0016] To achieve this objective, a fuel cell system with a side channel compressor is also proposed. According to an advantageous embodiment of the fuel cell system, the fuel cell system includes a controller and / or a purge valve. This allows for a compact design and arrangement of the components in a simple manner, while also preventing the controller and / or purge valve components from cooling down during long downtimes and at low external temperatures, particularly below 0°C, since these components are integrated into the fuel cell system.

[0017] Furthermore, a method for operating a side channel compressor and / or fuel cell system is proposed. In this case, in a first step, the wall shear stress is measured with the aid of a sensor. In a second step, the rotational speed n of the compressor wheel of the side channel compressor is detected with the aid of a controller or with the aid of an optional rotational speed sensor. In a third step, the flow velocity of the gaseous medium is calculated with the aid of a controller based on the determined rotational speed n. In a fourth step, a known pressure difference Δp is introduced, or in particular, the pressure difference Δp between the gas inlet opening and the gas outlet opening is measured with the aid of at least one optional pressure sensor. In addition, for example, the flow geometry of the channel and / or interruption area is known as a basis for this. In a fifth step, the viscosity of the gaseous medium at a specific time point T1 is determined. In a sixth step, the measured data are introduced in order to calculate the change in the composition of the gaseous medium by performing a delta calculation at a plurality of measuring points Tn with the aid of a controller.

[0018] Furthermore, a method for operating a side channel compressor and / or a fuel cell system is proposed, comprising the additional steps of calculating the change in the composition of the gaseous medium by delta calculation of a plurality of measuring points Tn by means of a controller and actuating a purge valve.

[0019] Furthermore, a method for producing a combined measuring channel cover assembly is proposed. In this method, in a first step, the sensor is introduced into and connected to the base body using a form-fitting, material-locking, or force-locking method. In a second step, the cover is installed to cover and / or cover the sensor and form the channel. In a third step, the measuring channel cover assembly is installed in the side channel compressor, particularly in the interruption area.

[0020] The invention is not limited to the embodiments described herein and the aspects highlighted therein. Instead, numerous modifications within the scope of the person skilled in the art are possible within the scope of the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be described in detail below with reference to the accompanying drawings.

[0022] The accompanying drawings show:

[0023] Figure 1 : Schematic cross-sectional view of a side channel compressor according to the present invention,

[0024] Figure 2 : According to the side channel compressor of the first embodiment Figure 1 The section marked with AA,

[0025] Figure 3 : A side view showing the combined measuring channel-cover assembly of a side channel compressor according to a second embodiment Figure 2 The part marked with II,

[0026] Figure 4 : A perspective view of a side channel compressor according to a third embodiment,

[0027] Figure 5 : a simplified description of a flow chart illustrating the method to be protected,

[0028] Figure 6 : Schematic block diagram of the component sensor, controller, speed sensor, pressure sensor and purge valve. DETAILED DESCRIPTION

[0029] according to Figure 1 The schematic diagram of FIG. 1 shows a longitudinal section through a side channel compressor 1 proposed according to the invention, which is designed rotationally symmetrically with respect to the axis of rotation 4 .

[0030] Here Figure 1 , a side channel compressor 1 for a fuel cell system 31 for conveying and / or compressing a gaseous medium, in particular hydrogen, is shown. The side channel compressor 1 comprises a housing 3 and a drive 6. The housing 3 comprises an upper housing part 7 and a lower housing part 8. Furthermore, the housing 3 comprises a compressor chamber 30 extending circumferentially about an axis of rotation 4, with at least one circumferential side channel 19, 21. The housing 3 comprises a compressor wheel 2 located in the housing 3, rotatably arranged about the axis of rotation 4 and driven by the drive 6. The compressor wheel 2 comprises blades 5 arranged on its circumference in the region of the compressor chamber 30 and a gas inlet opening 14 and a gas outlet opening 16 formed in the housing 3. The gas inlet and gas outlet openings are in fluid communication with one another via the compressor chamber 30, in particular via the at least one side channel 19, 21. The side channel compressor 1 comprises at least one bearing 27, 47. The at least one side channel 19 , 21 can extend circumferentially around the rotation axis 4 at least in a subregion of the housing 3 , wherein an interruption region 15 is formed in the housing 3 in that subregion of the housing 3 in which the at least one side channel 19 , 21 is not formed.

[0031] In addition Figure 1 , the drive device 6 is designed as an axial field motor 6 having a stator 11 and a rotor part 17, wherein the stator 11 and the rotor part 17 are designed to be circular disk-shaped around the rotation axis 4, and wherein the stator 11 is arranged next to the rotor part 17 in the direction of the rotation axis 4. In this case, the rotor part 17 can be at least indirectly located on or in the hub disk 23 of the compressor impeller 2. In addition, Figure 1, the side channel compressor 1 has a stator chamber 42 and a rotor chamber 44, wherein at least some components of the drive device 6 are arranged in these chambers 42, 44. The housing upper part 7 has a continuous wall 29, which is located between the stator chamber 42 and the rotor chamber 44 and separates the two chambers from each other by fluid. The stator chamber 42 is also at least partially surrounded and / or enclosed by the stator housing 39. The housing lower part 8 has a cylindrical journal 12, wherein the journal 12 extends in the direction of the rotation axis 4 such that its circumference extends around the rotation axis 4, and wherein the first bearing 27 and / or the second bearing 47 contact the circumference of the journal 12 in a radial direction relative to the rotation axis 4. The drive device 6 can be embodied as an axial field motor 6 having a stator 11 and a rotor component 17, wherein the stator 11 is arranged adjacent to the rotor component 17 in the direction of the rotation axis 4. Furthermore, the side channel compressor 1 has a cylindrical journal 12, wherein the journal 12 extends in the direction of the rotation axis 4 such that its circumference extends circumferentially around the rotation axis 4. The first bearing 27 and / or the second bearing 47 are in contact with the circumference of the journal 12 in the radial direction relative to the rotation axis 4.

[0032] In addition Figure 1 As shown in FIG, the compressor impeller 2 has a hub disk 23 on its inner diameter. The compressor impeller 2 is connected to the hub 9 via the region of the hub disk 23. The hub 9 has an inner bore 20 within the inner bore 20. The embodiment of the side channel compressor 1 according to the invention provides that at least one sensor 18 is located in the housing 3 of the side channel compressor 1. The measured variable wall shear stress is determined using the sensor 18, in particular using a surface hot film method, and the sensor 18 is located in the interruption region 15 of the compressor chamber 30 of the side channel compressor 1. The sensor 18 can be located in the region of a first end face 24 and / or a second end face 26 between the compressor impeller 2 and the housing 3. The end faces 24, 26 extend radially between the compressor impeller 2 and the housing 3 relative to the axis of rotation 4. In an exemplary advantageous embodiment, the sensor 18 is located in a region of very small gap dimensions between the compressor impeller 2 and the housing 3. The sensor 18 is arranged as close as possible to or directly in the region of the corresponding first axial gap 28 between the compressor impeller 2 and the housing 3. The respective first axial gap 28 is located in the region of the inner diameter of the blade 5 facing the axis of rotation 4, whereas the respective second axial gap 32 is located in the region of the outer diameter of the blade 5 facing away from the axis of rotation 4. In another exemplary embodiment of the side channel compressor 1, the sensor 18 can be located in the region of a shroud surface 34 of the housing 3.

[0033] The present invention is based on the object of using a side channel compressor 1 to provide defined conditions for sensor 18, enabling simple measurement of the anode gas composition. The wall shear stress is used as a measured variable, which is dependent on the velocity and viscosity of the medium. The viscosity varies with the gas composition. Any water present in the gaseous medium is initially separated by high radial forces or conveyed away through gas outlet opening 16.

[0034] Figure 2 The side channel compressor 1 according to the first embodiment is shown in FIG. Figure 1 The section marked with AA in FIG. Here, the gaseous medium is supplied to the side channel compressor 1, in particular the compressor impeller 2 and / or the corresponding side channels 19, 21, via the gas inlet opening 14. The gaseous medium is compressed by the compressor impeller 2 rotating in the direction of rotation 41 and leaves the side channel compressor 1 at a higher pressure via the gas outlet opening 16. In the interruption area 15, there is a short-circuit path, on which the pressure difference between the outlet and the inlet is reduced. This pressure difference and the narrow gap form a shear flow, which is driven by the rotation of the compressor impeller 2. The sensor 18 measures the wall shear stress at this location via the surface thermal film and determines the viscosity of the gaseous medium from the known parameters of the pressure difference and the rotational speed of the compressor impeller 2. The sensor 18 can be placed in the area of the gap 35 in the housing 3. It is also shown that the sensor 18 can be located in the immediate vicinity of the first axial gap 28 and / or in the area of this axial gap.

[0035] exist Figure 3 The combined measuring channel and cover assembly 33 of the side channel compressor 1 according to the second embodiment is shown in a side view. Figure 2 Detailed view of the housing 3, designated II. Here, the sensor 18 is shown arranged in a base body 36 in a channel 25, in particular a measuring channel 25. The channel 25 is closed by a cover 22, with the cover 22 defining the channel 25. The sensor 18 and the cover 22 are designed as a combined measuring channel-cover assembly 33, which is preassembled and / or can be introduced as an installation unit 33 into a recess 35 of the housing 3. The gas flows through the channel 25 in the flow direction 10, passing by the sensor 18. Due to the geometry, in particular the diameter of the channel 25, the fluid 10 is present as a laminar flow 38.

[0036] Furthermore, in one embodiment according to the invention of the side channel compressor 1 , a method for producing the combined measuring channel cover assembly 33 is provided, comprising the following steps:

[0037] - providing a base body 36,

[0038] - the sensor 18 is introduced and connected to the base body 36 by means of a form-fitting, material-locking or force-fitting method,

[0039] - mounting the cover 22 to conceal the cover 22 and / or cover the sensor 18 and to form the channel 25,

[0040] The measuring channel cover assembly 33 is installed in the side channel compressor 1 , in particular in the interruption region 15 .

[0041] exist Figure 4 shows a perspective view of a side channel compressor 1 according to a third embodiment. Here, the sensor 18 is located in the region of a shroud surface 34 between the compressor wheel 2 and the housing 3, wherein the shroud surface 34 is formed on the housing 3, in particular in the housing lower part 8, axially relative to the rotational axis 4 between the compressor wheel 2 and the housing 3.

[0042] exist Figure 5 51 to 56 and the arrows therebetween illustrate in a highly simplified manner how a multi-stage method for operating a side channel compressor 1 may proceed. In a first method step 51, the wall shear stress is measured using sensor 18. In a second method step 52, the rotational speed n of the compressor wheel 2 of the side channel compressor 1 is measured using controller 43 or an optional rotational speed sensor 45. In a third method step 53, the flow velocity of the gaseous medium is calculated based on the determined rotational speed n, in particular using controller 43. In a fourth method step 54, a known and / or measured pressure difference Δp is used, or a measurement is performed using at least one optional pressure sensor 49 between gas inlet opening 14 and gas outlet opening 16, using known flow geometries such as those of channel 25 and / or interruption region 15. In a fifth method step 55, the viscosity of the gaseous medium at a specific time T is determined. In an optional sixth method step 56, a delta calculation is performed for a plurality of measurement points Tn using controller 43, and the purge valve 40 is actuated.

[0043] Figure 6The arrangement of the various components of the side channel compressor 1 and / or the fuel cell system 31 is shown. This arrangement is shown as a schematic block diagram of the components sensor 18, controller 43, optional rotational speed sensor 45, optional pressure sensor 49, and purge valve 40. The controller 43 and purge valve 40 do not necessarily need to be located in or on the side channel compressor 1; instead, they can be located in another area of the fuel cell system 31, particularly in the anode circuit. The side channel compressor 1 can be located in the anode circuit of the fuel cell system 31. The components, sensor 18 and / or rotational speed sensor 45 and / or optional pressure sensor 49, can provide measured values and data to the controller 43, which then controls the purge valve 40 based on a stored algorithm for evaluating the data. The purge valve 40 is only opened by actuation of the controller 43 if the gaseous phase has a high concentration of nitrogen and / or other components other than hydrogen.

Claims

1. A side channel compressor (1) for a fuel cell system (31) for conveying and / or compressing a gaseous medium, in particular hydrogen, comprising a housing (3) and a drive (6), wherein: The housing (3) comprises an upper housing part (7) and a lower housing part (8); a compressor chamber (30) extending in a circumferential manner around an axis of rotation (4) in the housing (3), the compressor chamber having at least one circumferential side channel (19, 21); a compressor impeller (2) located in the housing (3), the compressor impeller being rotatably arranged around the axis of rotation (4) and driven by the drive device (6), wherein the compressor impeller (2) has blades (5) arranged in the region of the compressor chamber (30) on its circumference and has a gas inlet opening (14) and a gas outlet opening (15) formed on the housing (3). An opening (16), the gas inlet opening and the gas outlet opening are fluidically connected to each other via the compressor chamber (30), in particular via at least one side channel (19, 21), wherein the compressor chamber (30) and the at least one side channel (19, 21) have an interruption region (15), characterized in that at least one sensor (18) is located in the housing (3) of the side channel compressor (1), wherein the measured variable "wall shear stress" is determined by means of the sensor (18), in particular by means of a surface hot film method, and wherein the sensor (18) is located in the interruption region (15) of the compressor chamber (30) of the side channel compressor (1).

2. The side channel compressor (1) according to claim 1, characterized in that The sensor (18) is arranged in the region of a first end face (24) and / or a second end face (26) between the compressor impeller (2) and the housing (3), wherein in particular the end faces (24, 26) are formed radially between the compressor impeller (2) and the housing (3) relative to the rotation axis (4).

3. The side channel compressor (1) according to claim 1 or 2, characterized in that The sensor (18) is arranged as close as possible or directly in the region of an axial gap (28) between the compressor wheel (2) and the housing (3).

4. The side channel compressor (1) according to claim 1, characterized in that The sensor (18) is arranged in the region of a shroud surface (34) between the compressor wheel (2) and the housing (3), wherein in particular the shroud surface (34) is formed on the housing (3) axially between the compressor wheel (2) and the housing (3) relative to the rotation axis (4).

5. A method side channel compressor (1) according to any one of the preceding claims, characterized in that The sensor (18) is arranged in the housing (3) in a channel (25), in particular a measuring channel (25), wherein the channel (25) is closed by means of a cover (22), wherein the cover (22) delimits the channel (25).

6. The side channel compressor (1) according to claim 5, characterized in that The sensor (18) and the cover (22) are designed as a combined measuring channel-cover assembly (33), which can be preassembled and / or introduced into a recess (35) of the housing (3) as a mounting unit (33).

7. Side channel compressor (1) according to any one of the preceding claims, characterized in that The side channel compressor (1) has, in addition to the sensor (18), a rotational speed sensor (45) and / or at least one pressure sensor (49) and / or a controller (43) thereof and / or a purge valve (40).

8. A fuel cell system (31) having a side channel compressor (1) according to any one of claims 1 to 7, wherein: The side channel compressor (1) is arranged in the anode circuit of the fuel cell system (31), and the fuel cell system (31) has the controller (43) and / or the purge valve (40).

9. A method for operating a side channel compressor (1) and / or a fuel cell system (31) according to any one of the preceding claims, comprising the following steps: - measuring the wall shear stress (51) by means of the sensor (18), - detecting (52) the rotational speed n of the compressor wheel (2) of the side channel compressor (1) by means of the control unit (43) or by means of the optional rotational speed sensor (45), - calculating (53) the flow velocity of the gaseous medium using the controller (43) as a function of the ascertained rotational speed n, - introducing (54) a known pressure difference Δp between the gas inlet opening (14) and the gas outlet opening (16) or measuring (54) the pressure difference Δp, in particular by means of at least one optional pressure sensor (49), and a known flow geometry, for example the flow geometry of the channel (25) and / or the interruption region (15), - Determine (55) the viscosity of the gaseous medium at a specific point in time T1.

10. The method for operating a side channel compressor (1) and / or a fuel cell system (31) according to claim 9, comprising the following additional steps: - calculating (56) the change in the composition of the gaseous medium by delta calculation of a plurality of measuring points Tn with the aid of the controller (43) and actuating the purge valve (40).

11. A method for producing a combined measuring channel-cover assembly according to claim 6, comprising the following steps: - providing a substrate (36), - introducing and connecting the sensor (18) into the base body (36) by means of a form-fitting, material-locking or force-fitting method, - installing the cover (22) to cover (22) and / or cover the sensor (18) and to construct the channel (25), - Installing the measuring channel-cover assembly (33) in the side channel compressor (1), in particular in the interruption area (15).

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